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Jonathan MAPELLI

Professore Associato
Dipartimento di Scienze Biomediche, Metaboliche e Neuroscienze sede ex-Sc. Biomediche

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2023 - Biologically Plausible Information Propagation in a CMOS Integrate-and-Fire Artificial Neuron Circuit with Memristive Synapses [Articolo su rivista]
Benatti, Lorenzo; Zanotti, Tommaso; Gandolfi, Daniela; Mapelli, Jonathan; Puglisi, Francesco Maria

Neuromorphic circuits based on spikes are currently envisioned as a viable option to achieve brain-like computation capabilities in specific electronic implementations while limiting power dissipation given their ability to mimic energy efficient bio-inspired mechanisms. While several network architectures have been developed to embed in hardware the bio-inspired learning rules found in the biological brain, such as the Spike Timing Dependent Plasticity, it is still unclear if hardware spiking neural network architectures can handle and transfer information akin to biological networks. In this work, we investigate the analogies between an artificial neuron combining memristor synapses and rate-based learning rule with biological neuron response in terms of information propagation from a theoretical perspective. Bio-inspired experiments have been reproduced by linking the biological probability of release with the artificial synapses conductance. Mutual information and surprise have been chosen as metrics to evidence how, for different values of synaptic weights, an artificial neuron allows to develop a reliable and biological resembling neural network in terms of information propagation and analysis

2023 - Full-scale scaffold model of the human hippocampus CA1 area [Articolo su rivista]
Gandolfi, Daniela; Mapelli, Jonathan; MG Solinas, Sergio; Triebkorn, Paul; D’Angelo, Egidio; Jirsa, Viktor; Migliore, Michele

2022 - A Hybrid CMOS-Memristor Spiking Neural Network Supporting Multiple Learning Rules [Articolo su rivista]
Florini, Davide; Gandolfi, Daniela; Mapelli, Jonathan; Benatti, Lorenzo; Pavan, Paolo; Puglisi, Francesco Maria

Artificial intelligence (AI) is changing the way computing is performed to cope with real-world, ill-defined tasks for which traditional algorithms fail. AI requires significant memory access, thus running into the von Neumann bottleneck when implemented in standard computing platforms. In this respect, low-latency energy-efficient in-memory computing can be achieved by exploiting emerging memristive devices, given their ability to emulate synaptic plasticity, which provides a path to design large-scale brain-inspired spiking neural networks (SNNs). Several plasticity rules have been described in the brain and their coexistence in the same network largely expands the computational capabilities of a given circuit. In this work, starting from the electrical characterization and modeling of the memristor device, we propose a neuro-synaptic architecture that co-integrates in a unique platform with a single type of synaptic device to implement two distinct learning rules, namely, the spike-timing-dependent plasticity (STDP) and the Bienenstock-Cooper-Munro (BCM). This architecture, by exploiting the aforementioned learning rules, successfully addressed two different tasks of unsupervised learning.

2022 - A realistic morpho-anatomical connection strategy for modelling full-scale point-neuron microcircuits [Articolo su rivista]
Gandolfi, Daniela; Mapelli, Jonathan; Solinas, Sergio; De Schepper, Robin; Geminiani, Alice; Casellato, Claudia; D'Angelo, Egidio; Migliore, Michele

The modeling of extended microcircuits is emerging as an effective tool to simulate the neurophysiological correlates of brain activity and to investigate brain dysfunctions. However, for specific networks, a realistic modeling approach based on the combination of available physiological, morphological and anatomical data is still an open issue. One of the main problems in the generation of realistic networks lies in the strategy adopted to build network connectivity. Here we propose a method to implement a neuronal network at single cell resolution by using the geometrical probability volumes associated with pre- and postsynaptic neurites. This allows us to build a network with plausible connectivity properties without the explicit use of computationally intensive touch detection algorithms using full 3D neuron reconstructions. The method has been benchmarked for the mouse hippocampus CA1 area, and the results show that this approach is able to generate full-scale brain networks at single cell resolution that are in good agreement with experimental findings. This geometric reconstruction of axonal and dendritic occupancy, by effectively reflecting morphological and anatomical constraints, could be integrated into structured simulators generating entire circuits of different brain areas facilitating the simulation of different brain regions with realistic models.

2022 - Changes of the biophysical properties of voltage-gated Na+ currents during maturation of the sodium-taste cells in rat fungiform papillae [Articolo su rivista]
Bigiani, Albertino; Tirindelli, Roberto; Bigiani, Lorenzo; Mapelli, Jonathan

Taste cells are sensory receptors that undergo continuous turnover while they detect food chemicals and communicate with afferent nerve fibers. The voltage-gated sodium current (INa ) is a key ion current for generating action potentials in fully differentiated and chemo-sensitive taste cells, which use electrical signaling to release neurotransmitters. Here we show that, during the maturation of rat taste cells involved in salt detection (sodium cells), the biophysical properties of INa , such as voltage dependence of activation and inactivation, change significantly. Our results help understand how taste cells gain electrical excitability during turnover, a property critical to operate as chemical detectors that relay sensory information to nerve fibers.

2022 - Editorial: Brain-inspired computing: Neuroscience drives the development of new electronics and artificial intelligence [Articolo su rivista]
Gandolfi, Daniela; Puglisi, Francesco Maria; Serb, Alexander; Giugliano, Michele; Mapelli, Jonathan

2022 - Emergence of associative learning in a neuromorphic inference network [Articolo su rivista]
Gandolfi, D.; Puglisi, F. M.; Boiani, G. M.; Pagnoni, G.; Friston, K. J.; D'Angelo, E.; Mapelli, J.

Objective. In the theoretical framework of predictive coding and active inference, the brain can be viewed as instantiating a rich generative model of the world that predicts incoming sensory data while continuously updating its parameters via minimization of prediction errors. While this theory has been successfully applied to cognitive processes-by modelling the activity of functional neural networks at a mesoscopic scale-the validity of the approach when modelling neurons as an ensemble of inferring agents, in a biologically plausible architecture, remained to be explored.Approach.We modelled a simplified cerebellar circuit with individual neurons acting as Bayesian agents to simulate the classical delayed eyeblink conditioning protocol. Neurons and synapses adjusted their activity to minimize their prediction error, which was used as the network cost function. This cerebellar network was then implemented in hardware by replicating digital neuronal elements via a low-power microcontroller.Main results. Persistent changes of synaptic strength-that mirrored neurophysiological observations-emerged via local (neurocentric) prediction error minimization, leading to the expression of associative learning. The same paradigm was effectively emulated in low-power hardware showing remarkably efficient performance compared to conventional neuromorphic architectures.Significance. These findings show that: (a) an ensemble of free energy minimizing neurons-organized in a biological plausible architecture-can recapitulate functional self-organization observed in nature, such as associative plasticity, and (b) a neuromorphic network of inference units can learn unsupervised tasks without embedding predefined learning rules in the circuit, thus providing a potential avenue to a novel form of brain-inspired artificial intelligence.

2022 - Long-Term Synaptic Plasticity Tunes the Gain of Information Channels through the Cerebellum Granular Layer [Articolo su rivista]
Mapelli, Jonathan; Boiani, Giulia Maria; D’Angelo, Egidio; Bigiani, Albertino; Gandolfi, Daniela

A central hypothesis on brain functioning is that long-term potentiation (LTP) and depression (LTD) regulate the signals transfer function by modifying the efficacy of synaptic transmission. In the cerebellum, granule cells have been shown to control the gain of signals transmitted through the mossy fiber pathway by exploiting synaptic inhibition in the glomeruli. However, the way LTP and LTD control signal transformation at the single-cell level in the space, time and frequency domains remains unclear. Here, the impact of LTP and LTD on incoming activity patterns was analyzed by combining patch-clamp recordings in acute cerebellar slices and mathematical modeling. LTP reduced the delay, increased the gain and broadened the frequency bandwidth of mossy fiber burst transmission, while LTD caused opposite changes. These properties, by exploiting NMDA subthreshold integration, emerged from microscopic changes in spike generation in individual granule cells such that LTP anticipated the emission of spikes and increased their number and precision, while LTD sorted the opposite effects. Thus, akin with the expansion recoding process theoretically attributed to the cerebellum granular layer, LTP and LTD could implement selective filtering lines channeling information toward the molecular and Purkinje cell layers for further processing.

2021 - Experimental determination of shift-less aberration bases for sensorless adaptive optics in nonlinear microscopy [Articolo su rivista]
Talone, B.; Pozzi, P.; Cavagnini, M.; Polli, D.; Pozzi, G.; Mapelli, J.

Adaptive optics can improve the performance of optical systems and devices by correcting phase aberrations. While in most applications wavefront sensing is employed to drive the adaptive optics correction, some microscopy methods may require sensorless optimization of the wavefront. In these cases, the correction is performed by describing the aberration as a linear combination of a base of influence functions, optimizing an image quality metric as a function of the coefficients. The influence functions base is generally chosen to either efficiently represent the adaptive device used or to describe generic wavefronts in an orthogonal fashion. A rarely discussed problem is that most correction bases have elements which introduce, together with a correction of the aberration, a shift of the imaging field of view in three dimensions. While simple methods to solve the problem are available for linear microscopy methods, nonlinear microscopy techniques such as multiphoton or second harmonic generation microscopy require non-trivial base determination. In this paper, we discuss the problem, and we present a method for calibrating a shift-less base on a spatial light modulator for two-photon microscopy.

2021 - Modeling Early Phases of COVID-19 Pandemic in Northern Italy and Its Implication for Outbreak Diffusion [Articolo su rivista]
Gandolfi, Daniela; Pagnoni, Giuseppe; Filippini, Tommaso; Goffi, Alessia; Vinceti, Marco; D'Angelo, Egidio; Mapelli, Jonathan

The COVID-19 pandemic has sparked an intense debate about the hidden factors underlying the dynamics of the outbreak. Several computational models have been proposed to inform effective social and healthcare strategies. Crucially, the predictive validity of these models often depends upon incorporating behavioral and social responses to infection. Among these tools, the analytic framework known as “dynamic causal modeling” (DCM) has been applied to the COVID-19 pandemic, shedding new light on the factors underlying the dynamics of the outbreak. We have applied DCM to data from northern Italian regions, the first areas in Europe to contend with the outbreak, and analyzed the predictive validity of the model and also its suitability in highlighting the hidden factors governing the pandemic diffusion. By taking into account data from the beginning of the pandemic, the model could faithfully predict the dynamics of outbreak diffusion varying from region to region. The DCM appears to be a reliable tool to investigate the mechanisms governing the spread of the SARS-CoV-2 to identify the containment and control strategies that could efficiently be used to counteract further waves of infection.

2021 - Modeling Neurotransmission: Computational Tools to Investigate Neurological Disorders [Articolo su rivista]
Gandolfi, Daniela; Boiani, Giulia Maria; Bigiani, Albertino; Mapelli, Jonathan

The investigation of synaptic functions remains one of the most fascinating challenges in the field of neuroscience and a large number of experimental methods have been tuned to dissect the mechanisms taking part in the neurotransmission process. Furthermore, the understanding of the insights of neurological disorders originating from alterations in neurotransmission often requires the development of (i) animal models of pathologies, (ii) invasive tools and (iii) targeted pharmacological approaches. In the last decades, additional tools to explore neurological diseases have been provided to the scientific community. A wide range of computational models in fact have been developed to explore the alterations of the mechanisms involved in neurotransmission following the emergence of neurological pathologies. Here, we review some of the advancements in the development of computational methods employed to investigate neuronal circuits with a particular focus on the application to the most diffuse neurological disorders.

2021 - Real Time Generation of Three Dimensional Patterns for Multiphoton Stimulation [Articolo su rivista]
Pozzi, P.; Mapelli, J.

The advent of optogenetics has revolutionized experimental research in the field of Neuroscience and the possibility to selectively stimulate neurons in 3D volumes has opened new routes in the understanding of brain dynamics and functions. The combination of multiphoton excitation and optogenetic methods allows to identify and excite specific neuronal targets by means of the generation of cloud of excitation points. The most widely employed approach to produce the points cloud is through a spatial light modulation (SLM) which works with a refresh rate of tens of Hz. However, the computational time requested to calculate 3D patterns ranges between a few seconds and a few minutes, strongly limiting the overall performance of the system. The maximum speed of SLM can in fact be employed either with high quality patterns embedded into pre-calculated sequences or with low quality patterns for real time update. Here, we propose the implementation of a recently developed compressed sensing Gerchberg-Saxton algorithm on a consumer graphical processor unit allowing the generation of high quality patterns at video rate. This, would in turn dramatically reduce dead times in the experimental sessions, and could enable applications previously impossible, such as the control of neuronal network activity driven by the feedback from single neurons functional signals detected through calcium or voltage imaging or the real time compensation of motion artifacts.

2021 - The effects of the general anesthetic sevoflurane on neurotransmission: an experimental and computational study [Articolo su rivista]
Mapelli, J.; Gandolfi, D.; Giuliani, E.; Casali, S.; Congi, L.; Barbieri, A.; D'Angelo, E.; Bigiani, A.

The brain functions can be reversibly modulated by the action of general anesthetics. Despite a wide number of pharmacological studies, an extensive analysis of the cellular determinants of anesthesia at the microcircuits level is still missing. Here, by combining patch-clamp recordings and mathematical modeling, we examined the impact of sevoflurane, a general anesthetic widely employed in the clinical practice, on neuronal communication. The cerebellar microcircuit was used as a benchmark to analyze the action mechanisms of sevoflurane while a biologically realistic mathematical model was employed to explore at fine grain the molecular targets of anesthetic analyzing its impact on neuronal activity. The sevoflurane altered neurotransmission by strongly increasing GABAergic inhibition while decreasing glutamatergic NMDA activity. These changes caused a notable reduction of spike discharge in cerebellar granule cells (GrCs) following repetitive activation by excitatory mossy fibers (mfs). Unexpectedly, sevoflurane altered GrCs intrinsic excitability promoting action potential generation. Computational modelling revealed that this effect was triggered by an acceleration of persistent sodium current kinetics and by an increase in voltage dependent potassium current conductance. The overall effect was a reduced variability of GrCs responses elicited by mfs supporting the idea that sevoflurane shapes neuronal communication without silencing neural circuits.

2020 - Cellular-resolution mapping uncovers spatial adaptive filtering at the rat cerebellum input stage [Articolo su rivista]
Casali, S.; Tognolina, M.; Gandolfi, D.; Mapelli, J.; D'Angelo, E.

Long-term synaptic plasticity is thought to provide the substrate for adaptive computation in brain circuits but very little is known about its spatiotemporal organization. Here, we combined multi-spot two-photon laser microscopy in rat cerebellar slices with realistic modeling to map the distribution of plasticity in multi-neuronal units of the cerebellar granular layer. The units, composed by ~300 neurons activated by ~50 mossy fiber glomeruli, showed long-term potentiation concentrated in the core and long-term depression in the periphery. This plasticity was effectively accounted for by an NMDA receptor and calcium-dependent induction rule and was regulated by the inhibitory Golgi cell loops. Long-term synaptic plasticity created effective spatial filters tuning the time-delay and gain of spike retransmission at the cerebellum input stage and provided a plausible basis for the spatiotemporal recoding of input spike patterns anticipated by the motor learning theory.

2020 - Inhibitory Plasticity: From Molecules to Computation and Beyond [Articolo su rivista]
Gandolfi, Daniela; Bigiani, Albertino; Porro, Carlo Adolfo; Mapelli, Jonathan

Synaptic plasticity is the cellular and molecular counterpart of learning and memory and, since its first discovery, the analysis of the mechanisms underlying long-term changes of synaptic strength has been almost exclusively focused on excitatory connections. Conversely, inhibition was considered as a fixed controller of circuit excitability. Only recently, inhibitory networks were shown to be finely regulated by a wide number of mechanisms residing in their synaptic connections. Here, we review recent findings on the forms of inhibitory plasticity (IP) that have been discovered and characterized in different brain areas. In particular, we focus our attention on the molecular pathways involved in the induction and expression mechanisms leading to changes in synaptic efficacy, and we discuss, from the computational perspective, how IP can contribute to the emergence of functional properties of brain circuits.

2020 - Scattering Compensation for Deep Brain Microscopy: The Long Road to Get Proper Images [Articolo su rivista]
Pozzi, Paolo; Gandolfi, Daniela; Porro, Carlo Adolfo; Bigiani, Albertino; Mapelli, Jonathan

Multiphoton microscopy is the most widespread method for preclinical brain imaging when sub-micrometer resolution is required. Nonetheless, even in the case of optimal experimental conditions, only a few hundred micrometers under the brain surface can be imaged by multiphoton microscopy. The main limitation preventing the acquisition of images from deep brain structures is the random light scattering which, until recently, was considered an unsurmountable obstacle. When in 2007 a breakthrough work by Vellekoop and Mosk [1] proved it is indeed possible to compensate for random scattering by using high resolution phase modulators, the neuro-photonics community started chasing the dream of a multiphoton microscopy capable of reaching arbitrary depths within the brain. Unfortunately, more than 10 years later, despite a massive improvement of technologies for scattering compensation in terms of speed, performances and reliability, clear images from deep layers of biological tissues are still lacking. In this work, we review recent technological and methodological advances in the field of multiphoton microscopy analyzing the big issue of scattering compensation. We will highlight the limits hampering image acquisition, and we will try to analyze the road scientists must tackle to target one of the most challenging issue in the field of biomedical imaging.

2018 - Use of a 3D floating sphere culture system to maintain the neural crest-related properties of human dental pulp stem cells [Articolo su rivista]
Pisciotta, Alessandra; Bertoni, Laura; Riccio, Massimo; Mapelli, Jonathan; Bigiani, Albertino; Noce, Marcella La; Orciani, Monia; de Pol, Anto; Carnevale, Gianluca

Human dental pulp is considered an interesting source of adult stem cells, due to the low-invasive isolation procedures, high content of stem cells and its peculiar embryological origin from neural crest. Based on our previous findings, a dental pulp stem cells sub-population, enriched for the expression of STRO-1, c-Kit, and CD34, showed a higher neural commitment. However, their biological properties were compromised when cells were cultured in adherent standard conditions. The aim of this study was to evaluate the ability of three dimensional floating spheres to preserve embryological and biological properties of this sub-population. In addition, the expression of the inwardly rectifying potassium channel Kir4.1, Fas and FasL was investigated in 3D-sphere derived hDPSCs. Our data showed that 3D sphere-derived hDPSCs maintained their fibroblast-like morphology, preserved stemness markers expression and proliferative capability. The expression of neural crest markers and Kir4.1 was observed in undifferentiated hDPSCs, furthermore this culture system also preserved hDPSCs differentiation potential. The expression of Fas and FasL was observed in undifferentiated hDPSCs derived from sphere culture and, noteworthy, FasL was maintained even after the neurogenic commitment was reached, with a significantly higher expression compared to osteogenic and myogenic commitments. These data demonstrate that 3D sphere culture provides a favorable micro-environment for neural crest-derived hDPSCs to preserve their biological properties.

2017 - Activation of the CREB/c-Fos pathway during long-term synaptic plasticity in the cerebellum granular layer [Articolo su rivista]
Gandolfi, Daniela; Cerri, Silvia; Mapelli, Jonathan; Polimeni, Mariarosa; Tritto, Simona; Fuzzati-Armentero, Marie-Therese; Bigiani, Albertino; Blandini, Fabio; Mapelli, Lisa; D’Angelo, Egidio

The induction of long-term potentiation and depression (LTP and LTD) is thought to trigger gene expression and protein synthesis, leading to consolidation of synaptic and neuronal changes. However, while LTP and LTD have been proposed to play important roles for sensori-motor learning in the cerebellum granular layer, their association with these mechanisms remained unclear. Here, we have investigated phosphorylation of the cAMP-responsive element binding protein (CREB) and activation of the immediate early gene c-Fos pathway following the induction of synaptic plasticity by thetaburst stimulation (TBS) in acute cerebellar slices. LTP and LTD were localized using voltage-sensitive dye imaging (VSDi). At two time points following TBS (15 min and 120 min), corresponding to the early and late phases of plasticity, slices were fixed and processed to evaluate CREB phosphorylation (P-CREB) and c-FOS protein levels, as well as Creb and c-Fos mRNA expression. High levels of P-CREB and Creb/c-Fos were detected before those of c-FOS, as expected if CREB phosphorylation triggered gene expression followed by protein synthesis. No differences between control slices and slices stimulated with TBS were observed in the presence of an N-methyl-Daspartate receptor (NMDAR) antagonist. Interestingly, activation of the CREB/c-Fos system showed a relevant degree of colocalization with long-term synaptic plasticity. These results show that NMDAR-dependent plasticity at the cerebellum input stage bears about transcriptional and post-transcriptional processes potentially contributing to cerebellar learning and memory consolidation.

2017 - Computational capacity of a cerebellum model [Abstract in Atti di Convegno]
De Gernier, Robin; Solinas, SERGIO MAURO GAVINO; Rössert, Christian; Mapelli, Jonathan; Haelterman, Marc; Massar, Serge

2016 - Heterosynaptic GABAergic plasticity bidirectionally driven by the activity of pre- and postsynaptic NMDA receptors [Articolo su rivista]
Mapelli, Jonathan; Gandolfi, Daniela; Vilella, Antonietta; Zoli, Michele; Bigiani, Albertino

Dynamic changes of the strength of inhibitory synapses play a crucial role in processing neural information and in balancing network activity. Here, we report that the efficacy of GABAergic connections between Golgi cells and granule cells in the cerebellum is persistently altered by the activity of glutamatergic synapses. This form of plasticity is heterosynaptic and is expressed as an increase (long-term potentiation, LTPGABA) or a decrease (long-term depression, LTDGABA) of neurotransmitter release. LTPGABA is induced by postsynaptic NMDA receptor activation, leading to calcium increase and retrograde diffusion of nitric oxide, whereas LTDGABA depends on presynaptic NMDA receptor opening. The sign of plasticity is determined by the activation state of target granule and Golgi cells during the induction processes. By controlling the timing of spikes emitted by granule cells, this form of bidirectional plasticity provides a dynamic control of the granular layer encoding capacity.

2015 - High-throughput spatial light modulation two-photon microscopy for fast functional imaging [Articolo su rivista]
Pozzi, Paolo; Gandolfi, Daniela; Tognolina, Marialuisa; Chirico, Giuseppe; Mapelli, Jonathan; D'Angelo, Egidio

The optical monitoring of multiple single neuron activities requires high-throughput parallel acquisition of signals at millisecond temporal resolution. To this aim, holographic two-photon microscopy (2PM) based on spatial light modulators (SLMs) has been developed in combination with standard laser scanning microscopes. This requires complex coordinate transformations for the generation of holographic patterns illuminating the points of interest. We present a simpler and fully digital setup (SLM-2PM) which collects three-dimensional two-photon images by only exploiting the SLM. This configuration leads to an accurate placement of laser beamlets over small focal volumes, eliminating mechanically moving parts and making the system stable over long acquisition times. Fluorescence signals are diffraction limited and are acquired through a pixelated detector, setting the actual limit to the acquisition rate. High-resolution structural images were acquired by raster-scanning the sample with a regular grid of excitation focal volumes. These images allowed the selection of the structures to be further investigated through an interactive operator-guided selection process. Functional signals were collected by illuminating all the preselected points with a single hologram. This process is exemplified for high-speed (up to 1 kHz) two-photon calcium imaging on acute cerebellar slices.

2015 - Long-Term Spatiotemporal Reconfiguration of Neuronal Activity Revealed by Voltage-Sensitive Dye Imaging in the Cerebellar Granular Layer [Articolo su rivista]
Gandolfi, Daniela; Mapelli, Jonathan; D'Angelo, Egidio

Understanding the spatiotemporal organization of long-term synaptic plasticity in neuronal networks demands techniques capable of monitoring changes in synaptic responsiveness over extended multineuronal structures. Among these techniques, voltage-sensitive dye imaging (VSD imaging) is of particular interest due to its good spatial resolution. However, improvements of the technique are needed in order to overcome limits imposed by its low signal-to-noise ratio. Here, we show that VSD imaging can detect long-term potentiation (LTP) and long-term depression (LTD) in acute cerebellar slices. Combined VSD imaging and patch-clamp recordings revealed that the most excited regions were predominantly associated with granule cells (GrCs) generating EPSP-spike complexes, while poorly responding regions were associated with GrCs generating EPSPs only. The correspondence with cellular changes occurring during LTP and LTD was highlighted by a vector representation obtained by combining amplitude with time-to-peak of VSD signals. This showed that LTP occurred in the most excited regions lying in the core of activated areas and increased the number of EPSP-spike complexes, while LTD occurred in the less excited regions lying in the surround. VSD imaging appears to be an efficient tool for investigating how synaptic plasticity contributes to the reorganization of multineuronal activity in neuronal circuits.

2015 - The effect of desflurane on neuronal communication at a central synapse [Articolo su rivista]
Mapelli, Jonathan; Gandolfi, Daniela; Giuliani, Enrico; Prencipe, FRANCESCO PIO; Pellati, Federica; Barbieri, Alberto; D'Angelo, Egidio; Bigiani, Albertino

Although general anesthetics are thought to modify critical neuronal functions, their impact on neuronal communication has been poorly examined. We have investigated the effect induced by desflurane, a clinically used general anesthetic, on information transfer at the synapse between mossy fibers and granule cells of cerebellum, where this analysis can be carried out extensively. Mutual information values were assessed by measuring the variability of postsynaptic output in relationship to the variability of a given set of presynaptic inputs. Desflurane synchronized granule cell firing and reduced mutual information in response to physiologically relevant mossy fibers patterns. The decrease in spike variability was due to an increased postsynaptic membrane excitability, which made granule cells more prone to elicit action potentials, and to a strengthened synaptic inhibition, which markedly hampered membrane depolarization. These concomitant actions on granule cells firing indicate that desflurane re-shapes the transfer of information between neurons by providing a less informative neurotransmission rather than completely silencing neuronal activity.

2014 - The effect of anesthesia on neuronal communication [Poster]
Mapelli, Jonathan; Giuliani, Enrico; Gandolfi, D.; Congi, L.; Barbieri, Alberto; D'Angelo, E.; Bigiani, Albertino

One challenging aspect in the analysis of neuronal circuits is the lack of quantitative and objective measurements of network activity to be translated into functional states. For example, the clinical assessment of the consciousness state in a brain-injured, unresponsive patient can be hardly analyzed at the cellular and network level. General anesthesia employs different classes of molecules to modulate at various levels neuronal functional states. General anesthetics (GA) are known to progressively and selectively reduce consciousness, perception and motor control. In this work we have investigated in a simplified neuronal circuit the effect of GA on information transfer. The Shannon mutual information (MI) was used to evaluate how much the neuron response reflected the input stimuli versus its intrinsic variability, providing a statistical tool to dissect the contribution of spike timing to neural information transmission. The cerebellum granule cell (GrC), due to its limited number of excitatory inputs, can be used to calculate the Mutual Information (MI) and its variation during a perturbed state (e.g. under anesthesia). The MI was experimentally assessed by detecting action potentials elicited in response to specific inputs through whole-cell patch-clamp recordings in rat acute cerebellar slices (P18-24). In order to test the action of the application of GA, GABAergic currents elicited by inhibitory afferent connections were recorded. The action of GA (in particular Sevoflurane and Desflurane) increased (+120%) post-synaptic inhibitory currents (IPSCs) in less than 10 sec and was fully recovered in 30 sec. Furthermore, the action of GA was to markedly reduce the MI measured in control condition (-57.4%). This control condition was fully recovered after removal the anesthetics, therefore leaving unaltered neuronal activity. This approach will be applied to larger circuits and investigated with other techniques (e.g. Multielectrode array recordings or cellular imaging), moreover different concentration of anesthetics could lead to the identification of multiple functional states.

2014 - The spatiotemporal organization of cerebellar network activity resolved by two-photon imaging of multiple single neurons [Articolo su rivista]
Gandolfi, D; Pozzi, P; Tognolina, M; Chirico, G; Mapelli, Jonathan; D'Angelo, E.

In order to investigate the spatiotemporal organization of neuronal activity in local microcircuits, techniques allowing the simultaneous recording from multiple single neurons are required. To this end, we implemented an advanced spatial-light modulator two-photon microscope (SLM-2PM). A critical issue for cerebellar theory is the organization of granular layer activity in the cerebellum, which has been predicted by single-cell recordings and computational models. With SLM-2PM, calcium signals could be recorded from different network elements in acute cerebellar slices including granule cells (GrCs), Purkinje cells (PCs) and molecular layer interneurons. By combining WCRs with SLM-2PM, the spike/calcium relationship in GrCs and PCs could be extrapolated toward the detection of single spikes. The SLM-2PM technique made it possible to monitor activity of over tens to hundreds neurons simultaneously. GrC activity depended on the number of spikes in the input mossy fiber bursts. PC and molecular layer interneuron activity paralleled that in the underlying GrC population revealing the spread of activity through the cerebellar cortical network. Moreover, circuit activity was increased by the GABA-A receptor blocker, gabazine, and reduced by the AMPA and NMDA receptor blockers, NBQX and APV. The SLM-2PM analysis of spatiotemporal patterns lent experimental support to the time-window and center-surround organizing principles of the granular layer.

2013 - Gating of long-term potentiation by nicotinic acetylcholine receptors at the cerebellum input stage. [Articolo su rivista]
Prestori, F; Bonardi, C; Mapelli, L; Lombardo, P; Goselink, R; De Stefano, Me; Gandolfi, D; Mapelli, Jonathan; Bertrand, D; Schonewille, M; De Zeeuw, C; D'Angelo, E.

The brain needs mechanisms able to correlate plastic changes with local circuit activity and internal functional states. At the cerebellum input stage, uncontrolled induction of long-term potentiation or depression (LTP or LTD) between mossy fibres and granule cells can saturate synaptic capacity and impair cerebellar functioning, which suggests that neuromodulators are required to gate plasticity processes. Cholinergic systems innervating the cerebellum are thought to enhance procedural learning and memory. Here we show that a specific subtype of acetylcholine receptors, the α7-nAChRs, are distributed both in cerebellar mossy fibre terminals and granule cell dendrites and contribute substantially to synaptic regulation. Selective α7-nAChR activation enhances the postsynaptic calcium increase, allowing weak mossy fibre bursts, which would otherwise cause LTD, to generate robust LTP. The local microperfusion of α7-nAChR agonists could also lead to in vivo switching of LTD to LTP following sensory stimulation of the whisker pad. In the cerebellar flocculus, α7-nAChR pharmacological activation impaired vestibulo-ocular-reflex adaptation, probably because LTP was saturated, preventing the fine adjustment of synaptic weights. These results show that gating mechanisms mediated by specific subtypes of nicotinic receptors are required to control the LTD/LTP balance at the mossy fibre-granule cell relay in order to regulate cerebellar plasticity and behavioural adaptation.

2013 - Realistic modeling of neurons and networks: towards brain simulation [Articolo su rivista]
D'Angelo, E; Solinas, S; Garrido, J; Casellato, C; Pedrocchi, A; Mapelli, Jonathan; Gandolfi, D; Prestori, F.

Realistic modeling is a new advanced methodology for investigating brain functions. Realistic modeling is based on a detailed biophysical description of neurons and synapses, which can be integrated into microcircuits. The latter can, in turn, be further integrated to form large-scale brain networks and eventually to reconstruct complex brain systems. Here we provide a review of the realistic simulation strategy and use the cerebellar network as an example. This network has been carefully investigated at molecular and cellular level and has been the object of intense theoretical investigation. The cerebellum is thought to lie at the core of the forward controller operations of the brain and to implement timing and sensory prediction functions. The cerebellum is well described and provides a challenging field in which one of the most advanced realistic microcircuit models has been generated. We illustrate how these models can be elaborated and embedded into robotic control systems to gain insight into how the cellular properties of cerebellar neurons emerge in integrated behaviors. Realistic network modeling opens up new perspectives for the investigation of brain pathologies and for the neurorobotic field.

2013 - The cerebellar Golgi cell and spatiotemporal organization of granular layer activity [Articolo su rivista]
D'Angelo, E; Solinas, S; Mapelli, Jonathan; Gandolfi, D; Mapelli, L; Prestori, F.

The cerebellar granular layer has been suggested to perform a complex spatiotemporal reconfiguration of incoming mossy fiber signals. Central to this role is the inhibitory action exerted by Golgi cells over granule cells: Golgi cells inhibit granule cells through both feedforward and feedback inhibitory loops and generate a broad lateral inhibition that extends beyond the afferent synaptic field. This characteristic connectivity has recently been investigated in great detail and been correlated with specific functional properties of these neurons. These include theta-frequency pacemaking, network entrainment into coherent oscillations and phase resetting. Important advances have also been made in terms of determining the membrane and synaptic properties of the neuron, and clarifying the mechanisms of activation by input bursts. Moreover, voltage sensitive dye imaging and multi-electrode array recordings, combined with mathematical simulations based on realistic computational models, have improved our understanding of the impact of Golgi cell activity on granular layer circuit computations. These investigations have highlighted the critical role of Golgi cells in: generating dense clusters of granule cell activity organized in center-surround structures, implementing combinatorial operations on multiple mossy fiber inputs, regulating transmission gain and cut-off frequency, controlling spike timing and burst transmission, and determining the sign, intensity and duration of long-term synaptic plasticity at the mossy fiber-granule cell relay. This review considers recent advances in the field, highlighting the functional implications of Golgi cells for granular layer network computation and indicating new challenges for cerebellar research.

2013 - Theta-frequency resonance at the cerebellum input stage improves spike timing on the millisecond time-scale [Articolo su rivista]
Gandolfi, D; Lombardo, P; Mapelli, Jonathan; Solinas, S; D'Angelo, E.

The neuronal circuits of the brain are thought to use resonance and oscillations to improve communication over specific frequency bands (Llinas, 1988; Buzsaki, 2006). However, the properties and mechanism of these phenomena in brain circuits remain largely unknown. Here we show that, at the cerebellum input stage, the granular layer (GRL) generates its maximum response at 5–7 Hz both in vivo following tactile sensory stimulation of the whisker pad and in acute slices following mossy fiber bundle stimulation. The spatial analysis of GRL activity performed using voltage-sensitive dye (VSD) imaging revealed 5–7 Hz resonance covering large GRL areas. In single granule cells, resonance appeared as a reorganization of output spike bursts on the millisecond time-scale, such that the first spike occurred earlier and with higher temporal precision and the probability of spike generation increased. Resonance was independent from circuit inhibition, as it persisted with little variation in the presence of the GABAA receptor blocker, gabazine. However, circuit inhibition reduced the resonance area more markedly at 7 Hz. Simulations with detailed computational models suggested that resonance depended on intrinsic granule cells ionic mechanisms: specifically, Kslow (M-like) and KA currents acted as resonators and the persistent Na current and NMDA current acted as amplifiers. This form of resonance may play an important role for enhancing coherent spike emission from the GRL when theta-frequency bursts are transmitted by the cerebral cortex and peripheral sensory structures during sensory-motor processing, cognition, and learning.

2012 - Immediate early genes expression in the cerebellar cortex correlates with LTP and LTD induction [Abstract in Rivista]
Gandolfii, D; Cerri, S; Mapelli, Jonathan; Titto, S; Mapelli, L; Polimeni, M; Armentero, Mt; Blandini, F; D'Angelo, E.

Congresso di fisiologia

2012 - The effects of volatile halogenated anesthetics on information flow at the cerebellum input stage [Abstract in Rivista]
Mapelli, Jonathan; Gandolfi, D.; Giuliani, Enrico; Barbieri, Alberto; D'Angelo, E.; Bigiani, Albertino

The cerebellum is of crucial importance for sensory-motor integration and is also involved in cognitive processing. Blended anesthesia employs different molecules whose mechanisms of action are not fully understood. Among these, sevoflurane and desflurane are currently used in clinic for maintenance of general anesthesia. In this work, we have tested how anesthetics affect the flow of excitatory information transmitted by cerebellum granule cells (GCs). It is in fact still unknown the way the neuronal network activity is modulated during anesthesia. Whole-cell patch clamp recordings from GCs were performed in current-clamp mode in rat cerebellar slices. The bath application of sevoflurane (8%), on one hand dramatically reduced the total number of synaptically evoked spikes (-79%±10; n=4), on the other hand, the first spike latency and the temporal precision were increased (+23%±5; +32%±5 respectively). Furthermore, the spike timing data were used to estimate how anesthetics can modulate information transmission through the measure of Mutual Information (MI). Preliminary results show that the effect of sevoflurane perfusion was to reduce up to the 80% (n=4, p<0.05) the MI measured in control condition. Interestingly, the control condition was fully recovered after the removal of the anesthetic. These evidences indicate that anesthetics perfusion can potentially affect the cerebellar network which is fundamental for sensory-motor integration, memory formation and consolidation.

2012 - Theta-frequencyresonance emerges from intrinsic properties of neurons and synapses in the cerebellum granula layer circuit [Abstract in Rivista]
Gandolfi, D; Lombardo, P; Mapelli, Jonathan; Solinas, S; D'Angelo, E.

Congresso Nazionale

2011 - Immediate early genes regulation in rat cerebellar cortex during long-term synaptic plasticity induction [Abstract in Rivista]
Polimeni, M.; Gandolfi, D.; Cerri, S.; Mapelli, Jonathan; Tritto, S.; Alloni, M.; Armentero, M. T.; Blandini, F.; D’Angelo, E.

The cerebellum is one of the brain areas involved in learning and memory formation. Long-term synaptic plasticity is thought to play a pivotal role in supporting these functions. Moreover immediate Early Genes (IEGs) expression and de novo proteinsynthesis and/or modifi cation have been strictly associated with maintenance of Long-Term Potentiation (LTP) as well as memory consolidation and storage. Two highly conserved signalling cascades, PKA and MAPK, seem to be involved in earlytolate-LTP conversion; both pathway can activate CREB transcription factor through phosphorylation and P-CREB has been suggested to initiate the protein synthesisleading to late-LTP induction. The transcription factor c-fos is known to be rapidly and transiently induced in the Nervous System by a variety of stimuli and is thoughtto be directly involved in processes of neuronal plasticity including LTP. We used rat parasagittal cerebellar slices as a model system in which specific patterns of stimulation delivered to the mossy fi bers can induce both Long-Term Potentiationand Long-Term Depression (LTD), depending on local inhibition and other regulating factors. Using Voltage Sensitive Dye (VSD) imaging we obtained high-resolution maps of the spatial distribution of LTP/LTD induced from a Teta Burst Stimulus (TBS)application. Control and stimulated slices were fi xed at diff erent times from the TBS application and processed for in situ hybridization or immunohystochemistry in orderto detect IEGs mRNA expression patterns and protein expression/modifications. The expression pattern of c-fos and CREB mRNAs and their protein distribution and/or phosphorylation were then correlated with LTP/LTD maps generated by VSD imaging. Preliminary data indicate a signifi cant increase of P-CREB in the granular layersuggesting that CREB phosphorylation is induced as early as 15 minutes post TBS application. In situ hybridization experiments indicate a good correlation between c-fos and CREB mRNAs up-regulation and LTP distribution at 120 minutes post TBS. At the protein level, the comparison of immunofl uorescence signals and VSD immaging data indicate a clear correlation between c-Fos and P-CREB distribution and synaptic plasticity patterns.We are planning further experiments to confi rm these data and to test our experimental system in the presence of drugs that could interfere with the transcription, translation or post-translational protein regulation.

Gandolfi, D.; Mapelli, Jonathan; D'Angelo, E.

The sites and mechanisms of long-term synaptic plasticity (LTP and LTD) in the cerebellar cortex are object of debate. What is apparently lacking is a determination of the plastic changes occurring when the whole circuit is engaged. In this way, LTP and LTD may occur at multiple sites as well as in the intrinsic excitable mechanisms of these same neurons. In particular, we have tested the impact of theta burst stimulation (TBS) delivered to the mossy fibers (Mapelli and D'Angelo, 2007).Voltage-Sensitive Dye (VSD) imaging on rat cerebellar slices showed various areas of plasticity following TBS, with a remarkable prevalence of LTD in the granular layer and of LTP in the Purkinje cell layer. At the same time, firing changes were monitored in Purkinje cells (PCs) and molecular layer interneurons (MLIs) using paired loose cell-attached (n=5) and whole-cell recordings (n=5). The PCs showed enhanced probability of response and enhanced time precision with reduced first spike delay. This could be due either to a secondary reduction of MLIs activity (which showed depression of response in the majority of cases) or to enhanced parallel fiber – Purkinje cells transmission, or both. While these mechanistic hypotheses are currently under investigation, these results already indicate that afferent patterns cause distributed plasticity in the network suggesting that chains of changes are the salient aspect to be considered in order to interpret the processes of cerebellar learning.

2011 - The cerebellar network: from structure to function and dynamics [Articolo su rivista]
D’Angelo, E.; Mazzarello, P.; Prestori, F.; Mapelli, Jonathan; Solinas, S.; Lombardo, P.; Cesana, E.; Gandolfi, D.; Congi, L.

Since the discoveries of Camillo Golgi and Ramón y Cajal, the precise cellular organization of the cerebellum has inspired major computational theories, which have then influenced the scientific thought not only on the cerebellar function but also on the brain as a whole. However, six major issues revealing a discrepancy between morphologically inspired hypothesis and function have emerged. (1) The cerebellar granular layer does not simply operate a simple combinatorial decorrelation of the inputs but performs more complex non-linear spatio-temporal transformations and is endowed with synaptic plasticity. (2) Transmission along the ascending axon and parallel fibers does not lead to beam formation but rather to vertical columns of activation. (3) The olivo-cerebellar loop could perform complex timing operations rather than error detection and teaching. (4) Purkinje cell firing dynamics are much more complex than for a linear integrator and include pacemaking, burst-pause discharges, and bistable states in response to mossy and climbing fiber synaptic inputs. (5) Long-term synaptic plasticity is far more complex than traditional parallel fiber LTD and involves also other cerebellar synapses. (6) Oscillation and resonance could set up coherent cycles of activity designing a functional geometry that goes far beyond pre-wired anatomical circuits. These observations clearly show that structure is not sufficient to explain function and that a precise knowledge on dynamics is critical to understand how the cerebellar circuit operates

2010 - Brain plasticity and functionality explored by non-linear opticalmicroscopy [Abstract in Atti di Convegno]
Sacconi, L.; Allegra, L.; Buffelli, M.; Cesare, P.; Dangelo, E.; Gandolfi, D.; Grasselli, G.; Lotti, J.; Mapelli, Jonathan; Strata, P.; Pavone, F. S.

In combination with fluorescent protein (XFP) expression techniques, two-photon microscopy has become anindispensable tool to image cortical plasticity in living mice. In parallel to its application in imaging, multi-photonabsorption has also been used as a tool for the dissection of single neurites with submicrometric precision withoutcausing any visible collateral damage to the surrounding neuronal structures. In this work, multi-photon nanosurgery isapplied to dissect single climbing fibers expressing GFP in the cerebellar cortex. The morphological consequences arethen characterized with time lapse 3-dimensional two-photon imaging over a period of minutes to days after theprocedure. Preliminary investigations show that the laser induced fiber dissection recalls a regenerative process in thefiber itself over a period of days. These results show the possibility of this innovative technique to investigateregenerative processes in adult brain.In parallel with imaging and manipulation technique, non-linear microscopy offers the opportunity to optically recordelectrical activity in intact neuronal networks. In this work, we combined the advantages of second-harmonic generation(SHG) with a random access (RA) excitation scheme to realize a new microscope (RASH) capable of optically recordingfast membrane potential events occurring in a wide-field of view. The RASH microscope, in combination with bulkloading of tissuewith FM4-64 dye, was used to simultaneously record electrical activity from clusters of Purkinje cells in acute cerebellarslices. Complex spikes, both synchronous and asynchronous, were optically recorded simultaneously across a givenpopulation of neurons. Spontaneous electrical activity was also monitored simultaneously in pairs of neurons, whereaction potentials were recorded without averaging across trials. These results show the strength of this technique indescribing the temporal dynamics of neuronal assemblies, opening promising perspectives in understanding thecomputations of neuronal networks.

2010 - cerebellar circuit activation through the mossy fiber-parallel fiber pathway using high-resolution VSD imaging in acute cerebellar slices [Abstract in Rivista]
Gandolfi, D.; Mapelli, Jonathan; D'Angelo, E.

It is not yet fully clear how mossy fiber inputs activate the granular layer retransmitting signals through the ascending axon and parallel fibers to Purkinje cells. We have characterized the spatio-temporal properties of cerebellar circuit activation in response to mossy fiber stimulation by using Voltage-Sensitive Dye (VSD) imaging in sagittal and coronal rat cerebellar slices (P20-P25). Fluorescent signals generated by Di4-ANNEPS were sampled at 1 KHz with a Micam-Ultima camera (SciMedia). The granular layer was activated in spots of about 30 micrometer diameter showing distinct intensities of response with delays of 2.1±0.15 ms (n=15). Then activation propagated into the molecular and Purkinje cell layers with an additional 3.6±1.1 ms delay (n=10). Simultaneous patch-clamp recordings from granule cells and Purkinje cells showed a direct correlation between intracellular depolarization and VSD signal. In sagittal slices, mossy fiber stimulation activated the overlaying area supporting vertical transmission, while in coronal slices activation also propagated laterally demonstrating spread of excitation along the parallel fibers. Transmission through the granular layer and to the molecular layer was more pronounced using high-frequency bursts rather than single isolated stimuli (+85.5%, n=8, from 0.1 Hz to 500 Hz), was markedly reduced by NMDA receptor blockers (e.g. -17.9%, n=4, at 200 Hz) and was enhanced by GABA-A receptor blockers (e.g. +36.9 %; n=4 at 200 Hz). VSD recordings reveal therefore (1) that the granular layer activates in spots depending on NMDA and GABA-A receptors, (2) that signals are transmitted toward the molecular layer depending on the frequency of the mossy fiber input and (3) that Purkinje cell excitation through the ascending granule cell axon coexist with that due to parallel fiber transmission. These observations provide the basis for a detailed investigation of spatio-temporal signal processing in the cerebellar circuit.

2010 - Combinatorial responses controlled by synaptic inhibition in the cerebellum granular layer [Articolo su rivista]
Mapelli, Jonathan; Gandolfi, D.; D'Angelo, E.

The granular layer of cerebellum has been long hypothesized to perform combinatorial operations on incoming signals. Although this assumption is at the basis of main computational theories of cerebellum, it has never been assessed experimentally. Here, by applying high-resolution voltage-sensitive dye imaging techniques, we show that simultaneous activation of two partially overlapping mossy fiber bundles (either with single pulses or high-frequency bursts) can cause combined excitation and combined inhibition, which are compatible with the concepts of coincidence detection and spatial pattern separation predicted by theory. Combined excitation appeared as an area in which the combination of two inputs is greater than the arithmetic sum of the individual inputs and was enhanced by gamma-aminobutyric acid type A (GABA(A)) receptor blockers. Combined inhibition was manifest as an area where two inputs combined resulted in a reduction to less than half of the activity evoked from either one of the two inputs alone and was prevented by GABA(A) receptor blockers. The combinatorial responses occupied small granular layer regions (approximately 30 microm diameter), with combined inhibition being interspersed among extended areas of combined excitation. Moreover, the combinatorial effects lasted for tens of milliseconds and combined inhibition occurred only after termination of the stimuli. These combinatorial operations, if engaged by natural input patterns in vivo, may be important to influence incoming impulses organizing spatiotemporal spike sequences to be relayed to Purkinje cells

2010 - High-Pass Filtering and Dynamic Gain Regulation Enhance Vertical Bursts Transmission along the Mossy Fiber Pathway of Cerebellum. [Articolo su rivista]
Mapelli, Jonathan; D., Gandolfi; E., D'Angelo

Signal elaboration in the cerebellum mossy fiber input pathway presents controversial aspects, especially concerning gain regulation and the spot-like (rather than beam-like) appearance of granular to molecular layer transmission. By using voltage-sensitive dye imaging in rat cerebellar slices (Mapelli et al., 2010), we found that mossy fiber bursts optimally excited the granular layer above approximately 50 Hz and the overlaying molecular layer above approximately 100 Hz, thus generating a cascade of high-pass filters. NMDA receptors enhanced transmission in the granular, while GABA-A receptors depressed transmission in both the granular and molecular layer. Burst transmission gain was controlled through a dynamic frequency-dependent involvement of these receptors. Moreover, while high-frequency transmission was enhanced along vertical lines connecting the granular to molecular layer, no high-frequency enhancement was observed along the parallel fiber axis in the molecular layer. This was probably due to the stronger effect of Purkinje cell GABA-A receptor-mediated inhibition occurring along the parallel fibers than along the granule cell axon ascending branch. The consequent amplification of burst responses along vertical transmission lines could explain the spot-like activation of Purkinje cells observed following punctuate stimulation in vivo.

2010 - The circuit properties of the cerebellar cortex revealed by Voltage-Sensitive Dye (VSD) imaging [Abstract in Rivista]
Mapelli, Jonathan; Gandolfi, D.; D'Angelo, E.

Although the cellular physiology of cerebellar neurons has made remarkable progress, the analysis of circuit functional properties is still incomplete. In order to asses theoretical predictions, we have performed VSD imaging measurements addressing three main issues. 1) VSD imaging was used to measure combinatorial responses in the cerebellum granular layer showing "combined excitation" and "combined inhibition". These depended on whether the response were enhanced or reduced, lasted for tens of ms and were regulated by synaptic inhibition. This is the first demonstration of the presence of combinatorial operations in the cerebellum. 2) VSD imaging was used to measure responses to bursts at different frequencies. Transmission through the mossy fiber–granular layer-molecular layer pathway was frequency-dependent generating a cascade of two high-pass filters regulated by NMDA and GABA-A receptors. 3) VSD imaging was used to investigate patterns transmission from the granular to molecular layer. High-frequency bursts were enhanced along vertical transmission lines but not along parallel fibers, suggesting that they could be specialized to convey low-frequency signals throughout the cerebellum. These results support the hypothesis that the mossy fiber input of the cerebellar cortex implements a complex spatio-temporal filter, in which local computations (and potentially long-term synaptic plasticity) can differentially redistribute activation among the neuronal elements.

2010 - The spatio-temporal filtering hypothesis of the cerebellar cortex: evidence from VSD imaging [Abstract in Rivista]
Mapelli, Jonathan; Gandolfi, D.; D'Angelo, E.

The functional mechanisms of the cerebellar cortex are still object of debate and it is not fully clear how mossy fiber inputs are transformed in the granular layer and retransmitted to the molecular layer and Purkinje cells. Here the spatio-temporal properties of granular-to-molecular layer transmission in response to mossy fiber bursts of different frequencies have been investigated using voltage-sensitive dye imaging. The granular layer was optimally excited above ~50 Hz and the molecular layer responded above ~100 Hz with a steep gain curve. The high-pass filtering properties depended on GABA and NMDA receptors: NMDA receptors determined mossy fiber – granular layer frequency-dependence, while GABA receptors determined granular to molecular layer frequency-dependence. Moreover, GABA receptors reduced granular layer gain through a dynamic mechanism (-103%) rather than tonic inhibition (+17%). These results indicate that the mossy fiber pathway favors bursts-burst transmission, which is dynamically controlled by the local circuitry in a frequency dependent manner.

D'Angelo, E.; Solinas, S.; Mapelli, Jonathan; Prestori, F.; Lombardo, P.; Cesana, E.; Gandolfi, D.; Congi, L.

Aim: The cerebellum is classically depicted as a well defined circuit, whose basic function can be understood by considering the anatomical organization and the sign of neuronal interactions. However, local connectivity and neuronal and synaptic properties suggest the emergence of complex spatio-temporal dynamics. Here, experimental measurements are combined with computational models to investigate network interactions.Methods: Patch-clamp whole-cell recordings from granule and Golgi cells have been used to develop detailed models of the neurons and synapses. MEA and voltage-sensitive dye recordings in acute cerebellar slices were used to investigate the spatio-temporal structure of responses. Finally, we have developed a large-scale computational model of the cerebellar granular layer network (NEURON) and evaluated its ability to reproduce the spatio-temporal patterns of activity recorded in vitro and in vivo.Results: The granular layer network showed a series of remarkable properties in response to mossy fiber stimulation, that could be faithfully reproduced by the model:Granule cells emitted spikes for a limited time period (< 5 ms) before inhibition through the Golgi cell loop interrupted the output (time-window).Granule cells optimally transmitted spikes when the input frequency was higher than 100 Hz (high-pass filtering).Sustained and diffused mossy fiber activity generated oscillations through the reverberant Golgi cell loops (oscillation and resonance).Activity was organized with maximum excitation in the core and inhibition in the periphery of activated areas (center-surround).Conclusions: These results suggest that the granular layer can perform complex transformations on incoming signals behaving as an adaptable spatio-temporal filter. LTP and LTD at the mossy fiber – granule cells relay, by regulating the release machinery and postsynaptic responsiveness, could contribute to organize time-window, oscillation, filtering, and center-surround properties.

2008 - Optical recording of electrical activity in intact neuronal networks with random access second-harmonic generation microscopy. [Articolo su rivista]
Sacconi, L.; Mapelli, Jonathan; Gandolfi, D.; Lotti, J.; O'Connor, R. P.; D'Angelo, E.; Pavone, F. S.

One of the main challenges in understanding the central nervous system is to measure the network dynamics of neuronal assemblies, while preserving the computational role of individual neurons. However, this is not possible with current techniques. In this work, we combined the advantages of second-harmonic generation (SHG) with a random access (RA) excitation scheme to realize a new microscope (RASH) capable of optically recording fast membrane potential events occurring in a wide-field of view. The RASH microscope, in combination with bulk loading of tissue with FM4-64 dye, was used to simultaneously record electrical activity from clusters of Purkinje cells in acute cerebellar slices. Complex spikes, both synchronous and asynchronous, were optically recorded simultaneously across a given population of neurons. Spontaneous electrical activity was also monitored simultaneously in pairs of neurons, where action potentials were recorded without averaging across trials. These results show the strength of this technique in describing the temporal dynamics of neuronal assemblies, opening promising perspectives in understanding the computations of neuronal networks

2007 - Computational reconstruction of pacemaking and intrinsic electroresponsiveness in cerebellar golgi cells [Articolo su rivista]
S., Solinas; L., Forti; E., Cesana; Mapelli, Jonathan; E., De Schutter; E., D'Angelo

The Golgi cells have been recently shown to beat regularly in vitro (Forti et al., 2006. J. Physiol. 574, 711-729). Four main currents were shown to be involved, namely a persistent sodium current (I(Na-p)), an h current (I(h)), an SK-type calcium-dependent potassium current (I(K-AHP)), and a slow M-like potassium current (I(K-slow)). These ionic currents could take part, together with others, also to different aspects of neuronal excitability like responses to depolarizing and hyperpolarizing current injection. However, the ionic mechanisms and their interactions remained largely hypothetical. In this work, we have investigated the mechanisms of Golgi cell excitability by developing a computational model. The model predicts that pacemaking is sustained by subthreshold oscillations tightly coupled to spikes. I(Na-p) and I(K-slow) emerged as the critical determinants of oscillations. I(h) also played a role by setting the oscillatory mechanism into the appropriate membrane potential range. I(K-AHP), though taking part to the oscillation, appeared primarily involved in regulating the ISI following spikes. The combination with other currents, in particular a resurgent sodium current (I(Na-r)) and an A-current (I(K-A)), allowed a precise regulation of response frequency and delay. These results provide a coherent reconstruction of the ionic mechanisms determining Golgi cell intrinsic electroresponsiveness and suggests important implications for cerebellar signal processing, which will be fully developed in a companion paper (Solinas et al., 2008. Front. Neurosci. 2:4).

2007 - Fast-reset of pacemaking and theta-frequency resonance patterns in cerebellar Golgi cells: simulations of their impact in vivo [Articolo su rivista]
S., Solinas; L., Forti; E., Cesana; Mapelli, Jonathan; E., De Schutter; E., D'Angelo

The Golgi cells are inhibitory interneurons of the cerebellar granular layer, which respond to afferent stimulation in vivo with a burst-pause sequence interrupting their irregular background low-frequency firing (Vos et al., 1999a. Eur. J. Neurosci. 11, 2621-2634). However, Golgi cells in vitro are regular pacemakers (Forti et al., 2006. J. Physiol. 574, 711-729), raising the question how their ionic mechanisms could impact on responses during physiological activity. Using patch-clamp recordings in cerebellar slices we show that the pacemaker cycle can be suddenly reset by spikes, making the cell highly sensitive to input variations. Moreover, the neuron resonates around the pacemaker frequency, making it specifically sensitive to patterned stimulation in the theta-frequency band. Computational analysis based on a model developed to reproduce Golgi cell pacemaking (Solinas et al., 2008Front. Neurosci., 2:2) predicted that phase-reset required spike-triggered activation of SK channels and that resonance was sustained by a slow voltage-dependent potassium current and amplified by a persistent sodium current. Adding balanced synaptic noise to mimic the irregular discharge observed in vivo, we found that pacemaking converts into spontaneous irregular discharge, that phase-reset plays an important role in generating the burst-pause pattern evoked by sensory stimulation, and that repetitive stimulation at theta-frequency enhances the time-precision of spike coding in the burst. These results suggest that Golgi cell intrinsic properties exert a profound impact on time-dependent signal processing in the cerebellar granular layer.

2007 - The spatial organization of long-term synaptic plasticity at the input stage of the cerebellum [Articolo su rivista]
Mapelli, Jonathan; E., D'Angelo

The spatial organization of long-term synaptic plasticity [long-term potentiation (LTP) and long-term depression (LTD)] is supposed to play a critical role for distributed signal processing in neuronal networks, but its nature remains undetermined in most central circuits. By using multielectrode array recordings, we have reconstructed activation maps of the granular layer in cerebellar slices. LTP and LTD induced by theta-burst stimulation appeared in patches organized in such a way that, on average, LTP was surrounded by LTD. The sign of long-term synaptic plasticity in a given granular layer region was directly correlated with excitation and inversely correlated with inhibition: the most active areas tended to generate LTP, whereas the least active areas tended to generate LTD. Plasticity was almost entirely prevented by application of the NMDA receptor blocker, APV. This suggests that synaptic inhibition, through a control of membrane depolarization, effectively regulates NMDA channel unblock, postsynaptic calcium entry, and the induction of bidirectional synaptic plasticity at the mossy fiber-granule cell relay (Gall et al., 2005). By this mechanism, LTP and LTD could regulate the geometry and contrast of network computations, preprocessing the mossy fiber input to be conveyed to Purkinje cells and molecular layer interneurons.

2006 - Ionic mechanisms of autorhythmic firing in cerebellar Golgi cells [Articolo su rivista]
L., Forti; E., Cesana; Mapelli, Jonathan; E., D’Angelo

Although Golgi cells (GoCs), the main type of inhibitory interneuron in the cerebellar granular layer (GL), are thought to play a central role in cerebellar network function, their excitable properties have remained unexplored. GoCs fire rhythmically in vivo and in slices, but it was unclear whether this activity originated from pacemaker ionic mechanisms. We explored this issue in acute cerebellar slices from 3-week-old rats by combining loose cell-attached (LCA) and whole-cell (WC) recordings. GoCs displayed spontaneous firing at 1-10 Hz (room temperature) and 2-20 Hz (35-37 degrees C), which persisted in the presence of blockers of fast synaptic receptors and mGluR and GABAB receptors, thus behaving, in our conditions, as pacemaker neurons. ZD 7288 (20 microM), a potent hyperpolarization-activated current (Ih) blocker, slowed down pacemaker frequency. The role of subthreshold Na+ currents (INa,sub) could not be tested directly, but we observed a robust TTX-sensitive, non-inactivating Na+ current in the subthreshold voltage range. When studying repolarizing currents, we found that retigabine (5 microM), an activator of KCNQ K+ channels generating neuronal M-type K+ (IM) currents, reduced GoC excitability in the threshold region. The KCNQ channel antagonist XE991 (5 microM) did not modify firing, suggesting that GoC IM has low XE991 sensitivity. Spike repolarization was followed by an after-hyperpolarization (AHP) supported by apamin-sensitive Ca2+-dependent K+ currents (I(apa)). Block of I(apa) decreased pacemaker precision without altering average frequency. We propose that feed-forward depolarization is sustained by Ih and INa,sub, and that delayed repolarizing feedback involves an IM-like current whose properties remain to be characterized. The multiple ionic mechanisms shown here to contribute to GoC pacemaking should provide the substrate for fine regulation of firing frequency and precision, thus influencing the cyclic inhibition exerted by GoCs onto the cerebellar GL

2006 - LTP regulates burst initiation and frequency at mossy fiber-granule cell synapses of rat cerebellum experimental observations and theoretical predictions [Articolo su rivista]
T., Nieus; E., Sola; Mapelli, Jonathan; E., Saftenku; P., Rossi; E., D’Angelo

Long-term potentiation (LTP) is a synaptic change supposed to provide the cellular basis for learning and memory in brain neuronal circuits. Although specific LTP expression mechanisms could be critical to determine the dynamics of repetitive neurotransmission, this important issue remained largely unexplored. In this paper, we have performed whole cell patch-clamp recordings of mossy fiber-granule cell LTP in acute rat cerebellar slices and studied its computational implications with a mathematical model. During LTP, stimulation with short impulse trains at 100 Hz revealed earlier initiation of granule cell spike bursts and a smaller nonsignificant spike frequency increase. In voltage-clamp recordings, short AMPA excitatory postsynaptic current (EPSC) trains showed short-term facilitation and depression and a sustained component probably generated by spillover. During LTP, facilitation disappeared, depression accelerated, and the sustained current increased. The N-methyl-d-aspartate (NMDA) current also increased. In agreement with a presynaptic expression caused by increased release probability, similar changes were observed by raising extracellular [Ca(2+)]. A mathematical model of mossy fiber-granule cell neurotransmission showed that increasing release probability efficiently modulated the first-spike delay. Glutamate spillover, by causing tonic NMDA and AMPA receptor activation, accelerated excitatory postsynaptic potential (EPSP) temporal summation and maintained a sustained spike discharge. The effect of increasing neurotransmitter release could not be replicated by increasing receptor conductance, which, like postsynaptic manipulations enhancing intrinsic excitability, proved very effective in raising granule cell output frequency. Independent regulation of spike burst initiation and frequency during LTP may provide mechanisms for temporal recoding and gain control of afferent signals at the input stage of cerebellar cortex.

2006 - The synapsin domain E accelerates the exo-endocytotic cycle of synaptic vesicles in cerebellar Purkinje cells [Articolo su rivista]
A., Fassio; D., Merlo; Mapelli, Jonathan; A., Menegon; A., Corradi; M., Mete; S., Zappettini; G., Bonanno; F., Valtorta; E., D’Angelo; F., Benfenati

Synapsins are synaptic-vesicle-associated phosphoproteins implicated in the regulation of neurotransmitter release and excitability of neuronal networks. Mutation of synapsin genes in mouse and human causes epilepsy. To understand the role of the highly conserved synapsin domain E in the dynamics of release from mammalian inhibitory neurons, we generated mice that selectively overexpress the most conserved part of this domain in cerebellar Purkinje cells. At Purkinje-cell-nuclear-neuron synapses, transgenic mice were more resistant to depression induced by short or prolonged high-frequency stimulations. The increased synaptic performance was accompanied by accelerated release kinetics and shorter synaptic delay. Despite a marked decrease in the total number of synaptic vesicles, vesicles at the active zone were preserved or slightly increased. The data indicate that synapsin domain E increases synaptic efficiency by accelerating both the kinetics of exocytosis and the rate of synaptic vesicle cycling and decreasing depression at the inhibitory Purkinje-cell-nuclear-neuron synapse. These effects may increase the sensitivity of postsynaptic neurons to inhibition and thereby contribute to the inhibitory control of network activity