1,721,010 research outputs found
The spatio-temporal filtering hypothesis of the cerebellar cortex: evidence from VSD imaging
No full textThe 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
LONG-TERM PLASTICITY CHAINS IN THE CEREBELLAR CORTEX
No full textThe 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
cerebellar circuit activation through the mossy fiber-parallel fiber pathway using high-resolution VSD imaging in acute cerebellar slices
No full textIt 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
The circuit properties of the cerebellar cortex revealed by Voltage-Sensitive Dye (VSD) imaging
No full textAlthough 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
Functional characterization of Type IV basal cells in rat fungiform taste buds
No full textTaste buds, the end organs of taste, consist of a diverse population of sensory cells that is constantly renewed. Cell differentiation begins with Type IV basal cells, which are ovoid elements located inside the taste bud near its base. These cells are postmitotic precursors that give rise to all other cell types, including glial-like cells (Type I cells) and chemoreceptors (Type II and Type III cells). Despite their critical role in cell turnover, Type IV basal cells are relatively unknown in terms of functional features. Here, we used Lucifer yellow labeling and patch-clamp technique to investigate their electrophysiological properties in the rat fungiform taste buds. All Type IV basal cells showed voltage-gated sodium currents (INa), albeit at a far lower density (17 pA/pF) than chemoreceptors (444 pA/pF), which fire action potentials during sensory transduction. Furthermore, they lacked calcium homeostasis modulator currents, which are required for neurotransmitter release by some chemoreceptor types. Amiloride-sensitive epithelial sodium channel (ENaC) was found to be only present in a subset of Type IV basal cells. Interestingly, Type IV basal cells shared some membrane features with glial-like cells, such as high cell capacitance and low INa density; however, input resistance was greater in Type IV basal cells than in glial-like cells. Thus, although Type IV basal cells may eventually differentiate into distinct cell lineages, our findings indicate that they are quite homogeneous in terms of the electrophysiological characteristics, with the exception of functional ENaCs, which appear to be only expressed in one subset
Ionic mechanisms of autorhythmic firing and intrinsic electroresponsiveness in rat cerebellar Golgi cells
No full textCellular-resolution mapping uncovers spatial adaptive filtering at the rat cerebellum input stage
No full textLong-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
Heterosynaptic GABAergic plasticity bidirectionally driven by the activity of pre- and postsynaptic NMDA receptors
No full textDynamic 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
Metodo di generazione di immagine di un campione fluorescente
No full textIl metodo di generazione di immagine di un campione fluorescente comprendente i passi di: scansionare con mezzi di scansione punti fluorescenti di detto campione ottenendo punti fluorescenti scansionati; generare immagini di detti punti fluorescenti scansionati su mezzi di visualizzazione, detto scansionare comprendendo: predefinire un campo di scansione di detto campione che comprende un insieme di punti fluorescenti scansionabili ; irraggiare in sequenza e con mezzi di irraggiamento almeno un primo sotto-insieme di punti di detto insieme di punti ed almeno un secondo sotto-insieme di detto insieme di punti che è supplementare a detto primo sotto-insieme rispetto a detto insieme di punti
The spatial organization of long-term synaptic plasticity at the input stage of the cerebellum
Full text linkThe 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
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