Etude de la transmission inhibitrice mixte GABA/glycine dans le cervelet et le thalamus

Dans le système nerveux central des vertébrés, la transmission synaptique inhibitrice rapide est médiée par le GABA et la glycine. Le transporteur vésiculaire des acides aminés inhibiteurs (VIAAT) est capable d'accumuler ces deux neurotransmetteurs dans les mêmes vésicules synaptiques, conduisant fréquemment à leur co-libération. Les travaux présentés ici sont basés principalement sur l'étude de la cellule unipolaire en brosse du vestibulocervelet (CUB). Cette cellule reçoit d'une part des synapses inhibitrices mixtes provenant des cellules de Golgi et d'autre part une unique synapse glutamatergique formée par une fibre moussue. Cette configuration en fait un modèle idéal pour étudier les interactions entre inhibition mixte et excitation. La caractérisation de l'inhibition mixte reçue par les CUBs nous a permis d'en distinguer deux populations, l'une d'entre elles ne recevant pas d'inhibition GABAergique. Cette absence de composante GABAergique est corrélée à la présence de récepteurs métabotropiques au glutamate du groupe II à la synapse excitatrice, établissant un lien inédit entre les phénotypes moléculaires et fonctionnels des synapses inhibitrices mixtes et des synapses glutamatergiques sur un même neurone. La mise au point d'un protocole d'immunohistochimie permettant la détection efficace des récepteurs inhibiteurs aux synapses nous a permis de confirmer et d'étendre ces observations à d'autres structures du système nerveux central. Nous montrons ainsi une grande variété d'organisation moléculaire des synapses inhibitrices dans les noyaux profonds cérébelleux ainsi que dans les noyaux intralaminaires du thalamus.PARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Differential GABAergic and glycinergic inputs of inhibitory interneurons and purkinje cells to principal cells of the cerebellar nuclei

The principal neurons of the cerebellar nuclei (CN), the sole output of the olivo-cerebellar system, receive a massive inhibitory input from Purkinje cells (PCs) of the cerebellar cortex. Morphological evidence suggests that CN principal cells are also contacted by inhibitory interneurons, but the properties of this connection are unknown. Using transgenic, tracing, and immunohistochemical approaches in mice, we show that CN interneurons form a large heterogeneous population with GABA/glycinergic phenotypes, distinct from GABAergic olive-projecting neurons. CN interneurons are found to contact principal output neurons, via glycine receptor (GlyR)-enriched synapses, virtually devoid of the main GABA receptor (GABAR) subunits α1 and γ2. Those clusters account for 5% of the total number of inhibitory receptor clusters on principal neurons. Brief optogenetic stimulations of CN interneurons, through selective expression of channelrhodopsin 2 after viral-mediated transfection of the flexed gene in GlyT2-Cre transgenic mice, evoked fast IPSCs in principal cells. GlyR activation accounted for 15% of interneuron IPSC amplitude, while the remaining current was mediated by activation of GABAR. Surprisingly, small GlyR clusters were also found at PC synapses onto principal CN neurons in addition to α1 and γ2 GABAR subunits. However, GlyR activation was found to account for <3% of the PC inhibitory synaptic currents evoked by electrical stimulation. This work establishes CN glycinergic neurons as a significant source of inhibition to CN principal cells, forming contacts molecularly distinct from, but functionally similar to, Purkinje cell synapses. Their impact on CN output, motor learning, and motor execution deserves further investigation

L’homme et son environnement. L’approche interdisciplinaire sur l’évolution des territoires insulaires de l’archipel du Kvarner (Croatie)

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Settlement of the Kvarner archipelago (northern Adriatic): archeology, anthropology and environment

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Coexistence of state, choice, and sensory integration coding in barrel cortex LII/III

International audienceDuring perceptually guided decisions, correlates of choice are found as upstream as in the primary sensory areas. However, how well these choice signals align with early sensory representations, a prerequisite for their interpretation as feedforward substrates of perception, remains an open question. We designed a two alternative forced choice task (2AFC) in which mice compared stimulation frequencies applied to two adjacent vibrissae. The optogenetic silencing of individual columns in the primary somatosensory cortex (wS1) resulted in predicted shifts of psychometric functions, demonstrating that perception depends on focal, early sensory representations. Functional imaging of layer II/III single neurons revealed sensory, choice and engagement coding. From trial to trial, these three varied substantially, but independently from one another. Thus, coding of sensory and non-sensory variables co-exist in orthogonal subspace of the population activity, suggesting that perceptual variability does not originate from wS1 but rather from state or choice fluctuations in downstream areas

Mixed Inhibitory Synaptic Balance Correlates with Glutamatergic Synaptic Phenotype in Cerebellar Unipolar Brush Cells

International audienceInhibitory synapses display a great diversity through varying combinations of presynaptic GABA and glycine release and postsynaptic expression of GABA and glycine receptor subtypes. We hypothesized that increased flexibility offered by this dual transmitter system might serve to tune the inhibitory phenotype to the properties of afferent excitatory synaptic inputs in individual cells. Vestibulocerebellar unipolar brush cells (UBC) receive a single glutamatergic synapse from a mossy fiber (MF), which makes them an ideal model to study excitatory-inhibitory interactions. We examined the functional phenotypes of mixed inhibitory synapses formed by Golgi interneurons onto UBCs in rat slices. We show that glycinergic IPSCs are present in all cells. An additional GABAergic component of large amplitude is only detected in a subpopulation of UBCs. This GABAergic phenotype is strictly anti-correlated with the expression of type II, but not type I, metabotropic glutamate receptors (mGluRs) at the MF synapse. Immunohistochemical stainings and agonist applications show that global UBC expression of glycine andGABA(A) receptors matches the pharmacological profile of IPSCs. Paired recordings of Golgi cells and UBCs confirm the postsynaptic origin of the inhibitory phenotype, including the slow kinetics of glycinergic components. These results strongly suggest the presence of a functional coregulation of excitatory and inhibitory phenotypes at the single-cell level. Wepropose that slow glycinergic IPSCs may provide an inhibitory tone, setting the gain of the MF to UBC relay, whereas large and fast GABAergic IPSCs may in addition control spike timing in mGluRII-negative UBCs

Edinger-Westphal peptidergic neurons enable maternal preparatory nesting

International audienceOptimizing reproductive fitness in mammalians requires behavioral adaptations during pregnancy. Maternal preparatory nesting is an essential behavior for the survival of the upcoming litter. Brain-wide immediate early gene mapping in mice evoked by nesting sequences revealed that phases of nest construction strongly activate peptidergic neurons of the Edinger-Westphal nucleus in pregnant mice. Genetic ablation, bidirectional neuromodulation, and in vitro and in vivo activity recordings demonstrated that these neurons are essential to modulate arousal before sleep to promote nesting specifically. We show that these neurons enable the behavioral effects of progesterone on preparatory nesting by modulating a broad network of downstream targets. Our study deciphers the role of midbrain CART+ neurons in behavioral adaptations during pregnancy vital for reproductive fitness

NMDA Receptors with Incomplete Mg2+ Block Enable Low-Frequency Transmission through the Cerebellar Cortex

International audienceThe cerebellar cortex coordinates movements and maintains balance by modifying motor commands as a function of sensory-motor context, which is encoded by mossy fiber (MF) activity. MFs exhibit a wide range of activity, from brief precisely timed high-frequency bursts, which encode discrete variables such as whisker stimulation, to low-frequency sustained rate-coded modulation, which encodes continuous variables such as head velocity. While high-frequency MF inputs have been shown to activate granule cells (GCs) effectively, much less is known about sustained low-frequency signaling through the GClayer, which is impeded by a hyperpolarized resting potential and strong GABAA-mediated tonic inhibition of GCs. Here we have exploited the intrinsic MF network of unipolar brush cells to activate GCs with sustained low-frequency asynchronous MF inputs in rat cerebellar slices. We find that low-frequency MF input modulates the intrinsic firing of Purkinje cells, and that this signal transmission through the GC layer requires synaptic activation of Mg2+-block-resistant NMDA receptors (NMDARs) that are likely to contain the GluN2C subunit. Slow NMDAR conductances sum temporally to contribute approximately half the MF-GC synaptic charge at hyperpolarized potentials. Simulations of synaptic integration in GCs show that the NMDAR and slow spillover-activated AMPA receptor (AMPAR) components depolarize GCs to a similar extent. Moreover, their combined depolarizing effect enables the fast quantal AMPAR component to trigger action potentials at low MF input frequencies. Our results suggest that the weakMg(2+) block of GluN2C-containing NMDA Rs enables transmission of low-frequency MF signals through the input layer of the cerebellar cortex

A deep learning algorithm for 3D cell detection in whole mouse brain image datasets.

Understanding the function of the nervous system necessitates mapping the spatial distributions of its constituent cells defined by function, anatomy or gene expression. Recently, developments in tissue preparation and microscopy allow cellular populations to be imaged throughout the entire rodent brain. However, mapping these neurons manually is prone to bias and is often impractically time consuming. Here we present an open-source algorithm for fully automated 3D detection of neuronal somata in mouse whole-brain microscopy images using standard desktop computer hardware. We demonstrate the applicability and power of our approach by mapping the brain-wide locations of large populations of cells labeled with cytoplasmic fluorescent proteins expressed via retrograde trans-synaptic viral infection