Long-Lasting Novelty-Induced Neuronal Reverberation during Slow-Wave Sleep in Multiple Forebrain Areas

The discovery of experience-dependent brain reactivation during both slow-wave (SW) and rapid eye-movement (REM) sleep led to the notion that the consolidation of recently acquired memory traces requires neural replay during sleep. To date, however, several observations continue to undermine this hypothesis. To address some of these objections, we investigated the effects of a transient novel experience on the long-term evolution of ongoing neuronal activity in the rat forebrain. We observed that spatiotemporal patterns of neuronal ensemble activity originally produced by the tactile exploration of novel objects recurred for up to 48 h in the cerebral cortex, hippocampus, putamen, and thalamus. This novelty-induced recurrence was characterized by low but significant correlations values. Nearly identical results were found for neuronal activity sampled when animals were moving between objects without touching them. In contrast, negligible recurrence was observed for neuronal patterns obtained when animals explored a familiar environment. While the reverberation of past patterns of neuronal activity was strongest during SW sleep, waking was correlated with a decrease of neuronal reverberation. REM sleep showed more variable results across animals. In contrast with data from hippocampal place cells, we found no evidence of time compression or expansion of neuronal reverberation in any of the sampled forebrain areas. Our results indicate that persistent experience-dependent neuronal reverberation is a general property of multiple forebrain structures. It does not consist of an exact replay of previous activity, but instead it defines a mild and consistent bias towards salient neural ensemble firing patterns. These results are compatible with a slow and progressive process of memory consolidation, reflecting novelty-related neuronal ensemble relationships that seem to be context- rather than stimulus-specific. Based on our current and previous results, we propose that the two major phases of sleep play distinct and complementary roles in memory consolidation: pretranscriptional recall during SW sleep and transcriptional storage during REM sleep

Novel Experience Induces Persistent Sleep-Dependent Plasticity in the Cortex but not in the Hippocampus

Episodic and spatial memories engage the hippocampus during acquisition but migrate to the cerebral cortex over time. We have recently proposed that the interplay between slow-wave (SWS) and rapid eye movement (REM) sleep propagates recent synaptic changes from the hippocampus to the cortex. To test this theory, we jointly assessed extracellular neuronal activity, local field potentials (LFP), and expression levels of plasticity-related immediate-early genes (IEG) arc and zif-268 in rats exposed to novel spatio-tactile experience. Post-experience firing rate increases were strongest in SWS and lasted much longer in the cortex (hours) than in the hippocampus (minutes). During REM sleep, firing rates showed strong temporal dependence across brain areas: cortical activation during experience predicted hippocampal activity in the first post-experience hour, while hippocampal activation during experience predicted cortical activity in the third post-experience hour. Four hours after experience, IEG expression was specifically upregulated during REM sleep in the cortex, but not in the hippocampus. Arc gene expression in the cortex was proportional to LFP amplitude in the spindle-range (10–14 Hz) but not to firing rates, as expected from signals more related to dendritic input than to somatic output. The results indicate that hippocampo-cortical activation during waking is followed by multiple waves of cortical plasticity as full sleep cycles recur. The absence of equivalent changes in the hippocampus may explain its mnemonic disengagement over time

Role of the Lateral Paragigantocellular Nucleus in the Network of Paradoxical (REM) Sleep: An Electrophysiological and Anatomical Study in the Rat

The lateral paragigantocellular nucleus (LPGi) is located in the ventrolateral medulla and is known as a sympathoexcitatory area involved in the control of blood pressure. In recent experiments, we showed that the LPGi contains a large number of neurons activated during PS hypersomnia following a selective deprivation. Among these neurons, more than two-thirds are GABAergic and more than one fourth send efferent fibers to the wake-active locus coeruleus nucleus. To get more insight into the role of the LPGi in PS regulation, we combined an electrophysiological and anatomical approach in the rat, using extracellular recordings in the head-restrained model and injections of tracers followed by the immunohistochemical detection of Fos in control, PS-deprived and PS-recovery animals. With the head-restrained preparation, we showed that the LPGi contains neurons specifically active during PS (PS-On neurons), neurons inactive during PS (PS-Off neurons) and neurons indifferent to the sleep-waking cycle. After injection of CTb in the facial nucleus, the neurons of which are hyperpolarized during PS, the largest population of Fos/CTb neurons visualized in the medulla in the PS-recovery condition was observed in the LPGi. After injection of CTb in the LPGi itself and PS-recovery, the nucleus containing the highest number of Fos/CTb neurons, moreover bilaterally, was the sublaterodorsal nucleus (SLD). The SLD is known as the pontine executive PS area and triggers PS through glutamatergic neurons. We propose that, during PS, the LPGi is strongly excited by the SLD and hyperpolarizes the motoneurons of the facial nucleus in addition to local and locus coeruleus PS-Off neurons, and by this means contributes to PS genesis

Neuromodulation de l'activité des neurones monoaminergiques au cours du cycle veille-sommeil : Approches électrophysiologique et pharmacologique chez le rat vigile.

The noradrenergic (NA) neurones of the Locus Coeruleus (LC) and serotonergic neurones (5HT) of the dorsal raphe nucleus (DRN) are critically involved in the control of waking and sleep states. During wakefulness, these neurones exhibit a spontaneous tonic regular firing, that progressively decreases during slow-wave sleep (SWS) and cease during paradoxical (REM) sleep (PS) (PS-off neurones). The decrease and cessation of activity of NA and 5HT neurones could be a necessary condition to enter sleep and PS. However, the mechanisms underlying the state-dependent modulation of activity of NA and 5HT neurones across the sleep-wake cycle remain unsolved.On the basis of anatomical and electrophysiological data, we have suggested that the decrease and cessation of activity of NA LC, and 5HT DRN neurones is caused by (1) a de-activation, following the ceasing of excitatory synaptic inputs (2) auto-inhibitory mechanisms (3) an inhibitory action of adenosine (4) GABAergic and/or glycinergic afferences.In order to test these different hypotheses, we have developed an electrophysiological and micropharmacological approach in a new experimental model of un-anaesthetised rat in a stereotaxic restraint. This pain-less and stress-less technique, has allowed us to couple extracellular unit recording of NA and 5HT neurones and micro-iontophoresis of agonists and antagonists of endogenous neurotransmitters Our findings support the hypothesis according to which, the tonic activity of NA neurones depends upon their intrinsic pacemaker properties. The activity of 5HT neurones, in contrast, would at least in part depend upon the tonic excitation from NA neurones. We have also determined that GABA and glycine exert a tonic inhibition of NA and 5HT neurones across the sleep-wake cycle. Our results further suggest that the glycinergic inhibitory tone is constant while the GABAergic tone progressively builds up during SWS and is maximal during PS. GABA would thus be the major neurotransmitter responsible for the inactivation of NA LC neurones and 5HT DRN neurones necessary for sleep onset and PS.Our anatomical results support the hypothesis that at least two distinct populations of GABAergic neurones are involved in the inactivation of NA and 5HT neurones during sleep. A first one, localized in the lateral and ventrolateral preoptic area would be active during SWS, and a second one, localized in the periaqueductal grey would be involved during PS.Les neurones noradrénergiques (NA) du locus coeruleus (LC) et sérotoninergiques (5-HT) du noyau du raphé dorsal (NRD) sont fortement impliqués dans la régulation des états d'éveil et de sommeils. Ces neurones ont, au cours de l'éveil, une activité spontanée tonique régulière qui diminue progressivement au cours du sommeil lent (SL) et cesse au cours du sommeil paradoxal (SP) (neurones "SP-OFF"). La diminution puis l'arrêt d'activité des neurones NA et 5-HT seraient une condition nécessaire à l'endormissement et à la survenue du SP. Les mécanismes à l'origine de cette modulation d'activité des neurones NA et 5-HT au cours du cycle veille-sommeil demeurent toutefois inexpliqués.Sur la base de données anatomiques et électrophysiologiques, il a été suggéré que la diminution puis la cessation d'activité des neurones NA du LC et 5-HT du NRD au cours du SL et du SP seraient dues (1) à une dé-activation consécutive à l'arrêt d'entrées synaptiques excitatrices, (2) à des mécanismes d'auto-inhibition, (3) à une action inhibitrice de l'adénosine, (4) à la mise en jeu d'afférences GABAergiques et/ou glycinergiques. Afin de tester ces différentes hypothèses nous avons développé une approche électrophysio-logique et micropharmacologique sur un nouveau modèle expérimental de rat non anesthésié en contention stéréotaxique. Cette technique, non stressante, nous a permis de réaliser l'enregistrement extracellulaire unitaire des neurones NA et 5-HT au cours du cycle veille-sommeil, couplé à la micro-iontophorèse d'agonistes et d'antagonistes des différents neurotransmetteurs.Les résultats obtenus soutiennent l'hypothèse selon laquelle l'activité tonique des neurones NA du LC au cours de l'éveil serait sous la dépendance de leurs propriétés intrinsèques. L'activité des neurones 5-HT du NRD, en revanche, dépendrait au moins en partie de l'influence excitatrice des neurones NA. Nous avons déterminé également que le GABA et la glycine exercent une influence inhibitrice tonique sur les neurones NA et 5-HT tout au long du cycle veille-sommeil. Nos résultats suggèrent en outre que le tonus inhibiteur glycinergique serait constant alors que le tonus GABAergique augmenterait progressivement au cours du SL et serait maximum au cours du SP. Le GABA serait ainsi le neurotransmetteur responsable de l'inactivation des neurones NA du LC et 5-HT du NRD nécessaire à l'endormissement et à la survenue au SP.Ces données soutiennent l'hypothèse selon laquelle deux populations de neurones GABAergiques seraient impliquées dans l'inactivation des neurones NA et 5-HT au cours du sommeil. L'une, localisée dans l'aire préoptique latérale et ventrolatérale serait mise en jeu au cours du SL, la seconde, localisée dans la substance grise péri-aqueducale, serait mise en jeu au cours du SP

INNOVATIVE ANIMAL-FREE TRAINING TO STEREOTAXIC NEUROSURGERY

International audienceStereotaxic neurosurgery in laboratory animals is a demanding technique used in a wide variety of studies in Neurosciences. Allowing to position one or more optical, electrical, or chemical probes, this approach remains indispensable for exploring brain functions. To date however, stereotaxic surgery is not taught as a subject per se, but rather passed-on behind closed door in research laboratories, resulting in a variety of practices and success rates. There is therefore a need to harmonize practices and enhance neuroscientists’ habilities to explore the brain in a valuable and reproducible way. Here we introduce an animal-free training on stereotaxic neurosurgery. The teacher/trainee ratio is 1:3 and, as a pre-requisite, trainees validate an online course on elementary concepts such as aseptic techniques, anesthesia and pain management, per-operative animal care, incisions and sutures (Vogt et al, 2011). The course covers the theoretical background of stereotaxy and focuses on techniques and surgical approaches to optimize spatial precision, while minimizing the risks of irreversible harm to the animal. Anatomy and functional organization of the brain are reminded, with a peculiar attention to the 3-dimensional arrangement of brain blood vessels and ventricles. Hands-on practice includes exercises to acquire an ease in the manipulation of a stereotaxic frame, micropositioners, rulers and verniers. Instead of real animals, trainees use realistic high-resolution simulation devices to measure stereotaxic coordinates of cranial landmarks and entry points, and safely prepare the skull for the insertion and fixation of a probe. Exercises are repeated as needed and the accurate placement of a probe can be checked promptly without the need of histology. Tools and supports are made available for trainees to maintain their skills once back to their laboratory.Really designed with the 3Rs’ principle in mind, this course should contribute to promote more reproducible and compassionate approaches in animal research in Neuroscience.Reference(s) :Vogt, C., Gervasoni, D., Grezel, D., Morales, A. (2011) ALTEX. 28 (Special Issue):218.Keywords : Alternative methods; Training program; Continuing education; Stereotactic neurosurgery; Simulatio

Formation innovante à la neurochirurgie stéréotaxique sans animaux

International audienc

INNOVATIVE ANIMAL-FREE TRAINING TO STEREOTAXIC NEUROSURGERY

International audienc

Improving Stereotaxic Neurosurgery Techniques and Procedures Greatly Reduces the Number of Rats Used per Experimental Group—A Practice Report

International audienceTechniques of stereotaxic surgery are commonly used in research laboratories by a range of students, technicians, and researchers. To meet the evolving requirements imposed by international legislation, and to promote the implementation of 3R rules (replacement, reduction, and refinement) by reducing experimental error, animal morbidity, and mortality, it is essential that standard operating procedures and proper conduct following such complex surgeries be precisely described and respected. The present report shows how refinements of our own neurosurgical techniques over decades, have significantly reduced the number of animals (rats) used in experiments and improved the animals’ well-being during the post-surgical recovery period. The current pre-, per-, and post-surgical procedures used in our laboratory are detailed. We describe the practical aspects of stereotaxic neurosurgery that have been refined in our laboratory since 1992 and that cover various areas including appropriate anesthesia and pain management during and after surgery, methods to determine the stereotaxic coordinates, and the best approach to the target brain structure. The application of these optimal surgical methods that combine reliable and reproducible results with an acute awareness of ethics and animal welfare leads to a significant reduction in the number of animals included in experimental research in accordance with ethical and regulatory rules as required by the European Directive on laboratory animal welfare

NEUROMODULATION DE L'ACTIVITE DES NEURONES MONOAMINERGIQUES AU .COURS DU CYCLE VEILLE-SOMMEIL (APPROCHES ELECTROPHYSIOLOGIQUE ET PHARMACOLOGIQUE CHEZ LE RAT VIGILE)

LYON1-BU Santé (693882101) / SudocPARIS-BIUM (751062103) / SudocPARIS-BIUP (751062107) / SudocSudocFranceF

Fast Modulation of Prefrontal Cortex Activity by Basal Forebrain Noncholinergic Neuronal Ensembles

International audienceTraditionally, most basal forebrain (BF) functions have been attributed to its cholinergic neurons. However, the majority of cortical-projecting BF neurons are noncholinergic and their in vivo functions remain unclear. We investigated how BF modulates cortical dynamics by simultaneously recording </=50 BF single neurons along with local field potentials (LFPs) from the prefrontal cortex (PFCx) in different wake-sleep states of adult rats. Using stereotypical spike time correlations, we identified a large (roughly 70%) subset of BF neurons, which we named BF tonic neurons (BFTNs). BFTNs fired tonically at 2-8 Hz without significantly changing their average firing rate across wake-sleep states. As such, these cannot be classified as cholinergic neurons. BFTNs substantially increased the spiking variability during waking and rapid-eye-movement sleep, by exhibiting frequent spike bursts with <50-ms interspike interval. Spike bursts among BFTNs were highly correlated, leading to transient population synchronization events of BFTN ensembles that lasted on average 160 ms. Most importantly, BFTN synchronization occurred preferentially just before the troughs of PFCx LFP oscillations, which reflect increased cortical activity. Furthermore, BFTN synchronization was accompanied by transient increases in prefrontal cortex gamma oscillations. These results suggest that synchronization of BFTN ensembles, which are likely to be formed by cortical-projecting GABAergic neurons from the BF, could be primarily responsible for fast cortical modulations to provide transient amplification of cortical activity