Reticular Neurons Research Articles

Gigantocellular Neurons Awaken the Brain from Deep Pharmacologically-Induced Coma

Attempts at neuromodulation using deep brain stimulation (DBS) have targeted a number of loci in brain arousal pathways such as the thalamus, mesencephalon and cervical cord. However, recovery following single location stimulation remains modest, especially in comatose patients. Although some of these pathways can trigger awakening from sleep or light planes of anesthesia upon activation are insufficient to promote arousal from a deeper arousal state like coma. Interpretation of these results suggests that to fully emerge from a deep arousal state, coordination of multiple pathways is required. The mechanism through which this coordination is achieved by the brain is poorly understood. Considering that medullary reticular neurons project to arousal- modulating areas throughout the brain, integrate a broad range of sensory and autonomic inputs, and fire in response to salient stimuli in close association with the initiation of behaviors, we modulated their activity during a pharmacologic induced coma (PIC). Our results showed that pharmacologic or optogenetic activation of an area located at the nucleus gigantocellularis (NGC)- elicited robust cortical, autonomic and motor arousal during a state of PIC. To understand how this small subpopulation of neurons exerts such widespread activational effects on arousal, we analyzed immunolabeling of c-Fos-a well-established marker of neuronal activation-following pharmacologic activation of NGC neurons. C-Fos labeling was sparse and largely limited to structures known to participate in arousal including rhombenchephalon (locus coeruleus and parabrachial nucleus); mesencephalon (periaqueductal gray and ventral tegmental area); diencephalon (intralaminar thalamic nuclei as well as posterior and anterior hypothalamus). These findings suggest that NGC is able to recruit these pathways to trigger arousal from a dense PIC. Results of this study will uncover novel mechanisms leading to new approaches for emerging treatments for patients under coma state.

Augmented Reticular Thalamic Bursting and Seizures in Scn1a-Dravet Syndrome

SUMMARYLoss of function in the Scn1a gene leads to a severe epileptic encephalopathy called Dravet syndrome (DS). Reduced excitability in cortical inhibitory neurons is thought to be the major cause of DS seizures. Here, in contrast, we show enhanced excitability in thalamic inhibitory neurons that promotes the non-convulsive seizures that are a prominent yet poorly understood feature of DS. In a mouse model of DS with a loss of function in Scn1a, reticular thalamic cells exhibited abnormally long bursts of firing caused by the downregulation of calcium-activated potassium SK channels. Our study supports a mechanism in which loss of SK activity causes the reticular thalamic neurons to become hyperexcitable and promote non-convulsive seizures in DS. We propose that reduced excitability of inhibitory neurons is not global in DS and that non-GABAergic mechanisms such as SK channels may be important targets for treatment.

The role of NLRP3 inflammasome in stroke and central poststroke pain.

Background:NLRP3 inflammasome plays a prominent role in the pathogenesis and progression of many diseases, such as type 2 diabetes mellitus, obesity, atherosclerosis, and Alzheimer's disease. However, little knowledge is known about the role of NLRP3 inflammasome in central post-stroke pain (CPSP).Methods:We selected relevant studies by searching PubMed, Embase, and Medline from inception through February, 2018. We systematically reviewed available publications according to the terms “NLRP3 inflammasome” and “stroke” or “central post-stroke pain” in the title/abstract field.Results:We reviewed the articles and put forward two possible ways for NLRP3 inflammasome in CPSP. One way is that NLRP3 activation causes cerebral cortex injure, decreasing descending projection fiber to thalamus. Such condition may let GABAergic releases reduce, making the ventral basal (VB) neurons excitability increased. Finally, CPSP occur. Another way is that NLRP3 inflammasome leads to thalamic lesion and strengthens inflammatory response of microglia at the same time. Persistent inflammation causes GABAergic alteration in thalamus reticular neurons (TRN) to restrain VB interneurons functions, contributing to CPSP.Conclusions:These possible mechanisms will help become knowledgeable about the occurrence CPSP and provide potential therapy for CPSP.

Molecular profiling of reticular gigantocellularis neurons indicates that eNOS modulates environmentally dependent levels of arousal

Neurons of the medullary reticular nucleus gigantocellularis (NGC) and their targets have recently been a focus of research on mechanisms supporting generalized CNS arousal (GA) required for proper cognitive functions. Using the retro-TRAP method, we characterized transcripts enriched in NGC neurons which have projections to the thalamus. The unique expression and activation of the endothelial nitric oxide (eNOS) signaling pathway in these cells and their intimate connections with blood vessels indicate that these neurons exert direct neurovascular coupling. Production of nitric oxide (NO) within eNOS-positive NGC neurons increases after environmental perturbations, indicating a role for eNOS/NO in modulating environmentally appropriate levels of GA. Inhibition of NO production causes dysregulated behavioral arousal after exposure to environmental perturbation. Further, our findings suggest interpretations for associations between psychiatric disorders and mutations in the eNOS locus.

Calcium-induced calcium release activates spontaneous miniature outward currents in newt medullary reticular formation neurons.

Neurons in the medullary reticular formation are involved in the control of postural and locomotor behaviors in all vertebrates. Reticulospinal neurons in this brain region provide one of the major descending projections to the spinal cord. Although neurons in the newt medullary reticular formation have been extensively studied using in vivo extracellular recordings, little is known of their intrinsic biophysical properties or of the underlying circuitry of this region. Using whole cell patch-clamp recordings in brain slices containing the rostromedial reticular formation from adult male newts, we observed spontaneous miniature outward currents (SMOCs) in ~2/3 of neurons. Although SMOCs superficially resembled inhibitory postsynaptic currents (IPSCs), they had slower risetimes and decay times than spontaneous IPSCs. SMOCs required intracellular Ca2+ release from ryanodine receptors and were also dependent on the influx of extracellular Ca2+. SMOCs were unaffected by apamin but were partially blocked by iberiotoxin and charybdotoxin, indicating that SMOCs were mediated by big-conductance Ca2+-activated K+ channels. Application of the sarco/endoplasmic Ca2+ ATPase inhibitor cyclopiazonic acid blocked the generation of SMOCs and also increased neural excitability. Neurons with SMOCs had significantly broader action potentials, slower membrane time constants, and higher input resistance than neurons without SMOCs. Thus, SMOCs may serve as a mechanism to regulate action potential threshold in a majority of neurons within the newt medullary reticular formation. NEW & NOTEWORTHY The medullary reticular formation exerts a powerful influence on sensorimotor integration and subsequent motor behavior, yet little is known about the neurons involved. In this study, we identify a transient potassium current that regulates action potential threshold in a majority of medullary reticular neurons.

The Feasibility of Encapsulated Embryonic Medullary Reticular Cells to Grow and Differentiate Into Neurons in Functionalized Gelatin-Based Hydrogels.

The study of the behavior of embryonic neurons in controlled in vitro conditions require methodologies that take advantage of advanced tissue engineering approaches to replicate elements of the developing brain extracellular matrix. We report here a series of experiments that explore the potential of photo-polymerized gelatin hydrogels to culture primary embryonic neurons. We employed large medullary reticular neurons whose activity is essential for brain arousal as well as a library of gelatin hydrogels that span a range of mechanical properties, inclusion of brain-mimetic hyaluronic acid, and adhesion peptides. These hydrogel platforms showed inherent capabilities to sustain neuronal viability and were permissive for neuronal differentiation, resulting in the development of neurite outgrowth under specific conditions. The maturation of embryonic medullary reticular cells took place in the absence of growth factors or other exogenous bioactive molecules. Immunocytochemistry labeling of neuron-specific tubulin confirmed the initiation of neural differentiation. Thus, this methodology provides an important validation for future studies of nerve cell growth and maintenance.

Classification of Neurons in the Primate Reticular Formation and Changes after Recovery from Pyramidal Tract Lesion.

The reticular formation is important in primate motor control, both in health and during recovery after brain damage. Little is known about the different neurons present in the reticular nuclei. Here we recorded extracellular spikes from the reticular formation in five healthy female awake behaving monkeys (193 cells), and in two female monkeys 1 year after recovery from a unilateral pyramidal tract lesion (125 cells). Analysis of spike shape and four measures derived from the interspike interval distribution identified four clusters of neurons in control animals. Cluster 1 cells had a slow firing rate. Cluster 2 cells had narrow spikes and irregular firing, which often included high-frequency bursts. Cluster 3 cells were highly rhythmic and fast firing. Cluster 4 cells showed negative spikes. A separate population of 42 cells was antidromically identified as reticulospinal neurons in five anesthetized female monkeys. The distribution of spike width in these cells closely overlaid the distribution for cluster 2, leading us tentatively to suggest that cluster 2 included neurons with reticulospinal projections. In animals after corticospinal lesion, cells could be identified in all four clusters. The firing rate of cells in clusters 1 and 2 was increased in lesioned animals relative to control animals (by 52% and 60%, respectively); cells in cluster 2 were also more regular and more bursting in the lesioned animals. We suggest that changes in both membrane properties and local circuits within the reticular formation occur following lesioning, potentially increasing reticulospinal output to help compensate for lost corticospinal descending drive.SIGNIFICANCE STATEMENT This work is the first to subclassify neurons in the reticular formation, providing insights into the local circuitry of this important but little understood structure. The approach developed can be applied to any extracellular recording from this region, allowing future studies to place their data within our current framework of four neural types. Changes in reticular neurons may be important to subserve functional recovery after damage in human patients, such as after stroke or spinal cord injury.

Heartless beat or beatless heart?

Recurring bursts of thalamocortical cells were thought to be indispensable in driving absence seizures. A new study demonstrates that bursts from inhibitory thalamic reticular neurons are crucial instead. Reticular bursts are driven by cortical inputs and govern precise timing of thalamocortical cell activity during seizures.

Intrathalamic Connections Shape Spindle Activity \u2014 A Modelling Study

Spindle oscillations are generated predominantly during sleep state II, through cyclical interactions between thalamocortical and reticular neurons. Inhibition from reticular cells is critical for this activity; it enables burst fring by the de-inactivation of T-type Ca2+ channels. While the effect of different channelopathies on spindling is extensively investigated, our knowledge about the role of intrathalamic connections is limited. Therefore, we explored how the connection pattern and the density of reticular inhibitory synapses affect spindle activity in a thalamic network model. With more intrareticular connections, synchronous fring of reticular cells, and intraspindle burst frequency decreased, spindles lengthened. In models with strong intrareticular inhibition spindle activity was impaired, and a sustained 6–8 Hz oscillation was generated instead. The strength of reticular innervation onto thalamocortical cells played a key role in the generation of oscillations; it determined the amount of thalamocortical cell bursts, and consequently spindle length. Focal inputs supported bursts but affected only a few cells thus barely reinforced network activity, while diffuse contacts aided bursts only when a suffcient number of reticular cells fred synchronously. According to our study, alterations in the connection pattern infuence thalamic activities and may contribute to pathological conditions, or alternatively, they serve as a compensatory mechanism.

P.2.024 - Involvement of the GluN2C subunit in the behavioral syndrome induced by non-competitive NMDA antagonists

Non-competitive NMDA receptor (NMDA-R) antagonists like ketamine, dizocilpine (MK-801) and phencyclidine (PCP) are used as pharmacological models of schizophrenia and they are also being studied as antidepressant drugs [1]. In rodents, NMDA-R antagonists induce a behavioral syndrome including hyperlocomotion, ataxia signs and stereotypies, as well as other behavioral responses like disorganization in the locomotor pattern and a decrease in the exploratory activity [2]. Previous studies proposed that PCP activates thalamo-cortical circuits after the blockade of NMDA-R in reticular thalamic GABAergic neurons [3]. Since the GluN2C subunit of NMDA-R is densely expressed in thalamus and cerebellum [4], our purpose was to study the involvement of the GluN2C subunit in the behavioral syndrome induced by ketamine, MK-801 and PCP under the working hypothesis that those effects would partly depend on the blockade of thalamo-cortical NMDA-R containing the GluN2C receptor subunit. Male adult (25-35g) wild-type (WT) and GluN2C receptor subunit knockout (KOGluN2C) mice backcrossed onto a C57BL/6J genetic background were used. Ketamine hydrochloride (Ketolar®, Pfizer), dizocilpine maleate (Sigma-Aldrich) and phencyclidine hydrochloride (Sigma-Aldrich) were dissolved in saline (PCP solution was pH adjusted to 6–6.5 with sodium bicarbonate). Ketamine (10 mg/kg, i.p.), MK-801 (0.10 and 0.25 mg/kg, i.p.) and PCP (5 mg/kg, s.c.) were injected immediately, 30 min and 15 min before behavioral testing, respectively. Mice were placed in a dimly lighted open field cage where activity was recorded with a video camera during 30 min or 2 h. Distance moved (cm) was calculated by the videotrack View Point software (France). Behavioral signs such as number of rearings, number of falls, circling and hind-limb abduction were observed and scored by an experimenter blind to mice genotype and treatment. Statistical analyses were carried out using two-way ANOVA followed by Newman-Keuls post-hoc comparisons. Data are expressed as mean ± SEM and the level of significance was set at p The administration of ketamine and MK-801 significantly enhanced locomotor activity and decreased exploratory behavior (number of rearings) similarly in both genotypes (p Overall, these results show that the GluN2C subunit appears to be strongly involved in the stereotyped behavior induced by non-competitive NMDA-R antagonists. KOGluN2C mice showed less motor impairment, as suggested by the decrease in the number of falls and the increased exploratory behavior, which may account for the genotype differences in the locomotor activity observed in PCP-treated mice. Further, the dramatic difference in the number of falls between WT and KOGluN2C mice suggests the involvement of the cerebellum, a key brain structure for the control of motor coordination.

Shank3-deficient thalamocortical neurons show HCN channelopathy and alterations in intrinsic electrical properties.

Shank3 increases the HCN channel surface expression in heterologous expression systems. Shank3Δ13-16 deficiency causes significant reduction in HCN2 expression and Ih current amplitude in thalamocortical (TC) neurons. Shank3Δ13-16 - but not Shank3Δ4-9 -deficient TC neurons share changes in basic electrical properties which are comparable to those of HCN2-/- TC neurons. HCN channelopathy may critically mediate events downstream from Shank3 deficiency. SHANK3 is a scaffolding protein that is highly enriched in excitatory synapses. Mutations in the SHANK3 gene have been linked to neuropsychiatric disorders especially the autism spectrum disorders. SHANK3 deficiency is known to cause impairments in synaptic transmission, but its effects on basic neuronal electrical properties that are more localized to the soma and proximal dendrites remain unclear. Here we confirmed that in heterologous expression systems two different mouse Shank3 isoforms, Shank3A and Shank3C, significantly increase the surface expression of the mouse hyperpolarization-activated, cyclic-nucleotide-gated (HCN) channel. In Shank3Δ13-16 knockout mice, which lack exons 13-16 in the Shank3 gene (both Shank3A and Shank3C are removed) and display a severe behavioural phenotype, the expression of HCN2 is reduced to an undetectable level. The thalamocortical (TC) neurons from the ventrobasal (VB) complex of Shank3Δ13-16 mice demonstrate reduced Ih current amplitude and correspondingly increased input resistance, negatively shifted resting membrane potential, and abnormal spike firing in both tonic and burst modes. Impressively, these changes closely resemble those of HCN2-/- TC neurons but not of the TC neurons from Shank3Δ4-9 mice, which lack exons 4-9 in the Shank3 gene (Shank3C still exists) and demonstrate moderate behavioural phenotypes. Additionally, Shank3 deficiency increases the ratio of excitatory/inhibitory balance in VB neurons but has a limited impact on the electrical properties of connected thalamic reticular (RTN) neurons. These results provide new understanding about the role of HCN channelopathy in mediating detrimental effects downstream from Shank3 deficiency.

CaV 3.2 drives sustained burst-firing, which is critical for absence seizure propagation in reticular thalamic neurons.

SummaryObjectiveGenetic alterations have been identified in the CACNA1H gene, encoding the CaV3.2 T‐type calcium channel in patients with absence epilepsy, yet the precise mechanisms relating to seizure propagation and spike‐wave‐discharge (SWD) pacemaking remain unknown. Neurons of the thalamic reticular nucleus (TRN) express high levels of CaV3.2 calcium channels, and we investigated whether a gain‐of‐function mutation in the Cacna1h gene in Genetic Absence Epilepsy Rats from Strasbourg (GAERS) contributes to seizure propagation and pacemaking in the TRN.MethodsPathophysiological contributions of CaV3.2 calcium channels to burst firing and absence seizures were assessed in vitro using acute brain slice electrophysiology and quantitative real‐time polymerase chain reaction (PCR) and in vivo using free‐moving electrocorticography recordings.Results TRN neurons from GAERS display sustained oscillatory burst‐firing that is both age‐ and frequency‐dependent, occurring only in the frequencies overlapping with GAERS SWDs and correlating with the expression of a CaV3.2 mutation‐sensitive splice variant. In vivo knock‐down of CaV3.2 using direct thalamic injection of lipid nanoparticles containing CaV3.2 dicer small interfering (Dsi) RNA normalized TRN burst‐firing, and in free‐moving GAERS significantly shortened seizures.SignificanceThis supports a role for TRN CaV3.2 T‐type channels in propagating thalamocortical network seizures and setting the pacemaking frequency of SWDs.

Modeling pathogenesis and treatment response in childhood absence epilepsy.

Childhood absence epilepsy (CAE) is a genetic generalized epilepsy syndrome with polygenic inheritance, with genes for γ-aminobutyric acid (GABA) receptors and T-type calcium channels implicated in the disorder. Previous studies of T-type calcium channel electrophysiology have shown genetic changes and medications have multiple effects. The aim of this study was to use an established thalamocortical computer model to determine how T-type calcium channels work in concert with cortical excitability to contribute to pathogenesis and treatment response in CAE. The model is comprised of cortical pyramidal, cortical inhibitory, thalamocortical relay, and thalamic reticular single-compartment neurons, implemented with Hodgkin-Huxley model ion channels and connected by AMPA, GABAA , and GABAB synapses. Network behavior was simulated for different combinations of T-type calcium channel conductance, inactivation time, steady state activation/inactivation shift, and cortical GABAA conductance. Decreasing cortical GABAA conductance and increasing T-type calcium channel conductance converted spindle to spike and wave oscillations; smaller changes were required if both were changed in concert. In contrast, left shift of steady state voltage activation/inactivation did not lead to spike and wave oscillations, whereas right shift reduced network propensity for oscillations of any type. These results provide a window into mechanisms underlying polygenic inheritance in CAE, as well as a mechanism for treatment effects and failures mediated by these channels. Although the model is a simplification of the human thalamocortical network, it serves as a useful starting point for predicting the implications of ion channel electrophysiology in polygenic epilepsy such as CAE.

Systematic Morphometry of Catecholamine Nuclei in the Brainstem.

Catecholamine nuclei within the brainstem reticular formation (RF) play a pivotal role in a variety of brain functions. However, a systematic characterization of these nuclei in the very same experimental conditions is missing so far. Tyrosine hydroxylase (TH) immune-positive cells of the brainstem correspond to dopamine (DA)-, norepinephrine (NE)-, and epinephrine (E)-containing cells. Here, we report a systematic count of TH-positive neurons in the RF of the mouse brainstem by using stereological morphometry. All these nuclei were analyzed for anatomical localization, rostro-caudal extension, volume, neuron number, neuron density, and mean neuronal area for each nucleus. The present data apart from inherent informative value wish to represent a reference for neuronal mapping in those studies investigating the functional anatomy of the brainstem RF. These include: the sleep-wake cycle, movement control, muscle tone modulation, mood control, novelty orienting stimuli, attention, archaic responses to internal and external stressful stimuli, anxiety, breathing, blood pressure, and innumerable activities modulated by the archaic iso-dendritic hard core of the brainstem RF. Most TH-immune-positive cells fill the lateral part of the RF, which indeed possesses a high catecholamine content. A few nuclei are medial, although conventional nosography considers all these nuclei as part of the lateral column of the RF. Despite the key role of these nuclei in psychiatric and neurological disorders, only a few of them aspired a great attention in biomedical investigation, while most of them remain largely obscure although intense research is currently in progress. A simultaneous description of all these nuclei is not simply key to comprehend the variety of brainstem catecholamine reticular neurons, but probably represents an intrinsically key base for understanding brain physiology and physiopathology.

Shaping somatosensory responses in awake rats: cortical modulation of thalamic neurons.

Massive corticothalamic afferents originating from layer 6a of primary sensory cortical areas modulate sensory responsiveness of thalamocortical neurons and are pivotal for shifting neuronal firing between burst and tonic modes. The influence of the corticothalamic pathways on the firing mode and sensory gain of thalamic neurons has only been extensively examined in anesthetized animals, but has yet to be established in the awake state. We made lesions of the rat barrel cortex and on the following day recorded responses of single thalamocortical and thalamic reticular neurons to a single vibrissal deflection in the somatosensory system during wakefulness. Our results showed that the cortical lesions shifted the response of thalamic neurons towards bursting, elevated the response probability and the gain of thalamocortical neurons, predominantly of recurring responses. In addition, after the lesions, the spontaneous activities of the vibrissa-responsive thalamic neurons, but not those of vibrissa-unresponsive cells, were typified by waxing-and-waning spindle-like rhythmic spiking with frequent bursting. In awake rats with intact cortex, identified layer 6a corticothalamic neurons responded to a single vibrissal deflection with short latencies that matched those of layer 4 neurons, strongly suggesting the existence of an immediate corticothalamic feedback. The present results show the importance of corticothalamic neurons in shaping thalamic activities during wakefulness.

Spatial scale of receptive fields in the visual sector of the cat thalamic reticular nucleus

Inhibitory projections from the visual sector of the thalamic reticular nucleus to the lateral geniculate nucleus complete the earliest feedback loop in the mammalian visual pathway and regulate the flow of information from retina to cortex. There are two competing hypotheses about the function of the thalamic reticular nucleus. One regards the structure as a thermostat that uniformly regulates thalamic activity through negative feedback. Alternatively, the searchlight hypothesis argues for a role in focal attentional modulation through positive feedback, consistent with observations that behavioral state influences reticular activity. Here, we address the question of whether cells in the reticular nucleus have receptive fields small enough to provide localized feedback by devising methods to quantify the size of these fields across visual space. Our results show that reticular neurons in the cat operate over discrete spatial scales, at once supporting the searchlight hypothesis and a role in feature selective sensory processing.

Organization of alpha-transducin immunoreactive system in the brain and retina of larval and young adult Sea Lamprey (Petromyzon marinus), and their relationship with other neural systems.

We employed an anti-transducin antibody (Gαt-S), in combination with other markers, to characterize the Gαt-S-immunoreactive (ir) system in the CNS of the sea lamprey, Petromyzon marinus. Gαt-S immunoreactivity was observed in some neuronal populations and numerous fibers distributed throughout the brain. Double Gαt-S- and opsin-ir neurons (putative photoreceptors) are distributed in the hypothalamus (postoptic commissure nucleus, dorsal and ventral hypothalamus) and caudal diencephalon, confirming results of García-Fernández et al. (Cell and Tissue Research, 288, 267-278, 1997). Singly Gαt-S-ir cells were observed in the midbrain and hindbrain, increasing the known populations. Our results reveal for the first time in vertebrates the extensive innervation of many brain regions and the spinal cord by Gαt-S-ir fibers. The Gαt-S innervation of the habenula is very selective, fibers densely innervating the lamprey homologue of the mammalian medial nucleus (Stephenson-Jones et al., Proceedings of the National Academy of Sciences of the United States of America, 109, E164-E173, 2012), but not the lateral nucleus homologue. The lamprey neurohypophysis was not innervated by Gαt-S-ir fibers. We also analyzed by double immunofluorescence the relation of this system with other systems. A dopaminergic marker (TH), serotonin (5-HT) or GABA do not co-localize with Gαt-S-ir neurons although codistribution of fibers was observed. Codistribution of Gαt-S-ir fibers and isolectin-labeled extrabulbar primary olfactory fibers was observed in the striatum and hypothalamus. Neurobiotin retrograde transport from the spinal cord combined with immunofluorescence revealed spinal-projecting Gαt-S-ir reticular neurons in the caudal hindbrain. Present results in an ancient vertebrate reveal for the first time a collection of brain targets of Gαt-S-ir neurons, suggesting they might mediate non-visual modulation by light in many systems.

S72 Cortical feedback and thalamocortical activity

Though the thalamus is generally regarded as the gateway to the neocortex, information flow is not unidirectional, as layer 6. of the cortex provides massive glutamatergic feedback to the thalamus. It has a possible role in selective attention, sleep oscillations, and may even act as a classical modulatory pathway, nevertheless the overall picture is still murky. To probe this system, we used NTSR1-ChR mice, a strain expressing channelrhodospin in L6 corticothalamic cells selectively, paired with multichannel silicon probe recordings. At the single cell level we found a combination of excitation and inhibition on thalamocortical, while only excitation on thalamic reticular neurons. The excitation-inhibition profile was dependent on stimulation strength, as well as the network state. At the network level, L6 elicited spindles in a fashion similar to direct nRT activation. Namely, no spindles could be evoked during deeply synchronized and desynchronized network states, only during light synchronization, a state analogous to stage 2. sleep, in which spontaneous spindles also appear. Prolonged activation of the corticothalamic feedback often changed the network state, supporting the role of L6 as a modulatory system.

S113 The thalamo-cortical system as central actor of NREM sleep

Neuronal activity in several brain regions is state dependent. This is best exemplified by the dramatic changes that occur in the electroencephalogram as states of vigilance transition from waking to sleep leading to brain waves of various frequencies. The main generator of these state dependent rhythmic activities is the thalamocortical system, a reciprocally interconnected network consisting of thalamocortical relay neurons, two types of thalamic inhibitory neurons including thalamic reticular neurons and local circuit interneurons and various neocortical principal cells and inhibitory interneurons. In the absence of sensory inputs, as happens during sleep and relaxed wakefulness neurons in the thalamus and neocortex engage in stereotyped rhythmic activity patterns spanning a wide range of frequencies, including slow waves, d-waves and sleep spindles. The generation of these rhythms is governed by an interplay between spatially and temporally coordinated synaptic interactions and intrinsic membrane properties of various thalamic and cortical neurons. Thalamic involvement in NREM sleep rhythms relies on a peculiar intrinsic cellular substrate of thalamic burst firing, the low-threshold Ca2+ spike. Cortico-thalamo-cortical synaptic interactions fine tune these intrinsic activity patterns to generate the plethora of state-dependent rhythmic activities.

Distribution and Function of the Bestrophin-1 (Best1) Channel in the Brain.

Bestrophin-1 (Best1) is a calcium-activated anion channel identified from retinal pigment epithelium where human mutations are associated with Best's macular degeneration. Best1 is known to be expressed in a variety of tissues including the brain, and is thought to be involved in many physiological processes. This review focuses on the current state of knowledge on aspects of expression and function of Best1 in the brain. Best1 protein is observed in cortical and hippocampal astrocytes, in cerebellar Bergmann glia and lamellar astrocytes, in thalamic reticular neurons, in meninges and in the epithelial cells of the choroid plexus. The most prominent feature of Best1 is its significant permeability to glutamate and GABA in addition to chloride ions because glutamate and GABA are important transmitters in the brain. Under physiological conditions, both Best1-mediated glutamate release and tonic GABA release from astrocytes modulate neuronal excitability, synaptic transmission and synaptic plasticity. Under pathological conditions such as neuroinflammation and neurodegeneration, reactive astrocytes phenotypically switch from GABA-negative to GABA-producing and redistribute Best1 from the perisynaptic microdomains to the soma and processes to tonically release GABA via Best1. This implicates that tonic GABA release from reactive astrocyte via redistributed Best1 is a common phenomenon that occur in various pathological conditions with astrogliosis such as traumatic brain injury, neuroinflammation, neurodegeneration, and hypoxic and ischemic insults. These properties of Best1, including the permeation and release of glutamate and GABA and its redistribution in reactive astrocytes, promise us exciting discoveries of novel brain functions to be uncovered in the future.