Neuroscience

The suprachiasmatic nucleus (SCN) is believed to contain the main generator of circadian rhythmicity in mammals. In order to obtain further functional details of this, electrophysiological extracellular measurements in vitro were made. By means of an interspike interval distribution analysis, it is shown that there is a novel kind of neuronal firing pattern: the harmonic pattern. From these observations, we have developed a theoretical model based on possible filtering processes occurring during synaptic transmission. The model suflices to infer that regular ultradian oscillators could be an emergent property of circuit interactions of cells in the suprachiasmatic nucleus.

Water-homeostasis is a fundamental physiological process for terrestrial life. In vertebrates, thirst drives water intake, but the neuronal circuits that connect the physiology of water regulation with emotional context are poorly understood. Vasopressin (VP) is a prominent messenger in this circuit, as well as L-glutamate. We have investigated the role of a VP circuit and interaction between thirst and motivational behaviors evoked by life-threatening stimuli in rats. We demonstrate a direct pathway from hypothalamic paraventricular VP-expressing, glutamatergic magnocellular neurons to the medial division of lateral habenula (LHbM), a region containing GABAergic neurons. In vivo recording and juxtacellular labeling revealed that GABAergic neurons in the LHbM had locally branching axons, and received VP-positive axon terminal contacts on their dendrites. Water deprivation significantly reduced freezing and immobility behaviors evoked by innate fear and behavioral despair, respectively, accompanied by decreased Fos expression in the lateral habenula. Our results reveal a novel VP-expressing hypothalamus to the LHbM circuit that is likely to evoke GABA-mediated inhibition in the LHbM, which promotes escape behavior during stress coping.

Building on recent interest in the convergence of arts and sciences, we propose specific areas of intersection between the disciplines of Bharatanatyam, a classical Indian dance, and neuroscience. We present personal reflections by practitioners of both disciplines and propose that Bharatanatyam can be used to understand and explain brain functioning and that neuroscience can help analyze the dancing Bharatanatyam brain. We explore conceptual areas of convergence between the two fields as well as specific points of connection using language acquisition, rhythm, music, and cognition as examples. We conjecture that Bharatanatyam training and practice support long-term neuronal plasticity in various parts of the brain, including but not limited to the hippocampus, motor, premotor cortex, and the cerebellum. The beginning of the study of the intersection between these disciplines will pave the way for additional allied fields of rich thinking, exploration and potentially, therapy.

Building on recent interest in the convergence of arts and sciences, we propose specific areas of intersection between the disciplines of Bharatanatyam, a classical Indian dance, and neuroscience. We present personal reflections by practitioners of both disciplines and propose that Bharatanatyam can be used to understand and explain brain functioning and that neuroscience can help analyze the dancing Bharatanatyam brain. We explore conceptual areas of convergence between the two fields as well as specific points of connection using language acquisition, rhythm, music, and cognition as examples. We conjecture that Bharatanatyam training and practice support long-term neuronal plasticity in various parts of the brain, including but not limited to the hippocampus, motor, premotor cortex, and the cerebellum. The beginning of the study of the intersection between these disciplines will pave the way for additional allied fields of rich thinking, exploration and potentially, therapy.

Introduction: Nuclear medicine services, though still an emerging area in the field of medicine in Nigeria, have not been optimally utilised, possibly due to a lack of awareness by health workers. This study evaluated the knowledge and awareness of pharmacists and patients regarding radiopharmaceutical use in disease management. Methods: In this cross-sectional survey in southwest Nigeria, online self-administered and interviewer-administered structured questionnaires were used to collect data on the knowledge and perception of radiopharmaceuticals from 343 pharmacists and 67 ambulatory patients. The influence of the participant's socio-demographic characteristics on the knowledge of radiopharmaceuticals scores was assessed with Man-Whitney U and Kruskal Wallis tests at p < 0.05. Results: The study found that 191 (55.7%) pharmacists and 75 (98.7%) patients had good knowledge of radiopharmaceuticals, while 70 (21.3%) pharmacists knew radiopharmaceuticals are regulated as radioactive substances and drugs. Most patients, 47 (61.8%), knew how to prevent radiation exposure to others, and 68 (89.5%) believed radiopharmaceuticals would help disease management. Conclusion: Pharmacists and patients have good knowledge of the use of radiopharmaceuticals. Pharmacists' knowledge was influenced by the state of practice and prior knowledge of radiopharmaceuticals, while the number of clinics attended influenced patients' knowledge.

A key player in olfactory processing is the olfactory bulb (OB) mitral cell (MC). We have used dual whole-cell patch-clamp recordings from the apical dendrite and cell soma of MCs to develop a passive compartmental model based on detailed morphological reconstructions of the same cells. Matching the model to traces recorded in experiments we find: C m = 1.91 ± 0.20 μF cm -2 , R m = 3547 ± 1934 cm 2 and R i = 173 ± 99 cm. We have constructed a six MC gap-junction (GJ) network model of morphologically accurate MCs. These passive parameters (PPs) were then incorporated into the model with Na + , Kdr, and KA conductances and GJs from . The GJs were placed in the apical dendrite tuft (ADT) and their conductance adjusted to give a coupling ratio between MCs consistent with experimental findings (∼0.04). Firing at ∼50 Hz was induced in all six MCs with continuous current injections (0.05-0.07 nA) at 20 locations to the ADT of two of the MCs. It was found that MCs in the network synchronized better when they shared identical PPs rather than using their own PPs for the fit suggesting that the OB may have populations of MCs tuned for synchrony. The addition of calcium-activated potassium channels (iKCa) and L-type calcium channels (iCa(L)) to the model enabled MCs to generate burst firing. However, the GJ coupling was no longer sufficient to synchronize firing. When cells were stimulated by a continuous current injection there was an initial period of asynchronous burst firing followed after ∼120 ms by synchronous repetitive firing. This occurred as intracellular calcium fell due to reduced iCa(L) activity. The kinetics of one of the iCa(L) gate variables, which had a long activation time constant (τ ∼ range 18-150 ms), was responsible for this fall in iCa(L). The model makes predictions about the nature of the kinetics of the calcium current that will need experimental verification.

The olfactory bulb is located at the start of a hierarchical chain of sensory processing mechanisms. The relative ease of its isolation allows the possibility that models of these mechanisms might be integrated to develop a detailed understanding of function. In this sensory processing chain odour molecules evoke signal transduction in the olfactory receptor neurons. These signals represent the diverse range of molecular binding affinities of the olfactory receptor proteins. The first level of processing of this sensory input is performed by the neurons of the olfactory bulb. The olfactory system needs to filter the vast amount of sensory input it receives to be able to select the subset of biological significance. The importance of the olfactory bulb in this filtering process is suggested by its wide range of modulatory mechanisms. These mechanisms include an array of centrifugal inputs from other regions of the brain as well as numerous intrinsic feedback circuits. Given the complexity of the olfactory bulb and the range of its modulatory activity, the process of isolation of its components produces some difficulties of interpretation. This is mainly due to the removal of some of the effects of interaction and the change in balance that results. We present a summary of the current understanding of the interacting modulatory elements that are found in the olfactory bulb and a detailed account of the properties of mitral/tufted cells, the projection neurons of the olfactory bulb. This is followed by a discussion of the intrinsic and extrinsic modulatory systems acting on these cells. A consideration of the integration of the effects of these modulatory systems allows an understanding of how the output of the mitral/tufted cells is controlled. While significant progress has been made in the elucidation of the individual components as a result of advances in techniques over the last decade we suggest that there is a need for computational studies as a further aid to the understanding and interpretation of the weight of individual modulatory components in this dynamic interacting system.

Introduction. The number of patients with face trauma is increasing rapidly because of spreading of aggressions and other forms of violence in urban setting. The objective of our work is to describe the epidemiological considerations and the management of the isolated trauma of the face in Conakry. Methodology. This was a prospective, descriptive, 12-month study that covered all patients admitted to the Ignace Deen National Hospital for facial trauma during this period. We were interested in sociodemographic data, aetiologies, clinical findings, type of lesions and management procedures. Results. Among 2824 patients received during our study period, 139 had isolated facial trauma (of 4.92%). The age group 21-30 years was the most affected (n = 62 -44.6%) and the mean age was 28.6 years ± 4.5 years (extremes: 1 – 63). Men accounted for 78.4% of cases. Brawls and aggressions were the most frequent etiologies (n = 66, 47.5%) and facial tumefaction was the overwhelming reason for consul...

Background: Alzheimer's disease has become a growing socio-economical concern in developing countries where increased life expectancy is leading to large aged populations. While curing Alzheimer's disease or stopping its progression does not appear within reach in a foreseeable future, new therapies capable of delaying the pathogenesis would represent major breakthroughs. Presentation of the hypothesis: The growing number of medical benefits of cannabinoids, such as their ability to regulate age-related processes like neuroinflammation, neurogenesis and memory, raise the question of their potential role as a preventive treatment of AD. Testing the hypothesis: To test this hypothesis, epidemiological studies on long term, chronic cannabinoid users could enlighten us on the potential benefits of these compounds in normal and pathological ageing processes. Systematic pharmacological (and thus more mechanistic) investigations using animal models of Alzheimer's disease that have been developed would also allow a thorough investigation of the benefits of cannabinoid pharmacotherapy in the pathogenesis of Alzheimer's disease. The chronic administration of non-selective cannabinoids may delay the onset of cognitive deficits in AD patients; this will dramatically reduce the socio-economic burden of AD and improve the quality of life of the patients and their families.

With an onset under the age of 3 years, autism spectrum disorders (ASDs) are now understood as diseases arising from pre-and/or early postnatal brain developmental anomalies and/or early brain insults. To unveil the molecular mechanisms taking place during the misshaping of the developing brain, we chose to study cells that are representative of the very early stages of ontogenesis, namely stem cells. Here we report on MOlybdenum COfactor Sulfurase (MOCOS), an enzyme involved in purine metabolism, as a newly identified player in ASD. We found in adult nasal olfactory stem cells of 11 adults with ASD that MOCOS is downregulated in most of them when compared with 11 age-and gender-matched control adults without any neuropsychiatric disorders. Genetic approaches using in vivo and in vitro engineered models converge to indicate that altered expression of MOCOS results in neurotransmission and synaptic defects. Furthermore, we found that MOCOS misexpression induces increased oxidative-stress sensitivity. Our results demonstrate that altered MOCOS expression is likely to have an impact on neurodevelopment and neurotransmission, and may explain comorbid conditions, including gastrointestinal disorders. We anticipate our discovery to be a fresh starting point for the study on the roles of MOCOS in brain development and its functional implications in ASD clinical symptoms. Moreover, our study suggests the possible development of new diagnostic tests based on MOCOS expression, and paves the way for drug screening targeting MOCOS and/or the purine metabolism to ultimately develop novel treatments in ASD.

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Background Alzheimer&#39;s disease has become a growing socio-economical concern in developing countries where increased life expectancy is leading to large aged populations. While curing Alzheimer&#39;s disease or stopping its progression does not appear within reach in a foreseeable future, new therapies capable of delaying the pathogenesis would represent major breakthroughs. Presentation of the hypothesis The growing number of medical benefits of cannabinoids, such as their ability to regulate age-related processes like neuroinflammation, neurogenesis and memory, raise the question of their potential role as a preventive treatment of AD. Testing the hypothesis To test this hypothesis, epidemiological studies on long term, chronic cannabinoid users could enlighten us on the potential benefits of these compounds in normal and pathological ageing processes. Systematic pharmacological (and thus more mechanistic) investigations using animal models of Alzheimer&#39;s disease that have...

Background: Posttraumatic nerve repair and prevention of muscle atrophy represent a major challenge in restorative medicine. Considerable interest exists in the potential therapeutic value of laser phototherapy for restoring or temporary preventing denervated muscle atrophy as well as enhancing regeneration of severely injured peripheral nerve. Methods: I-Muscle and Peripheral Nerve Experimental Studies: low power laser irradiation (laser phototherapy) was applied for treatment of rat denervated muscle in order to estimate the biochemical transformation at cellular and tissue levels, as well as in a rat sciatic nerve model after crush injury, direct anastomosis and neurotube reconstruction. II-Intraoperative Clinical Study: following microsurgical release and neurolysis the nerve was subjected to direct laser irradiation using fiber optics. III-Clinical double-blind, placebo-controlled randomized study: based on the outcome of the animal trials, a clinical trial, which measured the effectiveness of 780-nm laser phototherapy on patients suffering from incomplete peripheral nerve injuries for 6 months up to several years, was designed. Results: Experimental model of denervated muscle: the animal study suggested that function of denervated muscles was partially preserved by temporary prevention of denervation-induced biochemical changes. The function of denervated muscles was restored, not completely but to a very substantial degree, by laser treatment, initiated at the earliest possible stage post-injury. Experimental peripheral nerve injury: laser phototherapy had an immediate protective effect, maintained functional activity of the injured nerve, decreased scar tissue formation at the injury site, decreased degeneration in corresponding motor neurons of the spinal cord and significantly increased axonal growth and myelinization. Intraoperative clinical study: direct laser irradiation was shown to improve functional activity of the surgically treated nerve. Clinical, double-blind, placebo-controlled randomized pilot study: in patients with incomplete long-term peripheral nerve injury, it was demonstrated that 780-nm laser irradiation progressively improved peripheral nerve function, which lead to significant functional recovery. Conclusions: Laser phototherapy temporarily preserves the function of a denervated muscle and accelerates and enhances axonal growth and regeneration after peripheral nerve injury or reconstructive procedures. Animal and clinical studies have both demonstrated the promoting action of phototherapy on peripheral nerve regeneration, which makes it possible to suggest that the time for broader clinical trials has come.

Social cognitive neuroscience is beginning to unravel a neuroanatomy of social cognition, networks of brain regions especially involved in social cognition and social functioning. It is widely acknowledged that social functioning and social cognition are impaired in attention‐deficit hyperactivity disorder (ADHD). Although an impressive amount of neuroscientific research has been conducted in ADHD, little effort has been made to link those deficits in social cognition and functioning to the well‐known brain abnormalities detected in structural and functional neuroimaging studies. We review seven functional and magnetic resonance studies conducted at our laboratory in ADHD samples during the last 5 years in order to scrutinize whether the putative neuroanatomic regions underpinning social cognition are affected in ADHD. The orbitofrontal cortex (OFC), the caudate nucleus, the ventral striatum, and the cerebellum are among those regions that displayed functional or morphometric abnorm...

Migraine is a neurological disorder characterized by episodes of severe headache. Cortical spreading depression (CSD), the electrophysiological equivalent of migraine aura, results in opening of pannexin-1 megachannels that release ATP and triggers parenchymal neuroinflammatory signaling cascade in the cortex. Migraine symptoms suggesting subcortical dysfunction bring subcortical spread of CSD under the light. Here, we investigated the role of purinergic P2X7 receptors on the subcortical spread of CSD and its consequent neuroinflammation using a potent and selective P2X7 antagonist, JNJ-47965567. P2X7 antagonism had no effect on the CSD threshold and characteristics but increased the latency to hypothalamic voltage deflection following CSD showing that ATP acts as a mediator in the subcortical spread. P2X7 antagonism also prevented hypothalamic neuronal activation following CSD, revealed by bilateral decrease in hypothalamic c-fos positive neuron count. P2X7 antagonism further stopp...

During peripheral tissue inflammation, inflammatory processes in the CNS can be initiated by bloodborne pro-inflammatory mediators. The choroid plexus, the site of CSF production, is a highly specialized interface between the vascular system and CNS, and thus, this structure may be an important element in communication between the vascular compartment and the CNS during peripheral tissue inflammation. We investigated the potential participation of the choroid plexus in this process during peripheral tissue inflammation by examining expression of the SCYA2 gene which codes for monocyte chemoattractant protein-1 (MCP-1). MCP-1 protein was previously reported to be induced in a variety of cells during peripheral tissue inflammation. In the basal state, SCYA2 is highly expressed in the choroid plexus as compared to other CNS tissues. During hind paw inflammation, SCYA2 expression was significantly elevated in choroid plexus, whereas it remained unchanged in a variety of brain regions. The SCYA2-expressing cells were strongly associated with the choroid plexus as vascular depletion of blood cells by whole-body saline flush did not significantly alter SCYA2 expression in the choroid plexus. In situ hybridization suggested that the SCYA2-expressing cells were localized to the choroid plexus stroma. To elucidate potential molecular mechanisms of SCYA2 increase, we examined genes in the NF-κβ signaling cascade including TNF-α, IL-1β and IκBα in choroid tissue. Given that we also detected increased levels of MCP-1 protein by ELISA, we sought to identify potential downstream targets of MCP-1 and observed altered expression levels of mRNAs encoding tight junction proteins TJP2 and claudin 5. Finally, we detected a substantial up-regulation of the transcript encoding E-selectin, a molecule which could participate in leukocyte recruitment to the choroid plexus along with MCP-1. Together, these results suggest that profound changes occur in the choroid plexus during peripheral tissue inflammation, likely initiated by blood-borne inflammatory mediators, which may modify events in CNS.

A recent decision by the New Jersey Supreme Court has led to improved jury instructions that incorporate psychological research documenting that memory does not operate like a video recording. Here we consider how cognitive neuroscience could contribute to addressing memory in the courtroom. We discuss conditions in which neuroimaging can distinguish true and false memories in the laboratory, and note reasons to be skeptical about its use in courtroom cases. We also discuss neuroscience research concerning false and imagined memories, misinformation effects, and reconsolidation phenomena that may enhance understanding of why memory does not operate like a video recording.

Neurogenesis is sustained throughout life in the mammalian brain, supporting hippocampus-dependent learning and memory. Its permanent alteration by status epilepticus (SE) is associated with learning and cognitive impairments. The mechanisms underlying the initiation of altered neurogenesis after SE are not understood. GFAP-positive radial glia (RG) -like cells proliferate early after SE, but their proliferation dynamics and signaling are largely unclear. We have previously reported a polarized distribution of AMPA receptors (AMPARs) on RG-like cells in-vivo and postulated that these may signal their proliferation. Here, we examined the acute effects of kainate on hippocampal precursor cells in-vitro and in kainate-induced SE on proliferating and quiescent clones of BrdU pre-labelled hippocampal precursors in-vivo. In-vitro, we found that 5 µM kainate shortened the cell cycle time of RG-like cells via AMPAR activation and accelerated cell cycle re-entry of their progeny. It also shifted their fate choice expanding the population of RG-like cells and reducing the population of downstream amplifying neural progenitors. Kainate enhanced the survival of all precursor cell subtypes. Pharmacologically, kainate's proliferative and survival effects were abolished by AMPAR blockade. Functional AMPAR expression was confirmed on RG-like cells invitro. In agreement with these observations, kainate/seizures enhanced the proliferation and expansion predominantly of constitutively cycling RG-like cell clones in-vivo. Our results identify AMPARs as key potential players in initiating the proliferation of dentate RG-like cells and unravel a possible receptor target for modifying the radial glia-like cell response to SE.

IntroductionPunishment is a powerful drive that fosters aversive motivation and increases negative affect. Previous studies have reported that this drive has the propensity to improve cognitive control, as shown by improved conflict processing when it is used. However, whether aversive motivation per se or negative affect eventually drives this change remains unclear because in previous work, the specific contribution of these two components could not be isolated.MethodsTo address this question, we conducted two experiments where we administered the confound minimized Stroop task to a large group of participants each time (N = 50 and N = 47 for Experiment 1 and 2, respectively) and manipulated punishment and feedback contingency using a factorial design. These two experiments were similar except that in the second one, we also measured awareness of feedback contingency at the subjective level. We reasoned that cognitive control would improve the most when punishment would be used, a...

Mercury is a toxic heavy metal that constitutes a significant environmental and health problem, with evidences indicating the central nervous system as the main target. This study was therefore designed to evaluate the effect of caffeine on the histology of the cerebellum of mercury treated Wistar rats. Twenty adult male Wistar rats were distributed into four groups (n=4). Administration was as follows: Control (distilled water, 1 ml/kg), mercury chloride (HgCl2), 16.6 mg/kg body weight, low dose caffeine (20.7 mg/kg) with mercury chloride (16.6 mg/kg), high dose caffeine (41.5 mg/kg) with mercury chloride (16.6 mg/kg). The administrations lasted for 28 days via oral route daily. Histological evaluation was carried out with haematoxylin and eosin, and cresyl violet stains. Beam walking test (BWT) for motor coordination was carried out. Alteration in the cerebellar cortex histoarchitecture seen in mercury chloride group was ameliorated in the groups treated with caffeine. The result ...

Synphilin-1 is a cytoplasmic protein with unclear function. Synphilin-1 has been identified as an interaction partner of α-synuclein. The interaction between synphilin-1 and α-synuclein has implications in Parkinson's disease. In this study, we stably overexpressed human synphilin-1 in mouse N1E-115 neuroblastoma cells. We found that overexpression of synphilin-1 shortened cell growth doubling time and increased neurite outgrowth. Knockdown of endogenous synphilin-1 caused neuronal toxicity and shortened neurite outgrowth. We further found that synphilin-1 increased activation of the extracellular signal-regulated kinases (ERK1/2) and mediated neurite outgrowth. Rotenone, mitochondrial complex I inhibitor, has been shown previously to induce dopaminergic neurodegeneration and Parkinsonism in rats and Drosophila. We found that Rotenone induced apoptotic cell death in N1E-115 cells via caspase-3 activation and PARP cleavage. Overexpression of synphilin-1 significantly reduced Rotenone-induced cell death, caspase-3 activation and PARP cleavage. The results indicate that synphilin-1 displays trophic and protective effects in vitro, suggesting that synphilin-1 may play a protective role in PD pathogenesis and may lead to a potential therapeutic target for PD intervention.

Analog signaling describes the use of graded voltage changes as signals in the axonal compartment. Analog signaling has been described originally in invertebrates but more recent work has established its presence in the mammalian brain . In recent years, many different groups have contributed to the understanding of the physiological significance of analog signaling from a cellular perspective (for a recent review the reader may take a look at the work by Zbili and Debanne, 2019 in this Frontiers in Neuroscience Special Issue). The great majority of the experimental work related to analog signaling, however, concerns the propagation of subthreshold voltage changes from the soma to the axon. Much less attention has been paid to the propagation of subthreshold voltage changes in the opposite direction, from the axon to the soma, or to the propagation of local signals within the axon. In this mini review we will describe these other variants of analog signaling that we call here "antidromic" coupling and "local" coupling.

Recent evidence indicates the presence of presynaptic GABA A receptors (GABA A Rs) in the axon domain of several classes of central neurons, including cerebellar basket and stellate cells. Here, we investigate the possibility that these receptors could be activated in the absence of electrical or chemical stimulation. We find that low concentrations of GABA increase the frequency of miniature GABAergic synaptic currents. Submaximal concentrations of a GABA A R blocker, gabazine, decrease both the miniature current frequency and the probability of evoked GABA release. Zolpidem, an agonist of the benzodiazepine binding site, and NO-711 (1-[2-[[(diphenylmethylene)imino]oxy]ethyl]-1,2,5,6-tetrahydro-3-pyridinecarboxylic acid hydrochloride), a blocker of GABA uptake, both increase the frequency of miniature currents. These effects occur up to postnatal day 14, but not later. Immunohistochemistry indicates the presence of ␣1-containing GABA A Rs in interneuron presynaptic terminals with a similar age dependence. We conclude that, under resting conditions, axonal GABA A Rs are significantly activated, that this activation results in enhanced GABA release, and that it can be augmented by increasing the affinity of GABA A Rs or reducing GABA uptake. Our findings suggest the existence of a positive-feedback mechanism involving presynaptic GABA A Rs that maintains a high release rate and a high local GABA concentration in the immature cerebellar network.

Axons are equipped with the digital signaling capacity by which they generate and faithfully propagate action potentials (APs), and also with the analogue signaling capacity by which subthreshold activity in dendrites and soma is transmitted down the axon. Despite intense work, the extent and physiological role for subthreshold synaptic activity reaching the presynaptic boutons has remained elusive because of the technical limitation to record from them. To address this issue, we made simultaneous patch-clamp recordings from the presynaptic varicosities of cerebellar GABAergic interneurons together with their parent soma or postsynaptic target cells in young rat slices and/or primary cultures. Our tour-de-force direct functional dissection indicates that the somatodendritic spontaneous excitatory synaptic potentials are transmitted down the axon for significant distances, depolarizing presynaptic boutons. These analogously transmitted excitatory synaptic potentials augment presynaptic Ca ++ influx upon arrival of an immediately following AP through a mechanism that involves a voltage-dependent priming of the Ca ++ channels, leading to an increase in GABA release, without any modification in the presynaptic AP waveform or residual Ca ++ . Our work highlights the role of the axon in synaptic integration.

Laser photolysis to release GABA at precisely defined times and locations permits investigation of the distribution of functional GABA A receptors in neuronal compartments, the activation kinetics and pharmacology of GABA A receptors in situ, and the role of individual neurons in neural circuits by selective silencing with low GABA concentrations. We describe the experimental evaluation and applications of a new nitroindoline-caged GABA, DPNI-GABA, modified to minimize the pharmacological interference commonly found with caged GABA reagents, but retaining the advantages of nitroindoline cages. Unlike the 5-methoxycarbonylmethyl-7-nitroindolinyl-GABA tested previously, DPNI-GABA inhibited GABA A receptors with much lower affinity, reducing peak GABA-evoked responses with an IC 50 of approximately 0.5 mM. Most importantly, the kinetics of receptor activation, determined as 10-90% rise-times, were comparable to synaptic events and were little affected by DPNI-GABA present at 1 mM concentration, permitting photolysis of DPNI-GABA to mimic synaptic activation of GABA A receptors. With a laser spot of 1 m applied to cerebellar molecular layer interneurons, the spatial resolution of uncaging DPNI-GABA in dendrites was estimated as 2 m laterally and 7.5 m focally. Finally, at low DPNI-GABA concentration, photorelease restricted to the area of the soma suppressed spiking in single Purkinje neurons or molecular layer interneurons for periods controlled by the flash intensity and duration. DPNI-GABA has properties better adapted for fast kinetic studies with laser photolysis at GABA A receptors than previously reported caged GABA reagents, and can be used in experiments where spatial resolution is determined by the dimensions of the laser light spot.

The “feathered” cells of Fañanas (FCs) are cerebellar glia of unknown function. Initially described more than a century ago, they have been practically absent from the scientific literature. Here, we combined whole-cell patch-clamp recordings, dye loading and near UV-laser photolysis for a first characterization of FCs in terms of their morphology, electrophysiological properties and glutamate-evoked currents. FCs were identified in cerebellar slices by their small cell bodies located in the molecular layer and stubby processes. Despite a more compact shape compared to Bergmann glia (BGs) FCs had similar membrane resistances and basal currents, suggesting electrical coupling between neighboring glia. Dye filling and pharmacological experiments confirmed homo- and heterotypic gap junction coupling among FCs and BGs. Parallel-fiber stimulation evoked in FCs a slow inward current partially blocked by NBQX, along with superimposed fast (ms) transients. Repetitive stimulations resulted i...

Analog signaling describes the use of graded voltage changes as signals in the axonal compartment. Analog signaling has been described originally in invertebrates but more recent work has established its presence in the mammalian brain . In recent years, many different groups have contributed to the understanding of the physiological significance of analog signaling from a cellular perspective (for a recent review the reader may take a look at the work by Zbili and Debanne, 2019 in this Frontiers in Neuroscience Special Issue). The great majority of the experimental work related to analog signaling, however, concerns the propagation of subthreshold voltage changes from the soma to the axon. Much less attention has been paid to the propagation of subthreshold voltage changes in the opposite direction, from the axon to the soma, or to the propagation of local signals within the axon. In this mini review we will describe these other variants of analog signaling that we call here "antidromic" coupling and "local" coupling.

GABA receptors have been described in the axonal compartment of neurons; contrary to dendritic GABA receptors, axonal GABA receptors usually induce depolarizing responses. In this study we describe the presence of functional axonal GABA receptors in cerebellar Purkinje cells by using a combination of direct patch-clamp recordings from the axon terminals and laser GABA photolysis. In Purkinje cells, axonal GABA receptors are depolarizing and induce an increase in neurotransmitter release that results in a change of short-term synaptic plasticity. These results contribute to our understanding of the cellular mechanisms of action of axonal GABA receptors and highlight the importance of the presynaptic compartment in neuronal computation. In neurons of the adult brain, somatodendritic GABA receptors (GABA Rs) mediate fast synaptic inhibition and play a crucial role in synaptic integration. GABA Rs are not only present in the somatodendritic compartment, but also in the axonal compartmen...

Axonal ionotropic receptors are present in a variety of neuronal types, and their function has largely been associated with the modulation of axonal activity and synaptic release. It is usually assumed that activation of axonal GABAARs comes from spillover, but in cerebellar molecular layer interneurons (MLIs) the GABA source is different: in these cells, GABA release activates presynaptic GABAA autoreceptors (autoRs) together with postsynaptic targets, producing an autoR-mediated synaptic event. The frequency of presynaptic, autoR-mediated miniature currents is twice that of their somatodendritic counterparts, suggesting that autoR-mediated responses have an important effect on interneuron activity. Here, we used local Ca(2+) photolysis in MLI axons of juvenile rats to evoke GABA release from individual varicosities to study the activation of axonal autoRs in single release sites. Our data show that single-site autoR conductances are similar to postsynaptic dendritic conductances. ...

The functional role of synaptic docking sites has remained unclear. Pulido et al. demonstrate that variations in docking site number underlies differences among single GABAergic synapses and that docking site occupancy is modulated during synaptic depression and following depolarizing prepulses.

In cortical and hippocampal neurons, tonic somatic depolarization is partially transmitted to synaptic terminals, where it enhances transmitter release. It is not known to what extent such “analog signaling” applies to other mammalian neurons, and available evidence concerning underlying mechanisms is fragmentary and partially controversial. In this work, we investigate the presence of analog signaling in molecular layer interneurons of the rat cerebellum. GABA release was estimated by measuring autoreceptor currents in single recordings, or postsynaptic currents in paired recordings of synaptically connected neurons. We find with both assays that moderate subthreshold somatic depolarization results in enhanced GABA release. In addition, changes in the calcium concentration were investigated in the axon compartment using the calcium-sensitive dye OGB-1 (Oregon Green BAPTA-1). After a step somatic depolarization, the axonal calcium concentration and the GABA release probability rise ...

Recent evidence indicates the presence of presynaptic GABAAreceptors (GABAARs) in the axon domain of several classes of central neurons, including cerebellar basket and stellate cells. Here, we investigate the possibility that these receptors could be activated in the absence of electrical or chemical stimulation. We find that low concentrations of GABA increase the frequency of miniature GABAergic synaptic currents. Submaximal concentrations of a GABAAR blocker, gabazine, decrease both the miniature current frequency and the probability of evoked GABA release. Zolpidem, an agonist of the benzodiazepine binding site, and NO-711 (1-[2-[[(diphenylmethylene)imino]oxy]ethyl]-1,2,5,6-tetrahydro-3-pyridinecarboxylic acid hydrochloride), a blocker of GABA uptake, both increase the frequency of miniature currents. These effects occur up to postnatal day 14, but not later. Immunohistochemistry indicates the presence of α1-containing GABAARs in interneuron presynaptic terminals with a similar...

To distinguish between different models of vesicular release in brain synapses, it is necessary to know the number of vesicles of transmitter that can be released immediately at individual synapses by a high-calcium stimulus, the readily releasable pool (RRP). We used direct stimulation by calcium uncaging at identified, single-site inhibitory synapses to investigate the statistics of vesicular release and the size of the RRP. Vesicular release, detected as quantal responses in the postsynaptic neuron, showed an unexpected stochastic variation in the number of quanta from stimulus to stimulus at high intracellular calcium, with a mean of 1.9 per stimulus and a maximum of three or four. The results provide direct measurement of the RRP at single synaptic sites. They are consistent with models in which release proceeds from a small number of vesicle docking sites with an average occupancy around 0.7.

Miniature synaptic currents have long been known to represent random transmitter release under resting conditions, but much remains to be learned about their nature and function in central synapses. In this work, we describe a new class of miniature currents (''preminis'') that arise by the autocrine activation of axonal receptors following random vesicular release. Preminis are prominent in gabaergic synapses made by cerebellar interneurons during the development of the molecular layer. Unlike ordinary miniature postsynaptic currents in the same cells, premini frequencies are strongly enhanced by subthreshold depolarization, suggesting that the membrane depolarization they produce belongs to a feedback loop regulating neurotransmitter release. Thus, preminis could guide the formation of the interneuron network by enhancing neurotransmitter release at recently formed synaptic contacts.

Laser photolysis to release GABA at precisely defined times and locations permits investigation of the distribution of functional GABA A receptors in neuronal compartments, the activation kinetics and pharmacology of GABA A receptors in situ, and the role of individual neurons in neural circuits by selective silencing with low GABA concentrations. We describe the experimental evaluation and applications of a new nitroindoline-caged GABA, DPNI-GABA, modified to minimize the pharmacological interference commonly found with caged GABA reagents, but retaining the advantages of nitroindoline cages. Unlike the 5-methoxycarbonylmethyl-7-nitroindolinyl-GABA tested previously, DPNI-GABA inhibited GABA A receptors with much lower affinity, reducing peak GABA-evoked responses with an IC 50 of approximately 0.5 mM. Most importantly, the kinetics of receptor activation, determined as 10-90% rise-times, were comparable to synaptic events and were little affected by DPNI-GABA present at 1 mM concentration, permitting photolysis of DPNI-GABA to mimic synaptic activation of GABA A receptors. With a laser spot of 1 m applied to cerebellar molecular layer interneurons, the spatial resolution of uncaging DPNI-GABA in dendrites was estimated as 2 m laterally and 7.5 m focally. Finally, at low DPNI-GABA concentration, photorelease restricted to the area of the soma suppressed spiking in single Purkinje neurons or molecular layer interneurons for periods controlled by the flash intensity and duration. DPNI-GABA has properties better adapted for fast kinetic studies with laser photolysis at GABA A receptors than previously reported caged GABA reagents, and can be used in experiments where spatial resolution is determined by the dimensions of the laser light spot.

Axons are equipped with the digital signaling capacity by which they generate and faithfully propagate action potentials (APs), and also with the analogue signaling capacity by which subthreshold activity in dendrites and soma is transmitted down the axon. Despite intense work, the extent and physiological role for subthreshold synaptic activity reaching the axonal boutons has remained elusive because of the technical limitation to record from them. To address this issue, we made simultaneous patch-clamp recordings from the axonal varicosities of cerebellar GABAergic interneurons together with their parent soma or postsynaptic target cells in young rat slices and/or primary cultures. Ourtour-de-forcedirect functional dissection indicates that the somatodendritic spontaneous EPSPs are transmitted down the axon for significant distances, depolarizing presynaptic boutons. These analogously transmitted EPSPs augment presynaptic Ca++influx upon arrival of an immediately following AP thro...

Modification of GABAergic inhibition is an intensely investigated hypothesis guiding research into mechanisms underlying temporal lobe epilepsy (TLE). Seizures can be initiated by blocking γ amino butyric acid type A (GABA A receptors, GABARs), which mediate fast synaptic inhibition in the brain, and controlled by drugs that enhance their function. Derivatives of steroid hormones called neurosteroids are natural substances that physiologically enhance GABAR function and suppress seizures. GABAR structure, function, expression, assembly, and pharmacological properties are changed in the hippocampus of epileptic animals. These alterations render GABARs less sensitive to neurosteroid modulation, which may contribute to seizure susceptibility. Plasticity of GABARs could play a role in periodic exacerbation of seizures experienced by women with epilepsy, commonly referred to as catamenial epilepsy.

The critical, fundamental mechanisms that determine the emergence of status epilepticus from a single seizure and the prolonged duration of status epilepticus are uncertain. However, several general concepts of the pathophysiology of status epilepticus have emerged: (a) the hippocampus is consistently activated during status epilepticus; (b) loss of GABAmediated inhibitory synaptic transmission in the hippocampus is critical for emergence of status epilepticus; and, finally (c) glutamatergic excitatory synaptic transmission is important in sustaining status epilepticus. This review focuses on the alteration of GABAergic inhibition in the hippocampus that occurs during the prolonged seizures of status epilepticus. If reduction in GABAergic inhibition leads to development of status epilepticus, enhancement of GABAergic inhibition would be expected to interrupt status epilepticus. Benzodiazepines and barbiturates are both used in the treatment of status epilepticus and both drugs enhance GABA, receptor-mediated inhibition. However, patients often become refractory to benzodiazepines when seizures are prolonged, and barbiturates are often then used for these refractory cases of status epilepticus. Recent evidence suggests the presence of multiple GABA, receptor isoforms in the hippocampus with different sensitivity to benzodiazepines but similar sensitivity to barbiturates, thus ex-~~~ ~

Rats were kindled with either of 2 protocols: (1) a rapidly recurring hippocampal seizure (RRHS) paradigm in which 10 set stimulus trains were delivered every 5 min through hippocampal electrodes; and (2) a traditional approach in which 1 set stimulus trains were given to the amygdala once daily. Three groups of kindled rats were prepared: (1) one of amygdala-kindled rats that had experienced 9-15 seizures; (2) one of RRHS-kindled rats that had experienced 96 seizures; and (3) one of RRHS-overkindled rats that had experienced 144-336 seizures. After a 1 month seizure-free period, the animals were anesthetized with urethane and measurements were made on the potency of paired pulse inhibition in the CA1 region of the hippocampus. All groups of kindled animals were found to have significantly less paired pulse inhibition than control rats. This decrement was confined to interpulse intervals s70 msec. The amount of inhibition lost correlated with the number of seizure that had occurred. The GABAergic agonist muscimol restored paired pulse inhibition in kindled animals for interpulse intervals <70 msec towards normal values. These results indicate that not only RRHS, but also other modes of kindling, reduced GABAergic inhibition in the CA1 region of the hippocampus and that this diminution was long-lasting, if not permanent.