Increase In Neuronal Activity Research Articles

Enhancing excitatory projections from the ventral subiculum to the nucleus accumbens shell contribute to the MK-801-induced impairment of prepulse inhibition

Prepulse inhibition (PPI), a measure of sensorimotor gating, has been shown to be disrupted in several animal models of neuropsychiatric disorders, such as schizophrenia. The neural circuits involving the hippocampus and nucleus accumbens (NAC) have been studied in rats to uncover the neurochemical and neuroanatomical substrates that regulate PPI. Majority of the studies of the hippocampus on PPI to date have been focused on CA1, CA2, and dentate gyrus (DG) area. Little is known about the role of the subiculum, which maintains the hippocampal formation intact, on the sensorimotor gating. In this study, the PPI disruption was induced by intraperitoneal injection of MK-801 in rats, and the neuronal activity in the dorsal and ventral subiculum by c-Fos immunostaining was examined. The projections from the subiculum to the nucleus accumbens (NAC) were detected by retrograde tracing of cholera toxin B subunit, in the PPI dysfunctional animals. The results showed an increase in neuronal activity in the ventral subiculum (vSub) while remaining constant in the dorsal subiculum during PPI disruption. The excitatory projections from the vSub to the NAC shell were significantly enhanced when PPI was disrupted. Muscimol Inhibition of vSub could significantly ameliorate the MK801-induced PPI deficit. This data suggests that the enhancement of neuronal activity in the vSub was associated with the PPI impairment, possibly due to the enhanced excitatory output from vSub the NAC shell.

Gastric Distension‐induced Nodose Ganglionic Cell Responses Using a High‐throughput Multi‐electrode Array in the Ferret

The nodose ganglion (NG) contains cell bodies of gastrointestinal afferents, which play critical roles in metabolic and feeding disorders and gastrointestinal and inflammatory diseases. To further understand the population coding of nodose ganglionic signals, we used a 32‐chan multi‐electrode array (MEA; 4×8, 400 μm pitch; Blackrock Microsystems) to record single‐unit responses with 3 main objectives: (1) determine the stability of multiple single‐unit responses during several hours of in vivo electrophysiological recording; (2) measure the activation patterns of these neurons to prototypical stimulation, such as gastric distension; and (3) investigate the phenotypes of nodose neurons using mechanical probing and vagus nerve electrical stimulation to determine conduction velocities. Acute experiments were performed in anesthetized ferrets using inhalational isoflurane (~2.5%) anesthesia. MEAs were inserted in the nodose ganglion using a pneumatic inserter, and a balloon‐catheter was advanced into the stomach through a small incision on the lateral edge of the gastric fundus. Two volumes of saline, 10 and 20 ml, were infused into the balloon to provide distension. Nerve cuff electrodes were placed on the abdominal vagus trunk to determine conduction velocity. Ganglionic single‐unit activity was successfully recorded from the NG for up to 5.3 h. In our preliminary analysis using spike sorting on each channel (MKsort, https://github.com/ripple‐neuro/mksort; Matlab), we were able to identify a total of 233 units in 6 animals (16 to 55 units per animal). Gastric balloon distension produced >20% increase in neuronal activity in an average of 48% of units to 10 ml inflation and 56% of units to 20 ml inflation. These results demonstrate the feasibility to record multiple single‐unit responses from the ferret NG to provide insight into gastric‐related population coding. Future effort could focus on delineating the physiological roles of these gastric neurons for the design of neuromodulation devices, which could be used to treat diseases involving vagal sensory input such as obesity and the chronic nausea associated with gastroparesis.Support or Funding InformationThis research was supported by funding from the NIH SPARC Common Fund Program (award #U18TR002205).

Reduced neurosteroid potentiation of GABAA receptors in epilepsy and depolarized hippocampal neurons.

ObjectiveNeurosteroids regulate neuronal excitability by potentiating γ‐aminobutyric acid type‐A receptors (GABARs). In animal models of temporal lobe epilepsy, the neurosteroid sensitivity of GABARs is diminished and GABAR subunit composition is altered. We tested whether similar changes occur in patients with epilepsy and if depolarization‐induced increases in neuronal activity can replicate this effect.MethodsWe determined GABAR α4 subunit expression in cortical tissue resected from pediatric epilepsy patients. Modulation of human GABARs by allopregnanolone and Ro15‐4513 was measured in Xenopus oocytes using whole‐cell patch clamp. To extend the findings obtained using tissue from epilepsy patients, we evaluated GABAR expression and modulation by allopregnanolone and Ro15‐4513 in cultured rat hippocampal neurons exposed to high extracellular potassium (HK) to increase neuronal activity.ResultsExpression of α4 subunits was increased in pediatric cortical epilepsy specimens encompassing multiple pathologies. The potentiation of GABA‐evoked currents by the neurosteroid allopregnanolone was decreased in Xenopus oocytes expressing GABARs isolated from epilepsy patients. Furthermore, receptors isolated from epilepsy but not control tissue were sensitive to potentiation by Ro15‐4513, indicating higher expression of α 4 β x γ 2 subunit‐containing receptors. Correspondingly, increasing the activity of cultured rat hippocampal neurons reduced allopregnanolone potentiation of miniature inhibitory postsynaptic currents (mIPSCs), increased modulation of tonic GABAR current by Ro15‐4513, upregulated the surface expression of α4 and γ2 subunits, and increased the colocalization of α4 and γ2 subunit immunoreactivity.InterpretationThese findings suggest that seizure activity‐induced upregulation of α 4 β x γ 2 subunit‐containing GABARs could affect the anticonvulsant actions of neurosteroids.

Novel Control Mechanism of the Neurovascular Coupling in an Alzheimer’s Disease Model

Alzheimer’s disease (AD) is a type of dementia related to age characterized by a progressive and irreversible deterioration of memory and general cognitive abilities. There is a consensus that the production of β‐amyloid protein (Aβ) aggregates correlates with neuronal alterations, triggering the characteristic neurodegeneration process of this disease. Furthermore, disease progression has been closely associated with cerebral vascular alterations, such as reduction in cerebral blood flow observed in patients and animal models of AD.It has been documented that Aβ not only has harmful effects at neuronal level but has also been associated with the alteration of astrocytes normal activity. One of the events modulated by astrocytes at cerebral level is its key role in the neurovascular coupling (NVC), mechanism that ensures nutrients and oxygen supply in proportion to the increase in neuronal activity. The NVC functions controlled by the astrocytes is mediated by vasodilator signals, a process that is dependent of intracellular calcium increase in astrocytes, which is propagated and coordinated by the release of paracrine and autocrine adenosine triphosphate (ATP).There is no consensus about the way of ATP release from astrocytes during NVC, but the description of a new channel, Calcium Homeostasis Modulator 1 (CALHM1) which permit the ATP release in some type of neurons, could be an important element in astrocyte signaling during this mechanism. In previous results we observed that ATP is released through CALHM1 in an astrocyte primary culture model stimulated with glutamate (a stimulus validated in NVC studies) and also was dependent of the CALHM1 activation by S‐nitrosylation through nitric oxide (NO) produced by the astrocytes.Considering that it has been reported that NVC is altered in AD, which contribute to the pathophysiological mechanisms of this disease, our main aim was to evaluate the ATP release in astrocytes primary cultures from a validated murine model of AD: B6C3‐Tg(APPswe,PSEN1dE9)85Dbo/Mmjax.Our results show that ATP release, and CALHM1 relative levels and expression are significatively reduced in astrocytes primary cultures from AD animals in comparing with cultures from wild type animals. These results suggest that calcium signaling could be diminished in the astrocytes in AD and could explicate the relation between the alteration of NVC in AD.Support or Funding InformationUniversidad del Desarrollo Intern Proyect 23.400.163

Direct Medial Entorhinal Cortex Input to Hippocampal CA3 Is Crucial for eEF2K Inhibitor-Induced Neuronal Oscillations in the Mouse Hippocampus.

The hippocampal formation plays a vital role in memory formation and takes part in the control of the default neuronal network activity of the brain. It also represents an important structure to analyze drug-induced effects on subregion-specific synchronization of neuronal activity. However, the consequences of an altered functional state of synapses for subregion-specific synchronization of neuronal microcircuits remain to be fully understood. Therefore, we analyzed the direct interaction of neuronal microcircuits utilizing a genetically encoded calcium sensor (GCaMP6s) and local field potential (LFP) recording in acute hippocampal–entorhinal brain slices in response to a modulator of synaptic transmission. We observed that application of the eukaryotic elongation factor-2 kinase (eEF2K) inhibitor A484954, induced a large-scale synchronization of neuronal activity within different regions of the hippocampal formation. This effect was confirmed by the recording of extracellular LFPs. Further, in order to understand if the synchronized activity depended on interconnected hippocampal areas, we lesioned adjacent regions from each other. These experiments identified the origin of A484954-induced synchronized activity in the hippocampal CA3 subfield localized near the hilus of the dentate gyrus. Remarkably, the synchronization of neuronal activity in the hippocampus required an intact connection with the medial entorhinal cortex (MEC). In line with this observation, we detected an increase in neuronal activity in the MEC area after application of A484954. In summary, inhibition of eEF2K alters the intrinsic activity of interconnected neuronal microcircuits dominated by the MEC–CA3 afferents.

PIK3CA variants selectively initiate brain hyperactivity during gliomagenesis.

Glioblastoma is a universally lethal form of brain cancer that exhibits an array of pathophysiological phenotypes, many of which are mediated by interactions with the neuronal microenvironment1,2. Recent studies have shown that increases in neuronal activity have an important role in the proliferation and progression of glioblastoma3,4. Whether there is reciprocal crosstalk between glioblastoma and neurons remains poorly defined, as the mechanisms that underlie how these tumours remodel the neuronal milieu towards increased activity are unknown. Here, using a native mouse model of glioblastoma, we develop a high-throughput in vivo screening platform and discover several driver variants of PIK3CA. We show that tumours driven by these variants have divergent molecular properties that manifest in selective initiation of brain hyperexcitability and remodelling of the synaptic constituency. Furthermore, secreted members of the glypican (GPC) family are selectively expressed in these tumours, and GPC3 drives gliomagenesis and hyperexcitability. Together, our studies illustrate the importance of functionally interrogating diverse tumour phenotypes driven by individual, yet related, variants and reveal how glioblastoma alters the neuronal microenvironment.

Lévy noise-induced near-death spikes and phase transitions of a biological neural network

Near-death spikes or near-death surges are a sudden increase in neuron activity in the human brain before neurons end their firings. Just before a person is clinically dead, such spikes are observed in certain cases, so the name is near-death spikes. The reason for this behavior is the lack of oxygen in brain (Chawla et al. in J Palliat Med 12(12):1095–1100, 2009). In this study, it is demonstrated that a particular type of noise called Levy noise can generate such activity in the neural network of the worm Caenorhabditis elegans. The study identified different parameter regions of noise at which the network makes transitions from one synchronous state to another and the mechanism behind them. Such transitions are already reported in cortical regions of brain (Canavero et al. in Surg Neurol Int 7(Suppl 24):S623–S625, 2016). During the transition period between asynchronous and synchronous firing states, network is more susceptible to changes in firing pattern of individual neurons (Zandt et al. in PLoS ONE 6(7):e22127, 2011; Uzuntarla et al. Neural Netw 110:131–140, 2019). In this work, it is demonstrated that the recognized parameter regions can be used to control the network dynamics. The study also identified Levy noise values at which the network displays generation of waves of different frequencies. This result suggests a new method for neurostimulation in the case of traumatic brain injury. The study reveals that the characteristic exponent ($$\alpha $$) of the noise has better influence on the network dynamics than the scale parameter of noise (D) and the synaptic coupling constant (Gsyn) of the network. The neuronal network even displayed Gamma oscillations for large values of $$\alpha $$. If the parameters of the neurons are made chaotic, the network firing rate is diminished and it displayed Delta and Theta oscillations.

Neural mechanisms underlying stress-induced enhancement of cocaine craving behaviors

Stress potentiates craving for addictive drugs including cocaine. To elucidate neural mechanisms underlying this effect of stress, we developed an experimental paradigm combining cocaine-induced conditioned place preference (CPP) with a restraint stress. Acute restraint stress exposure immediately before posttest significantly increased cocaine CPP scores. It has been suggested that the extracellular noradrenaline (NA) level is increased by stress in the laterodorsal tegmental nucleus (LDT), which sends cholinergic projections to dopamine (DA) neurons in the ventral tegmental area (VTA), and medial prefrontal cortex (mPFC), which receives DA input from the VTA. Thus, we investigated the roles of NA in these brain regions. Intra-LDT injection of an α2 or a β adrenoceptor antagonist attenuated the stress-induced enhancement of cocaine CPP. In vitro whole-cell recordings revealed that α2 adrenoceptor stimulation reduced GABAergic inputs to LDT cholinergic neurons that were obtained from cocaine-, but not saline-, treated rats. On the other hand, α1, but not α2 or β, adrenoceptor stimulation excited mPFC pyramidal neurons. Intra-mPFC injection of an α1 adrenoceptor antagonist attenuated the stress-induced enhancement of cocaine CPP. Additionally, chemogenetic silencing of mPFC excitatory neurons also reduced the stress-induced enhancement of cocaine CPP. These findings suggest that stress-induced increases in neuronal activity of the LDT and mPFC may contribute to the enhancement of cocaine craving.

Cocaine and chronic stress exposure produce an additive increase in neuronal activity in the basolateral amygdala

Cocaine addiction is a chronic, relapsing disorder. Stress and cues related to cocaine are two common relapse triggers. We have recently shown that exposure to repeated restraint stress during early withdrawal accelerates the time-dependent intensification or "incubation" of cue-induced cocaine craving that occurs during the first month of withdrawal, although craving ultimately plateaus at the same level observed in controls. These data indicate that chronic stress exposure during early withdrawal may result in increased vulnerability to cue-induced relapse during this period. Previous studies have shown that chronic stress exposure in drug-naïve rats increases neuronal activity in the basolateral amygdala (BLA), a region critical for behavioral responses to stress. Given that glutamatergic projections from the BLA to the nucleus accumbens are critical for the incubation of cue-induced cocaine craving, we hypothesized that cocaine withdrawal and chronic stress exposure produce separate increases that additively increase BLA neuronal activity. To assess this, we conducted in vivo extracellular single-unit recordings from the BLA of anesthetized adult male rats following cocaine or saline self-administration (6 h/day for 10 days) and repeated restraint stress or control conditions on withdrawal days (WD) 6-14. Recordings were conducted from WD15 to WD20. Interestingly, cocaine exposure alone increased the spontaneous firing rate in the BLA to levels observed following chronic stress exposure in drug-naïve rats. Chronic stress exposure during cocaine withdrawal further increased firing rate. These studies may identify a potential mechanism by which both cocaine and chronic stress exposure drive cue-induced relapse vulnerability during abstinence.

Hearing impairment and associated morphological changes in pituitary adenylate cyclase activating polypeptide (PACAP)-deficient mice

Pituitary adenylate cyclase activating polypeptide (PACAP) is a regulatory and cytoprotective neuropeptide, its deficiency implies accelerated aging in mice. It is present in the auditory system having antiapoptotic effects. Expression of Ca2+-binding proteins and its PAC1 receptor differs in the inner ear of PACAP-deficient (KO) and wild-type (WT) mice. Our aim was to elucidate the functional role of PACAP in the auditory system. Auditory brainstem response (ABR) tests found higher hearing thresholds in KO mice at click and low frequency burst stimuli. Hearing impairment at higher frequencies showed as reduced ABR wave amplitudes and latencies in KO animals. Increase in neuronal activity, demonstrated by c-Fos immunolabeling, was lower in KO mice after noise exposure in the ventral and dorsal cochlear nuclei. Noise induced neuronal activation was similar in further relay nuclei of the auditory pathway of WT and KO mice. Based on the similar inflammatory and angiogenic protein profile data from cochlear duct lysates, neither inflammation nor disturbed angiogenesis, as potential pathological components in sensorineural hearing losses, seem to be involved in the pathomechanism of the presented functional and morphological changes in PACAP KO mice. The hearing impairment is probably concomitant with the markedly accelerated aging processes in these animals.

Pathogenic Tau Impairs Axon Initial Segment Plasticity and Excitability Homeostasis

Dysregulation of neuronal excitability underlies the pathogenesis of tauopathies, including frontotemporal dementia (FTD) with tau inclusions. A majority of FTD-causing tau mutations are located in the microtubule-binding domain, but how these mutations alter neuronal excitability is largely unknown. Here, using CRISPR/Cas9-based gene editing in human pluripotent stem cell (iPSC)-derived neurons and isogenic controls, we show that the FTD-causing V337M tau mutation impairs activity-dependent plasticity of the cytoskeleton in the axon initial segment (AIS). Extracellular recordings by multi-electrode arrays (MEAs) revealed that the V337M tau mutation in human neurons leads to an abnormal increase in neuronal activity in response to chronic depolarization. Stochastic optical reconstruction microscopy of human neurons with this mutation showed that AIS plasticity is impaired by the abnormal accumulation of end-binding protein 3 (EB3) in the AIS submembrane region. These findings expand our understanding of how FTD-causing tau mutations dysregulate components of the neuronal cytoskeleton, leading to network dysfunction.

Group 1 metabotropic glutamate receptors trigger glutamate-induced intracellular Ca2+ signals and nitric oxide release in human brain microvascular endothelial cells.

Neurovascular coupling (NVC) is the mechanism whereby an increase in neuronal activity causes an increase in local cerebral blood flow (CBF) to ensure local supply of oxygen and nutrients to the activated areas. The excitatory neurotransmitter glutamate gates post-synaptic N-methyl-D-aspartate receptors to mediate extracellular Ca2+ entry and stimulate neuronal nitric oxide (NO) synthase to release NO, thereby triggering NVC. Recent work suggested that endothelial Ca2+ signals could underpin NVC by recruiting the endothelial NO synthase. For instance, acetylcholine induced intracellular Ca2+ signals followed by NO release by activating muscarinic 5 receptors in hCMEC/D3 cells, a widely employed model of human brain microvascular endothelial cells. Herein, we sought to assess whether also glutamate elicits metabotropic Ca2+ signals and NO release in hCMEC/D3 cells. Glutamate induced a dose-dependent increase in intracellular Ca2+ concentration ([Ca2+]i) that was blocked by α-methyl-4-carboxyphenylglycine and phenocopied by trans-1-amino-1,3-cyclopentanedicarboxylic acid, which, respectively, block and activate group 1 metabotropic glutamate receptors (mGluRs). Accordingly, hCMEC/D3 expressed both mGluR1 and mGluR5 and the Ca2+ response to glutamate was inhibited by their pharmacological blockade with, respectively, CPCCOEt and MTEP hydrochloride. The Ca2+ response to glutamate was initiated by endogenous Ca2+ release from the endoplasmic reticulum and endolysosomal Ca2+ store through inositol-1,4,5-trisphosphate receptors and two-pore channels, respectively, and sustained by store-operated Ca2+ entry. In addition, glutamate induced robust NO release that was suppressed by pharmacological blockade of the accompanying increase in [Ca2+]i. These data demonstrate for the first time that glutamate may induce metabotropic Ca2+ signals in human brain microvascular endothelial cells. The Ca2+ response to glutamate is likely to support NVC during neuronal activity, thereby reinforcing the emerging role of brain microvascular endothelial cells in the regulation of CBF.

A Major Role for the Lateral Habenula in Depressive Illness: Physiologic and Molecular Mechanisms.

Emerging preclinical and clinical evidence indicate that the lateral habenula plays a major role in the pathophysiology of depressive illness. Aberrant increases in neuronal activity in the lateral habenula, an anti-reward center, signals down-regulation of brainstem dopaminergic and serotonergic firing, leading to anhedonia, helplessness, excessive focus on negative experiences, and, hence, depressive symptomatology. The lateral habenula has distinctive regulatory adaptive role to stress regulation in part due to its bidirectional connectivity with the hypothalamic–pituitary–adrenal (HPA) axis. In addition, studies show that increased lateral habenula activity affects components of sleep regulation including slow wave activity and rapid eye movement (REM), both disrupted in depressive illness. Lack of perceived reward experienced during the adverse outcomes also precipitates lateral habenula firing, while outcomes that meet or exceed expectations decrease lateral habenula firing and, in turn, increase midbrain dopaminergic and serotonergic neurotransmission. The ability to update expectations of the environment based on rewards and aversive stimuli reflects a potentially important survival mechanism relevant to the capacity to adapt to changing circumstances. What if one lives in a continuously aversive and invalidating environment or under the conditions of chronic stress? If there is a propensity of the habenula to release many burst discharges over time, an individual could habitually come to perceive the world as perpetually disappointing. Conceivably, the lateral habenula could learn to expect an adverse outcome systematically and communicate it more easily. Thus, if the lateral habenula fires more frequently, it may lead to a state of continuous disappointment and hopelessness, akin to depression. Furthermore, postmortem studies reveal that the size of the lateral habenula and total number of neurons are decreased in patients who had depressive illness. Novel research in the field shows that ketamine induces rapid and sustained antidepressant effect. Intriguingly, recent preclinical animal models show that ketamine abolishes N-methyl-D-aspartate receptor (NMDAR)-dependent lateral habenula bursting activity, leading to rapid resolution of depressive symptoms.

Inhibition of T-Type calcium channels in mEC layer II stellate neurons reduces neuronal hyperexcitability associated with epilepsy

Temporal lobe epilepsy (TLE) is a form of adult epilepsy involving the entorhinal cortex (EC). Layer II neurons of the medial EC (mEC) are spared and become hyperexcitable in TLE. Studies have suggested a role for T-type calcium channels (T-type Ca2+ channels) in facilitating increases in neuronal activity associated with TLE within the hippocampus. We sought to determine if T-type Ca2+ channels play a role in facilitating neuronal hyperexcitability of layer II mEC stellate neurons in TLE.TLE was induced in rats by electrical stimulation of the hippocampus to induce status epilepticus (SE). Brain slices were prepared from rats exhibiting spontaneous seizures and compared with age-matched control rats. Action potentials (APs) were evoked either by current injection steps or via presynaptic stimulation of mEC deep layers. The selective T-type Ca2+ channel antagonist, TTA-P2 (1 μM), was applied to determine the role of T-type Ca2+ channels in maintaining neuronal excitability. Quantitative PCR techniques were used to assess T-type Ca2+ channel isoform mRNA levels within the mEC layer II.TLE mEC layer II stellate neurons were hyperexcitable compared to control neurons, evoking a higher frequency of APs and generating bursts of APs when synaptically stimulated. TTA-P2 (1 μM) reduced firing frequencies in TLE and control neurons and reduced AP burst firing in TLE stellate neurons. TTA-P2 had little effect on synaptically evoked AP’s in control neurons. TTA-P2 also inhibited rebound APs evoked in TLE neurons to a greater degree than in control neurons. TLE tissue had almost a 3-fold increase in Cav3.1 mRNA compared to controls. Cav3.2 or Cav3.3 levels were unchanged.These findings support a role for T-type Ca2+ channel in establishing neuronal hyperexcitability of mEC layer II stellate neurons in TLE. Increased expression of Cav3.1 may be important for establishing neuronal hyperexcitability of mEC layer II neurons in TLE.

Probiotic treatment restores normal developmental trajectories of fear memory retention in maternally separated infant rats

Early life stress (ELS) can affect brain development and increase lifetime prevalence of psychiatric illnesses. However, the effective therapeutic interventions to ameliorate the deleterious effects of ELS have not yet been well established. Here, we confirmed that maternal separation (MS) for 3 h daily between postnatal days 2–14, a frequently used experimental model of ELS, resulted in early expression of adult-like fear memory retention in male infant rats. Administration of a probiotic formulation, Lacidofil® (95% Lactobacillus rhamnosus R0011 and 5% Lactobacillus helveticus R0052), during the separation period, prevented the precocious transition to adult-like fear memory retention in MS infant rats. Consonant with this effect, probiotic treatment also ameliorated the MS-induced increases in anxiety-like behavior as measured by the elevated plus maze and the light-dark box tests. In addition, probiotic treatment reduced MS-induced increases in neuronal activation and brain-derived neurotrophic factor protein levels in the basolateral nucleus of amygdala (BLA) after auditory fear conditioning. Furthermore, we found that probiotic treatment significantly rescued the heightened hypothalamic-pituitary-adrenal (HPA) axis response to restraint stress in MS infant rats. Taken together, these findings suggest that probiotics can restore normal developmental trajectories of fear memory retention in MS infant rats, at least in part by normalizing HPA axis abnormalities, and that the BLA serves as a critical node to mediate these interventions. Thus, we offer a potential therapeutic intervention to protect children against the harmful effects of ELS.

Electrophysiological approach to the hypothalamic GnRH pulse generator

The hypothalamic GnRH pulse generator that regulates intermittent GnRH discharge into the pituitary portal circulation and thereby modulates pulsatile secretion of LH has been recognized as a key determinant of the reproductive function in mammals. Thus, various internal, as well as external, factors first modify the electrical activity of the GnRH pulse generator, which then alters the pulsatile pattern of gonadotrophin secretion and eventually influences reproductive function. Here, we describe a procedure that has permitted long-term recording of electrophysiological manifestation of the GnRH pulse generator activity and its application to our research which uses ovariectomized and cyclic female goats as experimental models. We have successfully recorded characteristic increases in neuronal activity associated with pulsatile LH secretion from conscious goats by means of a multiple unit activity (MUA) recording technique, which is an adaptation of that developed originally for use in rhesus monkeys. The unitary relationship between periodical increases in MUA (MUA volleys) and LH pulses is well maintained under a variety of experimental conditions, providing evidence that these MUA volleys are the consequence of GnRH pulse generator activity.

Chronic pain after blast-induced traumatic brain injury in awake rats

Explosive blast-induced traumatic brain injury (blast-TBI) in military personnel is a leading cause of injury and persistent neurological abnormalities, including chronic pain. We previously demonstrated that chronic pain after spinal cord injury results from central sensitization in the posterior thalamus (PO). The presence of persistent headaches and back pain in veterans with blast-TBI suggests a similar involvement of thalamic sensitization. Here, we tested the hypothesis that pain after blast-TBI is associated with abnormal increases in activity of neurons in PO thalamus. We developed a novel model with two unique features: (1) blast-TBI was performed in awake, un-anesthetized rats, to simulate the human experience and to eliminate confounds of anesthesia and surgery inherent in other models; (2) only the cranium, rather than the entire body, was exposed to a collimated blast wave, with the blast wave striking the posterior cranium in the region of the occipital crest and foramen magnum. Three weeks after blast-TBI, rats developed persistent, ongoing spontaneous pain. Contrary to our hypothesis, we found no significant differences in the activity of PO neurons, or of neurons in the spinal trigeminal nucleus. There were also no significant changes in gliosis in either of these structures. This novel model will allow future studies on the pathophysiology of chronic pain after blast-TBI.

Synchronized activation of striatal direct and indirect pathways underlies the behavior in unilateral dopamine-depleted mice.

For more than three decades it has been known, that striatal neurons become hyperactive after the loss of dopamine input, but the involvement of dopamine (DA) D1‐ or D2‐receptor‐expressing neurons has only been demonstrated indirectly. By recording neuronal activity using fluorescent calcium indicators in D1 or D2 eGFP‐expressing mice, we showed that following dopamine depletion, both types of striatal output neurons are involved in the large increase in neuronal activity generating a characteristic cell assembly of particular neurons that dominate the pattern. When we expressed channelrhodopsin in all the output neurons, light activation in freely moving animals, caused turning like that following dopamine loss. However, if the light stimulation was patterned in pulses the animals circled in the other direction. To explore the neuronal participation during this stimulation we infected normal mice with channelrhodopsin and calcium indicator in striatal output neurons. In slices made from these animals, continuous light stimulation for 15 s induced many cells to be active together and a particular dominant group of neurons, whereas light in patterned pulses activated fewer cells in more variable groups. These results suggest that the simultaneous activity of a large dominant group of striatal output neurons is intimately associated with parkinsonian symptoms.

Lateral epicondylalgia: A primary nervous system disorder

Lateral epicondylalgia (LE) is the most common chronic painful condition affecting the elbow in the general population. Although major advances have been accomplished in recent years in the understanding of LE, the underlying physiopathology is still a reason for debate. Differences in clinical presentation and evolution of the symptoms among patients, suggest the need for revisiting the current knowledge about subjacent mechanisms that attempt to explain pain and functional loss. Previous models have suggested that the condition is mainly a degenerative tendinopathy, associated with changes in pain pathways and the motor system. The hypothesis of this work is that LE is the clinical manifestation of a primary nervous system disorder, characterized by an abnormal increase in neuronal activity and a subsequent loss of homeostasis, which secondarily affects the musculoskeletal tissues of the elbow-forearm-hand complex. A new model for LE is presented, supported by an in-deep analysis of basic sciences, epidemiological and clinical studies.

Targeted knockout of GABA-A receptor gamma 2 subunit provokes transient light-induced reflex seizures in zebrafish larvae.

ABSTRACTEpilepsy is a common primary neurological disorder characterized by the chronic tendency of a patient to experience epileptic seizures, which are abnormal body movements or cognitive states that result from excessive, hypersynchronous brain activity. Epilepsy has been found to have numerous etiologies and, although about two-thirds of epilepsies were classically considered idiopathic, the majority of those are now believed to be of genetic origin. Mutations in genes involved in gamma-aminobutyric acid (GABA)-mediated inhibitory neurotransmission have been associated with a broad range of epilepsy syndromes. Mutations in the GABA-A receptor gamma 2 subunit gene (GABRG2), for example, have been associated with absence epilepsy and febrile seizures in humans. Several rodent models of GABRG2 loss of function depict clinical features of the disease; however, alternative genetic models more amenable for the study of ictogenesis and for high-throughput screening purposes are still needed. In this context, we generated a gabrg2 knockout (KO) zebrafish model (which we called R23X) that displayed light/dark-induced reflex seizures. Through high-resolution in vivo calcium imaging of the brain, we showed that this phenotype is associated with widespread increases in neuronal activity that can be effectively alleviated by the anti-epileptic drug valproic acid. Moreover, these seizures only occur at the larval stages but disappear after 1 week of age. Interestingly, our whole-transcriptome analysis showed that gabrg2 KO does not alter the expression of genes in the larval brain. As a result, the gabrg2−/− zebrafish is a novel in vivo genetic model of early epilepsies that opens new doors to investigate ictogenesis and for further drug-screening assays.