GABA Receptor Expression Research Articles

The effect of intrathecal injection of irisin on pain threshold and expression rate of GABAB receptors in peripheral neuropathic pain model

Backgroundand aim: Irisin is a new myokine that is secreted by myocytes during exercise, and plays a role in creating the beneficial effects of exercise on metabolism. Considering the benefits of exercise in reducing pain, this study was carried out to determine the probable effect of irisin on neuropathic pain in the chronic constriction injury (CCI) model in male rats. MethodsTo induce neuropathic pain CCI model was used. Animals were divided into groups of control, CCI, sham, CCI + vehicle, and CCI + irisin. Animals that had undergone CCI were divided into 6 groups and each received a different intrathecal dose of irisin (30, 10, 3, 1, 0.3, and 0.1 μg/kg) via intrathecal administration. To evaluate the chronic effect of irisin, its effective dose was injected for 14 days in another group of animals. At the end of the experiment, animals were ranscardially perfused and their spinal cord tissue was prepared for immunohistochemical and hematoxylin-eosin staining. ResultsThe results showed that in acute intrathecal injection of irisin, 1 μg/kg dose has the highest analgesic effect compared to other doses. Nevertheless, in chronic administration of irisin with 1 μg/kg dose, no analgesic effect was detected. In addition, irisin administration could not increase the expression level of GABAB1 and B2 or prevent the decline in the number of neurons. ConclusionThe findings of the present study showed that acute administration of Irisin increases the pain threshold, but the chronic injection of resin does not have an effect on pain reduction and the expression of GABA receptors and it seems that this peptide is not a proper replacement for exercise in patients with neuropathic pain, who cannot exercise.

GABAergic System in Action: Connection to Gastrointestinal Stress-related Disorders

Currently, treatment of stress-related gastrointestinal disorders, such as inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS), is mainly symptomatic since there is no drug on the market that solves effectively diverse disease symptoms and comorbid states. Recently GABA receptors have been identified within gastrointestinal system and it has been recognized that among various GABAergic drugs some of them influence gastrointestinal stress-related diseases. Among them benzodiazepines have been investigated due to their diverse effects: neuroimmunomodulatory, relief of visceral pain and anxiolytic action. The present review brings findings on the expression of GABA receptors in the gastrointestinal tract and the role of GABA within it. We also present knowledge on the role of neurotransmitter GABA and various GABAergic ligands on diverse physiologic gastrointestinal functions with special emphasize to stress-related disorders. The rationale for therapeutic use and further identification of a potential GABAergic treatment of stress-related disorders has been critically discussed.

P.4.a.017 - From uncertainty to checking: the role of metacognitive monitoring in obsessive compulsive disorder (OCD)

In addition to important metabolic functions in the brain, GABA is a neurotransmitter of major significance, being released by up to 40% of neurons to activate chloride channels resulting generally in inhibition of neuronal firing. Its ubiquitous presence in the brain and spinal cord means that almost all neurons either release GABA, express GABA receptors, or are innervated by neurons that do. GABA mechanisms are thought to be involved in anesthesia, anxiety, epilepsy, memory, neurodegenerative disorders, schizophrenia, sleep, stress, cardiovascular, and neuroendocrine function. Many agents act through GABA mechanisms including barbiturates, benzodiazepines, ethanol, flavonoids, general anesthetics, and neuroactive steroids.

Testing the excitation/inhibition imbalance hypothesis in a mouse model of the autism spectrum disorder: in vivo neurospectroscopy and molecular evidence for regional phenotypes

BackgroundExcitation/inhibition (E/I) imbalance remains a widely discussed hypothesis in autism spectrum disorders (ASD). The presence of such an imbalance may potentially define a therapeutic target for the treatment of cognitive disabilities related to this pathology. Consequently, the study of monogenic disorders related to autism, such as neurofibromatosis type 1 (NF1), represents a promising approach to isolate mechanisms underlying ASD-related cognitive disabilities. However, the NF1 mouse model showed increased γ-aminobutyric acid (GABA) neurotransmission, whereas the human disease showed reduced cortical GABA levels. It is therefore important to clarify whether the E/I imbalance hypothesis holds true. We hypothesize that E/I may depend on distinct pre- and postsynaptic push-pull mechanisms that might be are region-dependent.MethodsIn current study, we assessed two critical components of E/I regulation: the concentration of neurotransmitters and levels of GABA(A) receptors. Measurements were performed across the hippocampi, striatum, and prefrontal cortices by combined in vivo magnetic resonance spectroscopy (MRS) and molecular approaches in this ASD-related animal model, the Nf1+/− mouse.ResultsCortical and striatal GABA/glutamate ratios were increased. At the postsynaptic level, very high receptor GABA(A) receptor expression was found in hippocampus, disproportionately to the small reduction in GABA levels. Gabaergic tone (either by receptor levels change or GABA/glutamate ratios) seemed therefore to be enhanced in all regions, although by a different mechanism.ConclusionsOur data provides support for the hypothesis of E/I imbalance in NF1 while showing that pre- and postsynaptic changes are region-specific. All these findings are consistent with our previous physiological evidence of increased inhibitory tone. Such heterogeneity suggests that therapeutic approaches to address neurochemical imbalance in ASD may need to focus on targets where convergent physiological mechanisms can be found.

AnkG hemizygous mice present cognitive impairment and elevated anxiety/depressive-like traits associated with decreased expression of GABA receptors and postsynaptic density protein.

Recent genome-wide association studies (GWAS) of patient populations and genetic linkage assessments have demonstrated that the ankyrin-G (AnkG) gene is involved in neuropsychiatric disorders, including bipolar disorder, schizophrenia, and Alzheimer's disease, but it remains unclear how the genetic variants of AnkG contribute to neuropsychiatric disorders. Here, we generated AnkG hemizygous mice using the gene trapping approach. Homozygous AnkG was embryonically lethal. Western blotting and real-time polymerase chain reaction (qPCR) assessments of wild type (WT) and AnkG +/- mutant mice demonstrated a 50% reduction of ANKG levels, at the gene and protein levels, in AnkG hemizygous mice. In behavioral tests, AnkG hemizygous mice exhibited elevated anxiety- and depression-like traits, as well as cognitive impairment. Moreover, the expression levels of cognitive-related proteins (including metabotropic glutamate receptor subtype-1, brain-derived neurotrophic factor, postsynaptic density-95, GABA-B receptor, and GABA-A receptor alpha-1) were significantly decreased (P<0.05), suggesting a possible role for AnkG in cognition. It is possible that the loss of AnkG in the brain disrupts the excitation/inhibition balance of neurotransmitters, hindering the synaptic plasticity of neurons, and consequently leading to abnormal behavioral symptoms. Therefore, AnkG possibly contributes to neuroprotection and normal brain function, and may constitute a new target for treating neuropsychiatric diseases, especially cognitive dysfunction.

Formation of GABAergic Neural Networks in the Bötzinger Complex in Rats in the Early Postnatal Period in Normal Conditions and with Prenatal Deficiency of Endogenous Serotonin

The dynamics of the distribution of GABAergic neurons and neurons expressing different types of GABA receptors (GABA-Aα1 and GABA-B1) in the Botzinger complex during the early postnatal period (the period of functional maturation of the receptor system in mammals) were studied in normal conditions and after prenatal reductions in serotonin content in Wistar rats. Brains from rat pups of two groups were studied on days 5, 9, and 20 after birth: controls (n = 9), born to intact females, and experimental (n = 13), born to mothers treated with parachlorophenylalanine during pregnancy to decrease endogenous serotonin content. GABA-synthesizing neurons and neurons expressing GABA-Aα1 and GABA-B1 receptors were detected immunocytochemically. Maturation of the inhibitory GABAergic network in the Botzinger complex occurred during the early postnatal period (by day 9). GABA production occurred simultaneously with GABA-Aα1 and GABA-B1 expression, though their maturation differed. GABA-Aα1 receptors formed earlier (by day 9) and coincided in time with GABA expression. Maturation of GABA-B1 receptors occurred later – only by week 3. Prenatal serotonin deficit led to a delay in the expression of GABA and GABA-Aα1 receptors in neurons of this nucleus and produced impairment to the formation of a network of terminals and synapses containing GABA and GABA-Aα1 and GABA-B1 receptors.

TOLERATING UNCERTAINTY IN OCD, DO PATIENTS REQUIRE MORE INFORMATION TO MAKE DECISIONS?

In addition to important metabolic functions in the brain, GABA is a neurotransmitter of major significance, being released by up to 40% of neurons to activate chloride channels resulting generally in inhibition of neuronal firing. Its ubiquitous presence in the brain and spinal cord means that almost all neurons either release GABA, express GABA receptors, or are innervated by neurons that do. GABA mechanisms are thought to be involved in anesthesia, anxiety, epilepsy, memory, neurodegenerative disorders, schizophrenia, sleep, stress, cardiovascular, and neuroendocrine function. Many agents act through GABA mechanisms including barbiturates, benzodiazepines, ethanol, flavonoids, general anesthetics, and neuroactive steroids.

Hippocampal low-frequency stimulation inhibits afterdischarge and increases GABA (A) receptor expression in amygdala-kindled pharmacoresistant epileptic rats

Objective: The purpose of the present study was to observe the effects of hippocampal low-frequency stimulation (Hip-LFS) on amygdala afterdischarge and GABA (A) receptor expression in pharmacoresistant epileptic (PRE) rats.Methods: A total of 110 healthy adult male Wistar rats were used to generate a model of epilepsy by chronic stimulation of the amygdala. Sixteen PRE rats were selected from 70 amygdala-kindled rats by testing their response to Phenytoin and Phenobarbital, and they were randomly assigned to a pharmacoresistant stimulation group (PRS group, 8 rats) or a pharmacoresistant control group (PRC group, 8 rats). A stimulation electrode was implanted into the hippocampus of all of the rats. Hip-LFS was administered twice per day in the PRS group for two weeks. Simultaneously, amygdala stimulus-induced seizures and afterdischarge were recorded. After the hippocampal stimulation was terminated, the brain tissues were obtained to determine the GABA (A) receptors by a method of immumohistochemistry and a real-time polymerase chain reaction.Results: The stages and duration of the amygdala stimulus-induced epileptic seizures were decreased in the PRS group. The afterdischarge threshold was increased and the duration as well as the afterdischarge frequency was decreased. Simultaneously, the GABA (A) expression was significantly increased in the PRS group.Conclusions: Hip-LFS may inhibit amygdala stimulus-induced epileptic seizures and up-regulate GABA (A) receptor expression in PRE rats. The antiepileptic effects of hippocampal stimulation may be partly achieved by increasing the GABA (A) receptor.

Cucurbitacin IIa exerts antidepressant-like effects on mice exposed to chronic unpredictable mild stress

Cucurbitacin IIa (CuIIa) is the major active component of the Helmseya amabilis root and is known to have antiviral and anti-inflammatory effects. In this study, we examined the antidepressant-like effects of CuIIa in a mouse model of chronic unpredictable mild stress (CUMS) and investigated the possible underlying mechanisms. To evaluate the antidepressant-like effects of CuIIa on depression-like behaviors, mice were subjected to the open-field test, the elevated plus-maze test, the forced-swimming test, and the tail-suspension test. We found that CuIIa treatment reversed the CUMS-induced behavioral abnormalities. Western blot analyses showed that CUMS significantly decreased brain-derived neurotrophic factor (BDNF) levels, cAMP-response element binding protein (CREB), and calcium/calmodulin-dependent protein kinase II (CaMKII) phosphorylation, and N-methyl-D-aspartate receptor subtype GluN2B and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor GluA1 expression in the amygdala; in addition, the expression of gamma-aminobutyric acid receptor A subunit α2 was upregulated in CUMS mice. These CUMS-induced changes were all normalized by CuIIa treatment and administration of the BDNF antagonist ANA-12 can block the antidepressant effect of CuIIa. Our findings suggest that the antidepressant-like effects of CuIIa may be exerted by regulation of the CaMKIIα-CREB-BDNF pathway and the balance between excitatory and inhibitory synaptic transmission in the amygdala.

Rho-kinase inhibitor prevents acute injury against transient focal cerebral ischemia by enhancing the expression and function of GABA receptors in rats

Studies have shown hydroxyfasudil-mediated inhibition of Rho-kinase (ROCK) has efficacy in rodent models of focal ischemia and in in vitro systems that recapitulate stroke conditions. However, the mechanisms underlying the neuroprotective effects of the ROCK inhibitor on stroke are not well understood. In this study, we examined the role of γ-aminobutyric acid (GABA) interneurons in the effects of hydroxyfasudil on transient middle cerebral artery occlusion (tMCAO) induced acute ischemia-reperfusion injury to explore the mechanisms. tMCAO rats developed marked neurological deficits and impaired long-term potentiation; these effects were attenuated by hydroxyfasudil. Expression of GABAA and GABAB receptors after ischemia was decreased to various extents in three brain regions: the cortex, hippocampus, and striatum. Hydroxyfasudil up-regulated expression in the cortex and hippocampus but not in the striatum. Moreover, hydroxyfasudil could suppress the activation of nuclear factor-κB (NF-κB) in these regions during the acute ischemia. We further found that in tMCAO rats, hydroxyfasudil was able to abolish the decrease in GABAA and GABAB receptor phosphorylation triggered by high-frequency stimulation as well as the activation of phosphatase and tensin homolog deleted on chromosome 10 (PTEN). In summary, our results suggest ROCK inhibition improved neurological function and mitigated synaptic plasticity deficits caused by transient focal cerebral ischemia through the inactivation of two distinct pathways: (1) a ROCK-NF-κB pathway that leads to the suppression of GABAA and GABAB expression, and (2) a ROCK-PTEN pathway that decreases the phosphorylation of GABAA and GABAB, thereby affecting receptor function by triggering receptor endocytosis and the degradation of internalized receptors.

Lost in translation? The potential psychobiotic Lactobacillus rhamnosus (JB-1) fails to modulate stress or cognitive performance in healthy male subjects

BackgroundPreclinical studies have identified certain probiotics as psychobiotics – live microorganisms with a potential mental health benefit. Lactobacillus rhamnosus (JB-1) has been shown to reduce stress-related behaviour, corticosterone release and alter central expression of GABA receptors in an anxious mouse strain. However, it is unclear if this single putative psychobiotic strain has psychotropic activity in humans. Consequently, we aimed to examine if these promising preclinical findings could be translated to healthy human volunteers. ObjectivesTo determine the impact of L. rhamnosus on stress-related behaviours, physiology, inflammatory response, cognitive performance and brain activity patterns in healthy male participants. MethodsAn 8week, randomized, placebo-controlled, cross-over design was employed. Twenty-nine healthy male volunteers participated. Participants completed self-report stress measures, cognitive assessments and resting electroencephalography (EEG). Plasma IL10, IL1β, IL6, IL8 and TNFα levels and whole blood Toll-like 4 (TLR-4) agonist-induced cytokine release were determined by multiplex ELISA. Salivary cortisol was determined by ELISA and subjective stress measures were assessed before, during and after a socially evaluated cold pressor test (SECPT). ResultsThere was no overall effect of probiotic treatment on measures of mood, anxiety, stress or sleep quality and no significant effect of probiotic over placebo on subjective stress measures, or the HPA response to the SECPT. Visuospatial memory performance, attention switching, rapid visual information processing, emotion recognition and associated EEG measures did not show improvement over placebo. No significant anti-inflammatory effects were seen as assessed by basal and stimulated cytokine levels. ConclusionsL. rhamnosus was not superior to placebo in modifying stress-related measures, HPA response, inflammation or cognitive performance in healthy male participants. These findings highlight the challenges associated with moving promising preclinical studies, conducted in an anxious mouse strain, to healthy human participants. Future interventional studies investigating the effect of this psychobiotic in populations with stress-related disorders are required.

Toluene inhalation in adolescent rats reduces flexible behaviour in adulthood and alters glutamatergic and GABAergic signalling.

Toluene is a commonly abused inhalant that is easily accessible to adolescents. Despite the increasing incidence of use, our understanding of its long-term impact remains limited. Here, we used a range of techniques to examine the acute and chronic effects of toluene exposure on glutameteric and GABAergic function, and on indices of psychological function in adult rats after adolescent exposure. Metabolomics conducted on cortical tissue established that acute exposure to toluene produces alterations in cellular metabolism indicative of a glutamatergic and GABAergic profile. Similarly, invitro electrophysiology in Xenopus oocytes found that acute toluene exposure reduced NMDA receptor signalling. Finally, in an adolescent rodent model of chronic intermittent exposure to toluene (10000ppm), we found that, while toluene exposure did not affect initial learning, it induced a deficit in updating that learning when response-outcome relationships were reversed or degraded in an instrumental conditioning paradigm. There were also group differences when more effort was required to obtain the reward; toluene-exposed animals were less sensitive to progressive ratio schedules and to delayed discounting. These behavioural deficits were accompanied by changes in subunit expression of both NMDA and GABA receptors in adulthood, up to 10weeks after the final exposure to toluene in the hippocampus, prefrontal cortex and ventromedial striatum; regions with recognized roles in behavioural flexibility and decision-making. Collectively, our data suggest that exposure to toluene is sufficient to induce adaptive changes in glutamatergic and GABAergic systems and in adaptive behaviour that may underlie the deficits observed following adolescent inhalant abuse, including susceptibility to further drug-use.

FORMATION OF GABA-ERGIC NEURAL NETWORK IN BÖTZINGER COMPLEX IN RATS DURING EARLY POSTNATAL PERIOD IN NORM AND IN PRENATAL DEFICIENCY OF ENDOGENOUS SEROTONIN

The dynamics of the distribution of GABAergic neurons and neurons expressing different types of GABA receptors (GABAAα1 and GABAB1) was studied in Bötzingercomplex (BötC) in the early postnatal period (the period of functional maturation of the respiratory system in mammals) in norm and prenatal reduction of serotonin content in Wistar rats. The brain was studied on postnatal Days 5, 9 and 20 in two groups of rat pups: control (n=9), born by intact females, and experimental (n=13), born from mothers that received parachlorophenylalanine, causing the depression of endogenous serotonin level. Imunocytochemical methods were used to detect the neurons producing GABA and expressing GABA and GABA Aα1B1 receptors. It was shown that the maturation of the inhibitory GABAergic network in BötC occurred in the early postnatal period (by Day 9). Simultaneously with GABA, the expression of GABA and GABA Aα1B1 receptors took place, however their maturation has the distinctive features. The formation of GABAAα1 receptors occurred earlier (by Day 9) and coincided in time with the expression of GABA. The maturation of GABAB1 receptors happened later - only by the third week. Prenatal serotonin deficiency caused a delay in the expression of GABA and GABAAα1 receptors by the neurons of BötC, as well as the disruption of the formation of a network of terminals and synapses containing GABA, GABAAα1 and GABAB1 receptors.

Hyperammonemia induces glial activation, neuroinflammation and alters neurotransmitter receptors in hippocampus, impairing spatial learning: reversal by sulforaphane.

BackgroundPatients with liver cirrhosis and minimal hepatic encephalopathy (MHE) show mild cognitive impairment and spatial learning dysfunction. Hyperammonemia acts synergistically with inflammation to induce cognitive impairment in MHE. Hyperammonemia-induced neuroinflammation in hippocampus could contribute to spatial learning impairment in MHE. Two main aims of this work were: (1) to assess whether chronic hyperammonemia increases inflammatory factors in the hippocampus and if this is associated with microglia and/or astrocytes activation and (2) to assess whether hyperammonemia-induced neuroinflammation in the hippocampus is associated with altered membrane expression of glutamate and GABA receptors and spatial learning impairment. There are no specific treatments for cognitive alterations in patients with MHE. A third aim was to assess whether treatment with sulforaphane enhances endogenous the anti-inflammatory system, reduces neuroinflammation in the hippocampus of hyperammonemic rats, and restores spatial learning and if normalization of receptor membrane expression is associated with learning improvement.MethodsWe analyzed the following in control and hyperammonemic rats, treated or not with sulforaphane: (1) microglia and astrocytes activation by immunohistochemistry, (2) markers of pro-inflammatory (M1) (IL-1β, IL-6) and anti-inflammatory (M2) microglia (Arg1, YM-1) by Western blot, (3) membrane expression of GABA, AMPA, and NMDA receptors using the BS3 cross-linker, and (4) spatial learning using the radial maze.ResultsThe results reported show that hyperammonemia induces astrocytes and microglia activation in the hippocampus, increasing pro-inflammatory cytokines IL-1β and IL-6. This is associated with altered membrane expression of AMPA, NMDA, and GABA receptors which would be responsible for altered neurotransmission and impairment of spatial learning in the radial maze. Treatment with sulforaphane promotes microglia differentiation from pro-inflammatory M1 to anti-inflammatory M2 phenotype and reduces activation of astrocytes in hyperammonemic rats. This reduces neuroinflammation, normalizes membrane expression of glutamate and GABA receptors, and restores spatial learning in hyperammonemic rats.ConclusionsHyperammonemia-induced neuroinflammation impairs glutamatergic and GABAergic neurotransmission by altering membrane expression of glutamate and GABA receptors, resulting in impaired spatial learning. Sulforaphane reverses all these effects. Treatment with sulforaphane could be useful to improve cognitive function in cirrhotic patients with minimal or clinical hepatic encephalopathy.

Verification of γ-Amino-Butyric Acid (GABA) Signaling System Components in Periodontal Ligament Cells In Vivo and In Vitro.

CNS key neurotransmitter γ-amino-butyric acid (GABA) and its signaling components are likewise detectable in non-neuronal tissues displaying inter alia immunomodulatory functions. This study aimed at identifying potential glutamate decarboxylase (GAD)65 and GABA receptor expression in periodontal ligament (PDL) cells in vivo and in vitro, with particular regard to inflammation and mechanical loading. Gene expression was analyzed in human PDL cells at rest or in response to IL-1ß (5ng/ml) or TNFα (5ng/ml) challenge via qRT-PCR. Western blot determined constitutive receptor expression, and confocal laser scanning fluorescence microscopy visualized expression changes induced by inflammation. ELISA quantified GAD65 release. Immunocytochemistry was performed for GABA component detection in vitro on mechanically loaded PDL cells, and in vivo on rat upper jaw biopsies with mechanically induced root resorptions. Statistical significance was set at p<0.05. GABAB1, GABAB2, GABAA1, and GABAA3 were ubiquitously expressed both on gene and protein level. GABAA2 and GAD65 were undetectable in resting cells, but induced by inflammation. GABAB1 exhibited the highest basal gene expression (6.97%±0.16). IL-1ß markedly increased GABAB2 on a transcriptional (57.28-fold±12.40) and protein level seen via fluorescence microscopy. TNFα-stimulated PDL cells released GAD65 (3.68pg/ml±0.17 after 24h, 5.77pg/ml±0.65 after 48h). Immunocytochemistry revealed GAD65 expression in mechanically loaded PDL cells. In vivo, GABA components were varyingly expressed in an inflammatory periodontal environment. PDL cells differentially express GABA signaling components and secrete GAD65. Inflammation and mechanical loading regulate these neurotransmitter molecules, which are also detectable in vivo and are potentially involved in periodontal pathophysiology.

Prefrontal cortical GABAergic signaling and impaired behavioral flexibility in aged F344 rats

The prefrontal cortex (PFC) is critical for the ability to flexibly adapt established patterns of behavior in response to a change in environmental contingencies. Impaired behavioral flexibility results in maladaptive strategies such as perseveration on response options that no longer produce a desired outcome. Pharmacological manipulations of prefrontal cortical GABAergic signaling modulate behavioral flexibility in animal models, and prefrontal cortical interneuron dysfunction is implicated in impaired behavioral flexibility that accompanies neuropsychiatric disease. As deficits in behavioral flexibility also emerge during the normal aging process, the goal of this study was to determine the role of GABAergic signaling, specifically via prefrontal cortical GABA(B) receptors, in such age-related deficits. Young and aged rats were trained in a set shifting task performed in operant chambers. First, rats learned to discriminate between two response levers to obtain a food reward on the basis of a cue light illuminated above the correct lever. Upon acquisition of this initial discrimination, the contingencies were shifted such that rats had to ignore the cue light and respond on the levers according to their left/right positions. Both young and aged rats acquired the initial discrimination similarly; however, aged rats were impaired relative to young following the set shift. Among aged rats, GABA(B) receptor expression in the medial prefrontal cortex (mPFC) was strongly correlated with set shifting, such that lower expression was associated with worse performance. Subsequent experiments showed that intra-mPFC administration of the GABA(B) receptor agonist baclofen enhanced set shifting performance in aged rats. These data directly link GABAergic signaling via GABA(B) receptors to impaired behavioral flexibility associated with normal aging.

Unitary GABAergic volume transmission from individual interneurons to astrocytes in the cerebral cortex.

Communication between individual GABAergic cells and their target neurons is mediated by synapses and, in the case of neurogliaform cells (NGFCs), by unitary volume transmission. Effects of non-synaptic volume transmission might involve non-neuronal targets, and astrocytes not receiving GABAergic synapses but expressing GABA receptors are suitable for evaluating this hypothesis. Testing several cortical interneuron types in slices of the rat cerebral cortex, we show selective unitary transmission from NGFCs to astrocytes with an early, GABAA receptor and GABA transporter-mediated component and a late component that results from the activation of GABA transporters and neuronal GABAB receptors. We could not detect Ca2+ influx in astrocytes associated with unitary GABAergic responses. Our experiments identify a presynaptic cell-type-specific, GABA-mediated communication pathway from individual neurons to astrocytes, assigning a role for unitary volume transmission in the control of ionic and neurotransmitter homeostasis.

Classifying neuronal subclasses of the cerebellum through constellation pharmacology.

A pressing need in neurobiology is the comprehensive identification and characterization of neuronal subclasses within the mammalian nervous system. To this end, we used constellation pharmacology as a method to interrogate the neuronal and glial subclasses of the mouse cerebellum individually and simultaneously. We then evaluated the data obtained from constellation-pharmacology experiments by cluster analysis to classify cells into neuronal and glial subclasses, based on their functional expression of glutamate, acetylcholine, and GABA receptors, among other ion channels. Conantokin peptides were used to identify N-methyl-d-aspartate (NMDA) receptor subtypes, which revealed that neurons of the young mouse cerebellum expressed NR2A and NR2B NMDA receptor subunits. Additional pharmacological tools disclosed differential expression of α-amino-3-hydroxy-5-methyl-4-isoxazloepropionic, nicotinic acetylcholine, and muscarinic acetylcholine receptors in different neuronal and glial subclasses. Certain cell subclasses correlated with known attributes of granule cells, and we combined constellation pharmacology with genetically labeled neurons to identify and characterize Purkinje cells. This study illustrates the utility of applying constellation pharmacology to classify neuronal and glial subclasses in specific anatomical regions of the brain.

Axon-to-Glia Interaction Regulates GABAA Receptor Expression in Oligodendrocytes

Myelination requires oligodendrocyte-neuron communication, and both neurotransmitters and contact interactions are essential for this process. Oligodendrocytes are endowed with neurotransmitter receptors whose expression levels and properties may change during myelination. However, only scant information is available about the extent and timing of these changes or how they are regulated by oligodendrocyte-neuron interactions. Here, we used electrophysiology to study the expression of ionotropic GABA, glutamate, and ATP receptors in oligodendrocytes derived from the optic nerve and forebrain cultured either alone or in the presence of dorsal root ganglion neurons. We observed that oligodendrocytes from both regions responded to these transmitters at 1 day in culture. After the first day in culture, however, GABA sensitivity diminished drastically to less than 10%, while that of glutamate and ATP remained constant. In contrast, the GABA response amplitude was sustained and remained stable in oligodendrocytes cocultured with dorsal root ganglion neurons. Immunochemistry and pharmacological properties of the responses indicated that they were mediated by distinctive GABAA receptors and that in coculture with neurons, the oligodendrocytes bearing the receptors were those in direct contact with axons. These results reveal that GABAA receptor regulation in oligodendrocytes is driven by axonal cues and that GABA signaling may play a role in myelination and/or during axon-glia recognition.

Sildenafil reduces neuroinflammation and restores spatial learning in rats with hepatic encephalopathy: underlying mechanisms.

BackgroundThere are no specific treatments for the neurological alterations of cirrhotic patients with minimal hepatic encephalopathy (MHE). Rats with MHE due to portacaval shunt (PCS) show impaired spatial learning. The underlying mechanisms remain unknown. The aims of this work were to assess: (a) whether PCS rats show neuroinflammation in hippocampus, (b) whether treatment with sildenafil reduces neuroinflammation and restores spatial learning in PCS rats, and (c) analyze the underlying mechanisms.MethodsNeuroinflammation was assessed by determining inflammatory markers by Western blot. Phosphorylation of MAP-kinase p38 was assessed by immunohistochemistry. Membrane expression of GABA and glutamate receptors was analyzed using BS3 cross-linker. Spatial learning was analyzed using the radial and Morris water mazes. To assess if sildenafil reverses the alterations, rats were treated with sildenafil in the drinking water.ResultsPCS rats show increased IL-1β and TNF-α levels and phosphorylation (activity) of p38 in hippocampus. Membrane expression of subunits α1 of GABAA receptor and GluR2 of AMPA receptor are increased in PCS rats, while subunits GluR1 of AMPA receptors and NR1 and NR2a of NMDA receptors are reduced. PCS rats show reduced spatial learning in the radial and Morris water mazes. Sildenafil treatment normalizes IL-1β and TNF-α levels, p38 phosphorylation, and membrane expression of GABAA, AMPA, and NMDA receptors and restores spatial learning.ConclusionsIncreased IL-1β alters GABAergic and glutamatergic neurotransmission in hippocampus and impairs spatial learning in rats with MHE. Sildenafil reduces neuroinflammation and restores learning. Phosphodiesterase-5 inhibitors may be useful to improve cognitive function in patients with MHE.