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GIT1 and ?PIX are essential for GABA(A) receptor synaptic stability and inhibitory neurotransmission.

ABSTRACT: Effective inhibitory synaptic transmission requires efficient stabilization of GABA(A) receptors (GABA(A)Rs) at synapses, which is essential for maintaining the correct excitatory-inhibitory balance in the brain. However, the signaling mechanisms that locally regulate synaptic GABA(A)R membrane dynamics remain poorly understood. Using a combination of molecular, imaging, and electrophysiological approaches, we delineate a GIT1/?PIX/Rac1/PAK signaling pathway that modulates F-actin and is important for maintaining surface GABA(A)R levels, inhibitory synapse integrity, and synapse strength. We show that GIT1 and ?PIX are required for synaptic GABA(A)R surface stability through the activity of the GTPase Rac1 and downstream effector PAK. Manipulating this pathway using RNAi, dominant-negative and pharmacological approaches leads to a disruption of GABA(A)R clustering and decrease in the strength of synaptic inhibition. Thus, the GIT1/?PIX/Rac1/PAK pathway plays a crucial role in regulating GABA(A)R synaptic stability and hence inhibitory synaptic transmission with important implications for inhibitory plasticity and information processing in the brain.

SUBMITTER: Smith KR

PROVIDER: S-EPMC4536293 | biostudies-literature | 2014 Oct

REPOSITORIES: biostudies-literature

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GIT1 and βPIX are essential for GABA(A) receptor synaptic stability and inhibitory neurotransmission.

Smith Katharine R KR Davenport Elizabeth C EC Wei Jing J Li Xiangning X Pathania Manavendra M Vaccaro Victoria V Yan Zhen Z Kittler Josef T JT

Cell reports 20141002 1

Effective inhibitory synaptic transmission requires efficient stabilization of GABA(A) receptors (GABA(A)Rs) at synapses, which is essential for maintaining the correct excitatory-inhibitory balance in the brain. However, the signaling mechanisms that locally regulate synaptic GABA(A)R membrane dynamics remain poorly understood. Using a combination of molecular, imaging, and electrophysiological approaches, we delineate a GIT1/βPIX/Rac1/PAK signaling pathway that modulates F-actin and is importa ...[more]

PMID: 25284783

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Project description:BackgroundThe prefrontal cortex (PFC) acts as an integrative hub for the processing of cortical and subcortical input into meaningful efferent signaling, permitting complex associative behaviors. PFC dysfunction is consistently observed with ethanol (EtOH) dependence and is a core component of the pathology of alcohol use disorders in current models of addiction. While intracortical gamma-aminobutryric acid (GABA)ergic neurotransmission is understood to be essential for maintaining coordinated network activity within the cortex, relatively little is known regarding functional GABAergic adaptations in PFC during EtOH dependence.MethodsIn the present study, male and female (> postnatal day 60) Sprague-Dawley rats were administered EtOH (5.0 g/kg; intragastric gavage) for 14 to 15 consecutive days. Twenty-four hours after the final administration, animals were sacrificed and brains extracted for electrophysiological recordings of isolated GABAA receptor-mediated currents or analysis of GABAA receptor subunit protein expression in deep-layer PFC neurons.ResultsChronic EtOH exposure significantly attenuated activity-dependent spontaneous GABAA receptor-mediated inhibitory postsynaptic current (IPSC) frequency with no effect on amplitude. Furthermore, analysis of IPSC decay kinetics revealed a significant enhancement of IPSC decay time that was associated with decrements in expression of the α1 GABAA receptor subunit, indicative of further impaired phasic inhibition. These phenomena occurred irrespective of neuron projection destination and sex. Based on previous observations by our laboratory of an epigenetic mechanism for EtOH-induced changes in cortical GABAA receptor subunit expression, the histone deacetylase inhibitor Trichostatin A was administered to water- and EtOH-exposed animals, and prevented EtOH-induced changes in spontaneous IPSC frequency, IPSC decay kinetics, and GABAA receptor subunit expression.ConclusionsTaken together, these results demonstrate that chronic EtOH exposure impairs synaptic inhibitory neurotransmission in deep-layer pyramidal neurons of the medial PFC in both male and female rats. These maladaptations occur in neurons projecting to numerous regions implicated in the sequelae of EtOH dependence, offering a mechanistic link between the manifestation of PFC dysfunction and negative affective states observed with extended consumption.

Project description:ObjectiveDeficits in working memory and cognitive control in schizophrenia are associated with impairments in prefrontal cortical function, including altered gamma band oscillations. These abnormalities are thought to reflect a deficiency in the synchronization of pyramidal cell activity that is dependent, in part, on gamma-aminobutyric acid (GABA) neurotransmission through GABA type A (GABA(A)) receptors containing alpha(2) subunits. The authors conducted a proof-of-concept clinical trial designed to test the hypothesis that a novel compound with relatively selective agonist activity at GABA(A) receptors containing alpha(2) subunits would improve cognitive function and gamma band oscillations in individuals with schizophrenia.MethodParticipants were male subjects (N=15) with chronic schizophrenia who were randomly assigned to receive 4 weeks of treatment with the study drug MK-0777, a benzodiazepine-like agent with selective activity at GABA(A) receptors containing alpha(2) or alpha(3) subunits, or a matched placebo in a double-blind fashion. Outcome measures were the Brief Psychiatric Rating Scale (BPRS), Repeatable Battery for the Assessment of Neuropsychological Status, three tests of working memory and/or cognitive control (N-back, AX Continuous Performance Test, and Preparing to Overcome Prepotency), and EEG measures of gamma band oscillations induced during the Preparing to Overcome Prepotency task.ResultsCompared with placebo, the MK-0777 compound was associated with improved performance on the N-back, AX Continuous Performance Test, and Preparing to Overcome Prepotency tasks. The compound was also associated with increased frontal gamma band power during the Preparing to Overcome Prepotency task. No effects of the MK-0777 compound were detected in BPRS or Repeatable Battery for the Assessment of Neuropsychological Status scores, with the exception of improvement on the Repeatable Battery for the Assessment of Neuropsychological Status delayed memory index. The MK-0777 agent was well-tolerated.ConclusionsThese findings provide preliminary support for the hypothesis that enhanced GABA activity at alpha(2) subunit containing GABA(A) receptors improves behavioral and electrophysiological measures of prefrontal function in individuals with schizophrenia.

Dataset Information

GIT1 and ?PIX are essential for GABA(A) receptor synaptic stability and inhibitory neurotransmission.

Publications

GIT1 and βPIX are essential for GABA(A) receptor synaptic stability and inhibitory neurotransmission.

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