Single Ethanol Withdrawal Regulates Extrasynaptic δ-GABAA Receptors Via PKCδ Activation

Alcohol (ethanol, EtOH) is one of the most widely abused drugs with profound effects on brain function and behavior. GABA(A) receptors (GABA(A)Rs) are one of the major targets for EtOH in the brain. Temporary plastic changes in GABA(A)Rs after withdrawal from a single EtOH exposure occur both in vivo and in vitro, which may be the basis for chronic EtOH addiction, tolerance and withdrawal symptoms. Extrasynaptic delta-GABA(A)R endocytosis is implicated in EtOH-induced GABA(A)R plasticity, but the mechanisms by which the relative abundance and localization of specific GABA(A)Rs are altered by EtOH exposure and withdrawal remain unclear. In this study, we investigated the mechanisms underlying rapid regulation of extrasynaptic delta-GABA(A)R by a single EtOH withdrawal in cultured rat hippocampal neurons. Thirty-minutes EtOH (60 mM) exposure increased extrasynaptic tonic current (I-tonic) amplitude without affecting synaptic GABA(A)R function in neurons. In contrast, at 30 min after withdrawal, I-tonic amplitude and responsiveness to acute EtOH were both reduced. Similar results occurred in neurons with okadaic acid (OA) or phorbol 12,13-dibutyrate (PDBu) exposure. Protein kinase C (PKC) inhibition prevented the reduction of I-tonic amplitude and the tolerance to acute EtOH, as well as the reduction of GABA(A)R-delta subunit abundance induced by a single EtOH withdrawal. Moreover, EtOH withdrawal selectively increased PKC delta level, whereas PKC delta inhibition specifically rescued the EtOH-induced alterations in GABA(A)R-delta subunit level and delta-GABA(A)R function. Together, we provided strong evidence for the important roles of PKC din the rapid regulation of extrasynaptic delta-GABA(A)R induced by a single EtOH withdrawal.