Single Ethanol Withdrawal Regulates Extrasynaptic δ-GABA(A) 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 δ-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 δ-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-δ subunit abundance induced by a single EtOH withdrawal. Moreover, EtOH withdrawal selectively increased PKCδ level, whereas PKCδ inhibition specifically rescued the EtOH-induced alterations in GABA(A)R-δ subunit level and δ-GABA(A)R function. Together, we provided strong evidence for the important roles of PKCδ in the rapid regulation of extrasynaptic δ-GABA(A)R induced by a single EtOH withdrawal.