GABAA receptor regulation of voluntary ethanol drinking requires PKCε

Protein kinase C (PKC) regulates a variety of neural functions, including ion channel activity, neurotransmitter release, receptor desensitization and differentiation. We have shown previously that mice lacking the E-isoform of PKC (PKC epsilon) self-administer 75% less ethanol and exhibit supersensitivity to acute ethanol and allosteric positive modulators of GABA(A) receptors when compared with wild-type controls. The purpose of the present study was to examine involvement of PKC epsilon in GABA(A) receptor regulation of voluntary ethanol drinking. To address this question, PKC epsilon null-mutant and wild-type control mice were allowed to drink ethanol (10% v/v) vs. water on a two-bottle continuous access protocol. The effects of diazepam (nonselective GABA(A) BZ positive modulator), zolpidem (GABA(A) alpha 1 agonist), L-655,708 (BZ-sensitive GABA(A) alpha 5 inverse agonist), and flumazenil (BZ antagonist) were then tested on ethanol drinking. Ethanol intake (grams/kg/day) by wild-type mice decreased significantly after diazepam or zolpidem but increased after L655,708 administration. Flumazenil antagonized diazepam-induced reductions in ethanol drinking in wild-type mice. However, ethanol intake by PKC epsilon null mice was not altered by any of the GABAergic compounds even though effects were seen on water drinking in these mice. Increased acute sensitivity to ethanol and diazepam, which was previously reported, was confirmed in PKC epsilon null mice. Thus, results of the present study show that PKC epsilon null mice do not respond to doses of GABA(A) BZ receptor ligands that regulate ethanol drinking by wild-type control mice. This suggests that PKC epsilon may be required for GABA(A) receptor regulation of chronic ethanol drinking.