Atypical protein kinase C is a novel mediator of dopamine-enhanced firing in nucleus accumbens neurons.

Current concepts suggest that nucleus accumbens (NAcb) dopamine mediates several motivated and addictive behaviors. Although the role of protein kinase A (PKA) and dopamine and cyclic adenosine 3',5' monophosphate-regulated phosphoprotein 32 kDa in NAcb dopamine receptor throughput has been studied extensively, the contribution of protein kinase C (PKC) to NAcb firing is poorly understood. Here we show that dopamine-mediated enhancement of spike firing in NAcb shell medium spiny neurons was prevented by the PKC inhibitor bisindolylmaleimide but not by the phospholipase C inhibitor 1-[6-((17b-3-methoxyestra-1,3,5(10)-trien-17-yl) amino)hexyl]-1H-pyrrole-2,5-dione, suggesting a role for a diacylglycerol-independent atypical PKC (aPKC) isoform. In this regard, modulation of firing by dopamine was prevented by intracellular perfusion of a pseudosubstrate peptide inhibitor for aPKCs. We also provide evidence, using an in vitro kinase assay, that dopamine receptor activation increased aPKC activity in striatal membranes. Finally, direct activation of PKA with forskolin enhanced firing even during inhibition of aPKCs, suggesting that aPKCs acted upstream of PKA activation. Thus, aPKCs appear to mediate dopaminergic enhancement of spike firing in the NAcb shell, and may therefore play a critical role in NAcb- and dopamine-dependent goal-directed behaviors.