Post-cocaine Changes in Regulator of G-protein Signaling (RGS) Proteins in the Dorsal Striatum: Relevance for Cocaine-seeking and Protein Kinase C-mediated Phosphorylation

Persistent cocaine-induced neuroadaptations within the cortico-striatal circuitry might be related to elevated risk of relapse observed in human addicts even after months or years of drug-free abstinence. Identification of these neuroadaptations may lead development of novel, neurobiologically-based treatments of relapse. In the current study, 12 adult male Sprague-Dawley rats self-administered cocaine (or received yoked-saline) for two weeks followed by three weeks of home-cage abstinence. At this point, we analyzed expression of proteins involved in regulation of Gαi- and Gαq-protein signaling in the dorsal striatum (dSTR). Animals abstinent from chronic cocaine showed decreased expression of regulator of G-protein signaling 2 (RGS2) and RGS4, as well as upregulation of RGS9. These data, together with the increased ratio of Gαq-to-Gαi proteins indicated, "sensitized" Gαq signaling in the dSTR of abstinent cocaine animals. To evaluate activation of Gαq signaling during relapse, another group of abstinent cocaine animals (and yoked saline controls, 22 rats together) was reintroduced to the cocaine context and PKC-mediated phosphorylation in the dSTR was analyzed. Re-exposure to the cocaine context triggered cocaine seeking and increase in phosphorylation of cellular PKC substrates, including phospho-ERK and phospho-CREB. In conclusion, this study demonstrates persistent dysregulation of RGS proteins in the dSTR of abstinent cocaine animals that may produce an imbalance in local Gαq-to-Gαi signaling. This imbalance might be related to augmented PKC-mediated phosphorylation during relapse to cocaine-seeking. Future studies will address whether selective targeting of RGS proteins in the dSTR can be utilized to suppress PKC-mediated phosphorylation and relapse to cocaine-seeking.