Cocaine Potentiates Multiple 5-HT_2A Receptor Signaling Pathways and Is Associated with Decreased Phosphorylation of 5-HT_2A Receptors In Vivo

Cocaine addiction is a chronic relapsing disorder in which the underlying mechanisms are not well understood. Here, we used Sprague-Dawley rats injected with either saline (1 ml/kg) or cocaine (15 mg/kg) for 7 days (b.i.d, i.p) to study the effect of cocaine on several components of 5-HT_2A receptor signaling in prefrontal cortex (PFCx). We detected enhanced activation of 5-HT_2A receptor-mediated phospholipase C beta (PLCβ) and extracellular regulated kinase 1/2 activity in PFCx of cocaine-treated rats. Although we were unable to detect changes in the protein levels of several proteins associated with 5-HT_2A receptor signaling such as caveolin-1, postsynaptic density protein 95, β-arrestin 2, etc., we found a significant reduction in the phosphorylation status of cortical 5-HT_2A receptors. This phenomenon was associated with reduced levels of G-protein receptor kinase 5 (GRK5), but not GRK2 or RSK2, proteins. Our results suggest that decreased phosphorylation of 5-HT_2A receptors could mediate, at least in part, the cocaine-induced potentiation of multiple 5-HT_2A receptor signaling pathways in rat PFCx. As discussed in this manuscript, we hypothesize that preventing these neuroadaptations in 5-HT_2A receptor signaling may alleviate some of the aversive withdrawal-associated symptoms that contribute to relapse to cocaine abuse.