Cocaine-induced Hyperactivity and Sensitization Are Dependent on GSK3

Glycogen synthase kinase 3 (GSK3) is a critical mediator of many intracellular signaling systems. The activity of GSK3 is regulated by several kinases, with inactivation occurring via phosphorylation of the inhibitory serine-21 (alpha-isoform) and serine-9 (beta-isoform) residues. Here, we investigated whether acute cocaine administration regulates GSK3 activity and if inhibition of GSK3 by valproate or the selective GSK3 inhibitor SB 216763 would attenuate cocaine-induced behaviors in mice. Mice injected with cocaine (20 mg/kg, i.p.) showed a reduction in the phosphorylation of GSK3beta in the caudate putamen, reflecting an increase in the activity of the kinase. To assess the role of GSK3 in cocaine-induced hyperactivity, mice were pretreated with valproate (50-300 mg/kg, i.p.), SB 216763 (0.25-7.5 mg/kg, i.p.), or the appropriate vehicle prior to saline or cocaine (20 mg/kg, i.p.). Valproate or SB 216763 produced significant dose-dependent reductions in cocaine-induced ambulatory and stereotypic activity. Repeated administration of cocaine can result in an augmentation of the locomotor-stimulatory effects of the drug, a phenomenon referred to as sensitization. Mice pretreated with SB 216763 (2.5 mg/kg, i.p.) prior to daily cocaine (20 mg/kg, i.p.) for 5 days showed a significant attenuation of the development of cocaine-induced behavioral sensitization following a cocaine challenge on day 13. These results indicate that cocaine activated GSK3beta in the caudate putamen and that pharmacological inhibition of GSK3 reduced both the acute behavioral responses to cocaine and the long-term neuroadaptations produced by repeated cocaine, therefore suggesting a role for GSK3 in the behavioral and neurochemical manifestations associated with cocaine exposure.