A role for casein kinase 1 epsilon in the locomotor stimulant response to methamphetamine

We previously colocalized a quantitative trait locus (QTL) for sensitivity to the locomotor stimulant effects of methamphetamine (MA) with a QTL for expression of casein kinase 1 epsilon (Csnk1-E >) in the nucleus accumbens (NAc). Subsequently, we identified a single nucleotide polymorphism in CSNK1E (rs135745) that was associated with increased sensitivity to the subjective effects of d-amphetamine in healthy human subjects. Based on these results, we hypothesized that differential expression of Csnk1-E > causes differential sensitivity to MA-induced locomotor activity in mice. In the present study, we used PF-670462 (PF), which is a selective inhibitor of Csnk1-E >, to directly evaluate the role of Csnk1-E > in the locomotor stimulant response to MA in male C57BL/6J mice. We administered vehicle, PF, MA, or MA + PF, either via intraperitoneal injections or bilateral intra-NAc microinjections. We also examined Darpp-32 phosphorylation in mice receiving intraperitoneal injections. Intraperitoneal PF (20-40 mg/kg) attenuated the locomotor stimulant response to MA (2 mg/kg) without affecting baseline activity. The high dose of PF also significantly inhibited MA-induced phosphorylation of Darpp-32, providing a potential mechanism by which Csnk1-E > contributes to MA-induced locomotor activity. Furthermore, microinjection of PF (5 mu g/side) into the NAc completely blocked the locomotor stimulant response to MA (2.5 mu g/side) without affecting baseline activity. These results provide direct evidence that Csnk1-E > is crucial for the locomotor stimulant response to a moderate dose of MA and suggest that genetic polymorphisms affecting Csnk1-E > expression or function could influence sensitivity to amphetamines in both mice and humans.