The protein kinase C[beta]-selective inhibitor, enzastaurin, attenuates amphetamine-stimulated locomotor activity and self-administration behaviors in rats

Rationale Pathological amphetamine (AMPH) use is a serious public health concern with no pharmacological treatment options. Protein kinase C[beta] (PKC[beta]) has been implicated in the mechanism of action of AMPH, such that inhibition of PKC[beta] attenuates AMPH-stimulated dopamine efflux in vivo. With this in mind, inhibition of PKC[beta] may be a viable therapeutic target for AMPH use disorder. Objective The purpose of this study is to demonstrate that selective pharmacological inhibition of PKC[beta] alters AMPH-stimulated behaviors in rats. Methods Rats were administered intracerebroventricular (i.c.v.) injections of the PKC[beta]-selective inhibitor enzastaurin 0.5, 3, 6, or 18 h before evaluating AMPH-stimulated locomotion (0.32-3.2 mg/kg). Rats were trained to make responses for different doses of AMPH infusions or sucrose under a fixed ratio 5 schedule of reinforcement, and the effects of enzastaurin pretreatment 3 or 18 h prior to a self-administration session were determined. Also, the effect of enzastaurin on AMPH-stimulated PKC activity in the ventral striatum was evaluated. Results A large dose of enzastaurin (1 nmol) decreased AMPH-stimulated locomotor activity 0.5 h following enzastaurin administration. Small doses of enzastaurin (10-30 pmol) attenuated AMPH-stimulated locomotor activity and shifted the AMPH dose-effect curve to the right following an 18-h pretreatment. Rats pretreated with enzastaurin 18 h, but not 3, prior to a self-administration session showed a decrease in the number of responses for AMPH, shifted the ascending limb of the amphetamine dose effect curve, and produced no change in responses for sucrose. AMPH-stimulated PKC activity was decreased following a 0.5- or 18-h pretreatment, but not a 3-h pretreatment of enzastaurin. Conclusions These results demonstrate that inhibition of PKC[beta] will decrease AMPH-stimulated behaviors and neurobiological changes and suggest that PKC[beta] is potentially a viable target for AMPH use disorder.