Repeated orexin 1 receptor antagonism effects on cocaine seeking in rats.

The orexin/hypocretin system has been implicated in multiple phases of drug addiction. Acute orexin receptor blockade with the orexin-1 receptor (OX1R) antagonist, SB-334867, has been found to reduce cocaine seeking after cocaine self-administration. As repeated drug dosing can have differential effects and is more clinically relevant than acute dosing, in the current study we examined the effects of repeated SB-334867 on cocaine self-administration, extinction, and reinstatement to cocaine seeking in Sprague-Dawley rats. We found that repeated SB-334867 (10 mg/kg/day) had no effect on established cocaine self-administration. Repeated SB-334867 (both 10 and 20 mg/kg) attenuated cocaine seeking during extinction; however, this effect was only observed when animals had no prior experience with SB-334867 and when SB-334867 was administered prior to, but not after, daily extinction sessions. Notably, daily treatment with SB-334867 (10 mg/kg) during extinction increased subsequent cue-induced reinstatement, whereas repeated SB-334867 (20 mg/kg) administration during extinction enabled acute SB-334867 to reduce cue-induced reinstatement. Repeated SB-334867 treatment (10 or 20 mg/kg) failed to affect reinstatement induced by priming injections of cocaine (10 mg/kg). These results show that repeated inhibition of OX1R-mediated signaling exerts a lasting and specific role in mediating environmentally activated cocaine seeking.