Attenuation of relapse to cocaine seeking by dopamine D1 receptor agonists and antagonists in non-human primates.

Rationale: Dopamine D(1) receptor agonists and antagonists attenuate reinstatement of cocaine seeking in a non-human primate model of relapse. The mechanisms by which these different classes of D(1) receptor drugs produce these similar effects on cocaine seeking are unknown.

Objectives: This study investigated how D(1) receptor agonists and antagonists alter the shape and position of the dose-response function for reinstatement of drug seeking induced by a cocaine prime accompanied by restoration of the cocaine-paired stimulus.

Methods: Squirrel monkeys were given extensive histories of cocaine self-administration under a second-order fixed-interval, fixed-ratio schedule of i.v. drug injection. Drug seeking was then extinguished by replacing cocaine with vehicle and eliminating the cocaine-paired stimulus. In subsequent test sessions, in which the cocaine-paired stimulus was re-introduced, priming injections of cocaine alone or combined with the different D(1) receptor high- and low-efficacy agonists and antagonists (SKF 82958, SKF 81297, SKF 83959, ecopipam; n=3-4 per drug condition) were tested for their ability to reinstate extinguished cocaine seeking.

Results: Cocaine priming accompanied by the restoration of the cocaine-paired stimulus induced a dose-dependent reinstatement of drug seeking. When combined with cocaine, all D(1) receptor agonists and antagonists produced rightward and downward shifts in the cocaine dose-response function. However, combined pretreatment of SKF81297 (agonist) and ecopipam (antagonist) inhibited cocaine seeking less than either drug individually.

Conclusions: These findings suggest that D(1) receptor high- and low-efficacy agonists as well as antagonists attenuate reinstatement of cocaine seeking in part via pharmacologically opposing actions at a common population of D(1) receptors.