Activation of central neurokinin-1 receptors induces reinstatement of cocaine-seeking behavior

A number of neurochemical systems have been implicated in mediating relapse to drug-seeking behavior. Substance P (SP) is a neuropeptide that interacts with some of these systems, suggesting a possible role for SP and its preferred receptor, the neurokinin-1 (NK-1) receptor, in the mediation of relapse. In this study, we examined whether selective activation of NK-1 receptors induces reinstatement of cocaine-seeking behavior, and whether endogenous activity at these receptors is involved in mediating cocaine-induced reinstatement. For each experiment, rats were trained to self-administer cocaine for 8-10 days, and following a period of extinction, tests for reinstatement were given. To examine the effects of NK-1 receptor activation on reinstatement of cocaine-seeking behavior, animals received an intracerebroventricular (ICV) infusion of the selective NK-1 receptor agonist, [Sar(9)Met(O-2)(11)]-SP (0, 1, 3 mu g), immediately prior to the test session. To examine the role of endogenous NK-1 receptor activity on cocaine-induced reinstatement, rats were pretreated with ICV infusions of the selective NK-1 receptor antagonists, RP67580 (0, 0.1, 0.5, 2.5 nmol) or GR82334 (0,,2, 10, 50 pmol), prior to systemic priming injections of cocaine (10 mg/kg or 20 mg/kg; i.p.). The results showed that [Sar(9)Met(O-2)(11)]-SP induced reinstatement of cocaine-seeking behavior, but that RP67580 and GR82334 had no effect on cocaine-induced reinstatement. These findings suggest that while activation of NK-1 receptors is capable of inducing reinstatement of cocaine-seeking behavior, endogenous activity at these receptors is not involved in mediating the priming effects of cocaine on reinstatement of drug-seeking behavior. (C) 2005 Elsevier Ireland Ltd. All rights reserved.