Antagonism at delta opioid receptors blocks cocaine's, but not morphine's, enhancement of responding for intracranial stimulation.

Rats were fixed with a chronically indwelling bipolar electrode for direct electrical stimulation of the medial forebrain bundle as it courses through the lateral hypothalamus. In Experiment 1, the rats were trained to self-stimulate (i.e., lever press) at each of 3 intensities of intracranial stimulation (ICS) for 10 min daily. In Experiment 2, only 2 intensities were offered. After stable daily rates of responding for each intensity of ICS were established, rats received either cocaine (5 or 10 mg/kg) or morphine (4 mg/kg) daily. Both cocaine and morphine significantly increased rates of responding. Naltrindole (NTI; 10 mg/kg) reduced rats' rates of responding under cocaine to those observed under vehicle. NTI had very little impact on morphine's effects. These data support the conclusion that selective 8 opioid receptor antagonists may be useful for treating cocaine addiction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)