Effects of naloxone on the self-stimulation behavior of the postero-lateral area of the hypothalamus in rats--influence of procedural conditions.

Rats exhibiting self-stimulation behavior through chronic electrodes implanted in the posterolateral part of the hypothalamus were subcutaneously injected with low doses (0.003-0.3 mg/kg) of naloxone. The animals were allowed to self-regulate the duration of rewarding brain stimulation. It was found that naloxone increases the duration of self-stimulation in rats in which the brain stimulation has previously been associated with footshock. Vehicle injections or injections of naloxone in rats that had not received footshock prior to testing, did not modify self-stimulation behavior. It is suggested that naloxone may facilitate an aversive central component of the brain stimulation; the conditioned rats therefore increased the duration of brain stimulation to compensate for this negative process.