Opioid-receptor blockade reduces nose-poke self-stimulation derived from medial entorhinal cortex.
Rats were trained to nose-poke for intracranial self-stimulation (SS) with electrodes unilaterally implanted in the medial entorhinal cortex. The acute effects of naloxone (NX; 0.1-10 mg/kg, IP) on a continuous reinforcement schedule were determined. Reductions in the self-stimulation rates occurred only at moderate doses (median of individual changes = -36% at 1 and 5 mg/kg), whereas the high dose (10 mg/kg) was ineffective. None of the doses influenced operant behavior. These results are consistent with the hypothesis that endogenous opioid-opiate receptor mechanisms play a modulatory role in SS reward. Considering that NX was administered systemically the action of the drug on reinforcement levels may be mediated by a site distinct from the locus of stimulation.
D000818:Animals; D002540:Cerebral Cortex / Q000502:physiology*; D004558:Electric Stimulation; D008297:Male; D009270:Naloxone / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000502:physiology*; D012201:Reward; D012653:Self Stimulation
D011957:Receptors, Opioid; D009270:Naloxone