Does naloxone suppress self-stimulation by decreasing reward or by increasing aversion?
Fifty-eight rats were implanted with electrodes in the ventrolateral midbrain central gray from which both self-stimulation reward and/or stimulation-produced analgesia can be obtained. Thirty-nine cases were positive for self-stimulation; of these, 24 also displayed significant stimulation-produced analgesia and 15 did not. Injections of the opiate receptor blocker, naloxone, suppressed self-stimulation by approximately 40% at both analgesic and non-analgesic reward sites. Since naloxone failed to act preferentially at analgesic reward sites, the hypothesis that naloxone suppresses self-stimulation primarily by antagonizing endorphin-mediated analgesia, and thereby increasing the aversive properties of the brain stimulation, was not supported. Rather, the data are consistent with the hypothesis that naloxone suppresses self-stimulation by antagonizing endorphin-mediated reward.
D000818:Animals; D003864:Depression, Chemical; D004298:Dopamine / Q000502:physiology; D008297:Male; D009270:Naloxone / Q000494:pharmacology*; D009638:Norepinephrine / Q000502:physiology; D010146:Pain / Q000503:physiopathology; D010487:Periaqueductal Gray / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D012653:Self Stimulation / Q000187:drug effects* / Q000502:physiology
D009270:Naloxone; D004298:Dopamine; D009638:Norepinephrine