Blockade by naltrexone of analgesia produced by stimulation of the dorsal raphe nucleus.
Naloxone blockade of stimulation-produced analgesia in the rat is partial and variable. In the present study the effectiveness of the long-acting narcotic antagonist naltrexone is examined. Bipolar stainless steel electrodes were implanted in the dorsal raphe nucleus or ventral periaqueductal gray matter of male rats. Analgesia produced by electrical stimulation was tested by the tail flick method before and twenty min following the administration of saline or naltrexone. Saline administered IP failed to alter the analgesic response. Following naltrexone the degree of analgesia was reduced by a mean of 79% for IV injection (3.7 mg/kg) and by means of 26%, 52%, 81% and 83% for IP administration of 0.3, 1.0, 3.0 and 10 mg/kg, respectively. These results confirm the participation of opiate mechanisms in stimulation-produced analgesia, and indicate that, under certain circumstances, only opiate mechanisms are involved.
D000698:Analgesia; D000818:Animals; D001933:Brain Stem / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D008297:Male; D009270:Naloxone / Q000031:analogs & derivatives*; D009271:Naltrexone / Q000494:pharmacology*; D011903:Raphe Nuclei / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains
D009270:Naloxone; D009271:Naltrexone