Involvements of mu- and kappa-opioid receptors in morphine-induced antinociception in the nucleus accumbens of rats.
It is well known that there are three types of opioid receptors, mu- (MOR), delta- (DOR), and kappa-opioid receptor (KOR) in the central nervous system. The present study investigated the involvement of opioid receptors in morphine-induced antinociception in the nucleus accumbens (NAc) of rats. The hindpaw withdrawal latencies to thermal and mechanical stimulation increased markedly after intra-NAc administration of morphine. The antinociceptive effects induced by morphine were dose-dependently inhibited by intra-NAc administration of the non-selective opioid receptor antagonist naloxone. Furthermore, the morphine-induced antinociception was significantly attenuated by subsequent intra-NAc injection of the MOR antagonist beta-funaltrexamine or the KOR antagonist nor-binaltorphimine, but not the DOR antagonist naltrindole. The results indicate that MOR and KOR, but not DOR are involved in the morphine-induced antinociception in the NAc of rats.
Xiong
Wei
W
Laboratory of Neurobiology and The National Laboratory of Biomembrane and Membrane Biotechnology, College of Life Science, Peking University, Beijing 100871, China.
Yu
Long-Chuan
LC
D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D009714:Nucleus Accumbens / Q000187:drug effects* / Q000378:metabolism; D010146:Pain / Q000378:metabolism* / Q000503:physiopathology; D010812:Physical Stimulation; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time / Q000187:drug effects; D017465:Receptors, Opioid, delta / Q000037:antagonists & inhibitors; D017473:Receptors, Opioid, kappa / Q000037:antagonists & inhibitors / Q000502:physiology*; D017450:Receptors, Opioid, mu / Q000037:antagonists & inhibitors / Q000502:physiology*
D000701:Analgesics, Opioid; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D009270:Naloxone; C051844:norbinaltorphimine; D009271:Naltrexone; C024524:beta-funaltrexamine; D009020:Morphine; C055382:naltrindole