Involvement of endogenous beta-endorphin in antinociception in the arcuate nucleus of hypothalamus in rats with inflammation.
Although exogenous administration of beta-endorphin to the arcuate nucleus of hypothalamus (ARC) had been shown to produce antinociception, the role of endogenous beta-endorphin of the ARC in nociceptive processing has not been studied directly. The aim of the present study was to investigate the effect of endogenous beta-endorphin in the ARC on nociception in rats with carrageenan-induced inflammation. The hindpaw withdrawal latency (HWL) to noxious thermal and mechanical stimulation was assessed by the hot-plate test and the Randall Selitto Test. Intra-ARC injection of naloxone had no significant influence on the HWL to thermal and mechanical stimulation in intact rats. The HWL decreased significantly after intra-ARC injection of 1 or 10 microg of naloxone in rats with inflammation, but not with 0.1 microg of naloxone. Furthermore, intra-ARC administration of the selective mu-opioid receptor antagonist beta-funaltrexamine (beta-FNA) decreased the nociceptive response latencies to both stimulation in a dose-dependent manner in rats with inflammation, while intra-ARC administration of the selective delta-opioid receptor antagonist naltrindole or the selective kappa-opioid receptor antagonist nor-binaltorphimine (nor-BNI) showed no influences on the nociceptive response latency. The antiserum against beta-endorphin, administered to the ARC, also dose-dependently reduced the HWL in rats with inflammation. The results indicate that endogenous beta-endorphin in the ARC plays an important role in the endogenous antinociceptive system in rats with inflammation, and that its effect is predominantly mediated by the mu-opioid receptor.
Sun
Yan-Gang
YG
Department of Physiology, College of Life Sciences, Peking University, Beijing 100871, People's Republic of China.
Lundeberg
Thomas
T
Yu
Long-Chuan
LC
D000700:Analgesics / Q000037:antagonists & inhibitors / Q000627:therapeutic use*; D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000187:drug effects* / Q000502:physiology; D007106:Immune Sera / Q000494:pharmacology; D007249:Inflammation / Q000139:chemically induced / Q000188:drug therapy*; D008297:Male; D009292:Narcotic Antagonists / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D017450:Receptors, Opioid, mu / Q000037:antagonists & inhibitors / Q000502:physiology; D001615:beta-Endorphin / Q000037:antagonists & inhibitors* / Q000502:physiology / Q000627:therapeutic use*
D000700:Analgesics; D007106:Immune Sera; D009292:Narcotic Antagonists; D017450:Receptors, Opioid, mu; D001615:beta-Endorphin