Enhancement of morphine withdrawal signs in the rat after chronic treatment with naloxone.
Chronic treatment of rats with naloxone for 5 days increased the analgesic threshold (hot plate latency). Further, when rats were treated with morphine-admixed food for 3 days after the chronic naloxone treatment the withdrawal signs precipitated by naloxone were significantly greater in the naloxone-pretreated rats than in saline-pretreated rats. These results suggest that paradoxical analgesia and enhancement of the morphine withdrawal signs induced by chronic naloxone treatment may be associated mainly with up-regulation of mu- and delta-opioid binding sites in the central nervous system.
Suzuki
T
T
Department of Applied Pharmacology, School of Pharmacy, Hoshi University, Tokyo, Japan.
Fukagawa
Y
Y
Misawa
M
M
D000698:Analgesia; D000818:Animals; D001835:Body Weight / Q000187:drug effects; D008297:Male; D009021:Morphine Dependence / Q000503:physiopathology*; D009270:Naloxone / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000502:physiology; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu; D013375:Substance Withdrawal Syndrome / Q000503:physiopathology*; D015854:Up-Regulation / Q000502:physiology
D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu; D009270:Naloxone