Ethylketocyclazocine and bremazocine analgesia in neonatal rats.
In three experiments we examined the analgesic potency of kappa opioid receptor agonists in 2- and 16-day-old rats. Ethylketocyclazocine (1-50 mg/kg) produced similar dose- and time-dependent increases in the latency to retract a hind paw from a noxious thermal stimulus in rats of both ages. Bremazocine (0.001-10 mg/kg), a kappa agonist with reported antagonist activity at mu receptors, was also effective in producing analgesia in 2-day-old rats. The dose-effect relationship for bremazocine was nonmonotonic. Bremazocine analgesia (0.1 mg/kg) was reversed by both naltrexone and MR2266, a putative kappa opioid antagonist. These results are discussed in terms of the functional integrity of a kappa analgesic system in the developing rat.
Helmstetter
F J
FJ
Department of Psychology, Dartmouth College, Hanover, NH 03755.
Calcagnetti
D J
DJ
Cramer
C P
CP
Fanselow
M S
MS
D000698:Analgesia; D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D000831:Animals, Newborn; D001575:Benzomorphans / Q000494:pharmacology*; D003496:Cyclazocine / Q000031:analogs & derivatives* / Q000494:pharmacology; D016314:Ethylketocyclazocine; D005260:Female; D008297:Male; D009019:Morphinans / Q000494:pharmacology*; D009271:Naltrexone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D051381:Rats
D000700:Analgesics; D001575:Benzomorphans; D009019:Morphinans; D009292:Narcotic Antagonists; C027247:MR 2266; D016314:Ethylketocyclazocine; D009271:Naltrexone; C027248:bremazocine; D003496:Cyclazocine