Reductions in locomotor activity following central opioid receptor subtype antagonists in rats.
Opioid agonists produce biphasic (decreases then increases) effects upon activity in rats. General opioid antagonists typically suppress activity. Selective opioid antagonists reduce weight and food intake. However, the latter effects cannot fully account for the former effects. To assess the possibility that selective opioid antagonists might decrease weight by increasing activity, the present study examined whether central administration of either mu (beta-funaltrexamine: 20 micrograms), mu1 (naloxonazine: 50 micrograms), delta1 ([D-Ala2,Leu5,Cys6]enkephalin: 40 micrograms), delta2 (naltrindole isothiocyanate: 20 micrograms), or kappa1 (nor-binaltorphamine: 20 micrograms) opioid antagonists altered total, ambulatory, or stereotypic activity. Each of the antagonists significantly reduced total (mu: 18%, mu1: 31%, delta1: 42%, delta2: 37%, kappa1: 31%), ambulatory (mu: 17%, mu1: 27%, delta1: 34%, delta2: 37%, kappa1: 31%), and stereotypic (mu: 19%, mu1: 34%, delta1: 49%, delta2: 37%, kappa1: 31%) activity on the first day. All three activity measures were reduced by delta1 and delta2 antagonism on the second day, whereas mu antagonism reduced total and stereotypic activity on the second day. The activity reductions induced by selective opioid receptor subtype antagonists parallel effects induced by general opioid antagonism, and suggest that antagonist-induced weight loss effects independent of intake reductions are not due to antagonist-induced hyperactivity.
Leventhal
L
L
Neuropsychology Doctoral SubProgram, Queens College, City University of New York, Flushing 11367, USA.
Cole
J L
JL
Bodnar
R J
RJ
D000818:Animals; D004745:Enkephalins / Q000494:pharmacology*; D008124:Locomotion / Q000187:drug effects*; D008297:Male; D009270:Naloxone / Q000031:analogs & derivatives* / Q000494:pharmacology; D009271:Naltrexone / Q000031:analogs & derivatives* / Q000494:pharmacology; D009292:Narcotic Antagonists; D051381:Rats; D017207:Rats, Sprague-Dawley
D004745:Enkephalins; D009292:Narcotic Antagonists; D009270:Naloxone; D009271:Naltrexone; C024524:beta-funaltrexamine; C034643:naloxonazine