Expression of morphine-conditioned hyperactivity is attenuated by naloxone and pimozide.
The present experiments assessed whether morphine-conditioned hyperactivity could be attenuated by either the opiate antagonist naloxone or the dopamine antagonist pimozide. Both of these antagonists were shown to block the unconditioned hyperactivity induced by 2 mg/kg morphine (Experiment 1). Rats were then conditioned by pairing this dose of morphine repeatedly with a distinctive environment (Experiment 2). Following several drug-environment pairings, rats displayed a hyperactive conditioned response (CR) when exposed to the environment in the absence of the drug. CR expression was counteracted by 1 mg/kg naloxone and was attenuated by pimozide (0.25, 0.33, and 0.4 mg/kg) in a dose-related manner. These findings suggest that the unconditioned and conditioned hyperactive responses produced by morphine may involve similar neuropharmacologic substrates.
Neisewander
J L
JL
Department of Psychology, University of Kentucky, Lexington 40506.
Bardo
M T
MT
D000818:Animals; D003214:Conditioning, Classical / Q000187:drug effects*; D006948:Hyperkinesis / Q000139:chemically induced*; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology*; D010868:Pimozide / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D011954:Receptors, Dopamine / Q000378:metabolism; D011957:Receptors, Opioid / Q000378:metabolism
D011954:Receptors, Dopamine; D011957:Receptors, Opioid; D010868:Pimozide; D009270:Naloxone; D009020:Morphine