Effects of an infusion of morphine into the accumbens nucleus upon acquisition of hypoalgesic and fear responses in rats exposed to a heart stressor.
Four experiments examined the effects of an infusion of morphine into the accumbens nucleus upon the aversive conditioning that can occur in rats exposed to the heated floor of a hot-plate apparatus. An infusion of morphine into the accumbens nucleus but not into the caudoputamen or into the prefrontal cortex impaired the acquisition of a conditioned hypoalgesic (Experiment 1) and fear (Experiment 4) response. This impairment was dose-dependent (Experiment 2) and mediated by opioid receptors in the accumbens nucleus, because it was removed by a systemic (Experiment 3a) or by an accumbal (Experiment 3b) infusion of naloxone. The results were attributed to an antagonism between the reinforcement process for aversive conditioning and the appetitive properties of an accumbal infusion of morphine.
Westbrook
R F
RF
School of Psychology, University of New South Wales, Kensington, Australia.
Harris
J A
JA
Good
A J
AJ
Paxinos
G
G
D000698:Analgesia; D000818:Animals; D001522:Behavior, Animal; D002421:Caudate Nucleus / Q000187:drug effects / Q000502:physiology; D003214:Conditioning, Classical / Q000187:drug effects* / Q000502:physiology; D005239:Fear / Q000187:drug effects*; D006358:Hot Temperature; D008297:Male; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D009714:Nucleus Accumbens / Q000187:drug effects* / Q000502:physiology; D011699:Putamen / Q000187:drug effects / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D012107:Research Design
D009020:Morphine