Role of repeated exposure to morphine in determining its affective properties: place and taste conditioning studies in rats.
Male Sprague Dawley rats were injected daily with saline (morphine naive rats) or 20 mg/kg morphine (morphine experienced rats), starting at least 12 days before training. Subsequent place and taste conditioning indicated that 2.5 mg/kg morphine caused a significant increase in the amount of time spent on the least preferred side by morphine experienced but not by morphine naive rats; furthermore, saccharin consumption was markedly decreased and slightly increased by 10-20 mg/kg morphine in naive and experienced rats, respectively. It was concluded that morphine experience enhances the reinforcing efficacy of morphine and broadens the conditions under which the drug is reinforcing; thus it possibly increases morphine abuse potential.
Gaiardi
M
M
Institute of Pharmacology, University of Bologna, Italy.
Bartoletti
M
M
Bacchi
A
A
Gubellini
C
C
Costa
M
M
Babbini
M
M
D000818:Animals; D003216:Conditioning, Operant / Q000187:drug effects*; D004644:Emotions / Q000187:drug effects*; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D012439:Saccharin / Q000494:pharmacology; D013649:Taste / Q000187:drug effects*
D009020:Morphine; D012439:Saccharin