Morphine-induced conditioned place preference in preweanling and adult rats.
The ability of morphine to support a conditioned place preference (CPP) in preweanling (18-22-day-old) and adult (70-90-day-old) rats was assessed. Prior to a 15-min compartment preference test, subjects received a saline-paired, 30-min exposure to a distinct compartment 2 h prior to receiving an injection of 1 or 5 mg/kg of morphine or saline, paired with a 30-min exposure to an alternate compartment for 4 consecutive days. Although overall activity levels differed substantially across age, preweanling and adult rats displayed similar patterns of activity during conditioning. Moreover, only adults exhibited a significant sex difference; females were more active than were males following an injection of 5 mg/kg of morphine. Both doses of morphine supported a comparable CPP in preweanlings and adults, and both ages exhibited relatively low activity levels while in the morphine-paired compartment. These similarities across age suggest that the CPP procedure may prove to be useful in elucidating the ontogeny of learning, memory, and stimulus selection in rats.
Randall
C K
CK
Department of Psychology, University of Kentucky, Lexington 40506-0044, USA.
Kraemer
P J
PJ
Bardo
M T
MT
D000818:Animals; D000833:Animals, Suckling; D003213:Conditioning, Psychological / Q000187:drug effects* / Q000502:physiology*; D005260:Female; D007858:Learning / Q000187:drug effects; D008297:Male; D008568:Memory / Q000187:drug effects; D009020:Morphine / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012201:Reward; D012727:Sex Characteristics
D009020:Morphine