Morphine-induced conditioned taste aversions in the LEW/N and F344/N rat strains.
Previous reports have shown that the LEW/N and F344/N inbred rat strains display a differential sensitivity to cocaine in a number of preparations, with the LEW/N rats displaying an increased sensitivity to both the reinforcing and aversive effects of cocaine (relative to the F344/N rats). Given that the LEW/N rats are also more sensitive to the reinforcing effects of morphine than the F344/N strain, the present experiment examined the ability of morphine to condition taste aversions in the LEW/N and F344/N strains to determine if the general sensitivity to cocaine generalizes to another drug of abuse. Specifically, on four conditioning trials, 35 LEW/N and 33 F344/N female rats were allowed access to a novel saccharin solution and then injected with varying doses of morphine (0, 10, 32 and 56 mg/kg). On intervening recovery days, subjects were allowed 20-min access to water. Following the fourth trial, a final aversion test was administered. The F344/N rats, but not the LEW/N rats, rapidly acquired morphine-induced taste aversions at all doses of morphine. Pharmacokinetic differences between the strains were also assessed. Specifically, 10 mg/kg morphine (or vehicle) was administered to subjects of both strains and plasma morphine levels were analyzed at 0.5, 2 and 4 h postinjection. No differences in plasma levels between the strains were observed. Unlike with cocaine, the LEW/N rats do not seem generally sensitive to morphine (relative to the F344/N rats). Rather, the differential sensitivity of the two strains to these compounds seems to be preparation dependent. Possible mechanisms underlying the differential sensitivity evident in the strains were discussed.
Lancellotti
D
D
Psychopharmacology Laboratory, Department of Psychology, American University, Washington, DC 20016, USA.
Bayer
B M
BM
Glowa
J R
JR
Houghtling
R A
RA
Riley
A L
AL
D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects*; D004326:Drinking / Q000187:drug effects; D005260:Female; D009020:Morphine / Q000097:blood / Q000494:pharmacology*; D009294:Narcotics / Q000097:blood / Q000494:pharmacology*; D051381:Rats; D011916:Rats, Inbred F344; D011917:Rats, Inbred Lew; D013649:Taste / Q000187:drug effects*
D009294:Narcotics; D009020:Morphine