title: Mu opioid receptor agonist DAMGO-induced suppression of saccharin intake in Lewis and Fischer rats.
abstract: Rats suppress intake of a saccharin cue when paired with a drug of abuse such as morphine or cocaine. Relative to Lewis rats, Fischer rats exhibit greater avoidance of a saccharin cue following saccharin-morphine pairings. The present study used the mu agonist, [D-Ala2,N-MePhe4,Gly-ol5]enkephalin (DAMGO), to test whether strain differences in sensitivity of the mu receptor contribute to this effect. Water-deprived Lewis and Fischer rats were given 5 min access to 0.15% saccharin followed by an icv injection of either DAMGO (0.5 microg/1 microl/rat) or an equal volume of saline. There were six taste-drug pairings occurring at 48 h intervals. The results showed that, relative to the saline treated controls, all rats reduced intake of the saccharin cue following saccharin-DAMGO pairings. No differences occurred between strains. These data suggest that greater morphine-induced suppression of saccharin intake by the Fischer rats is not likely mediated by differences in sensitivity of the mu receptor. Other mechanisms are implicated.
authors.affiliation: Department of Neural and Behavioral Sciences, H181, Pennsylvania State University College of Medicine, 500 University Drive, Hershey, PA 17033, USA. chliu@psu.edu
authors.forename: Chuang
authors.initials: C
authors.lastname: Liu
authors.forename: Patricia
authors.initials: P
authors.lastname: Sue Grigson
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001245:Association Learning / Q000187:drug effects*; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology*; D005247:Feeding Behavior / Q000187:drug effects*; D008297:Male; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D051381:Rats; D011916:Rats, Inbred F344; D011917:Rats, Inbred Lew; D017450:Receptors, Opioid, mu / Q000819:agonists*; D012054:Reinforcement, Psychology; D012439:Saccharin; D013045:Species Specificity
chemical_list: D018377:Neurotransmitter Agents; D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D012439:Saccharin