title: Influence of inheritance and fostering on sensitivity to effects of morphine on nociception and locomotor activity in two inbred rat strains.
abstract: There are differences between individuals in their pain threshold, locomotor activity, and sensitivity to drugs of abuse which affect these processes. We have investigated the role of genetic differences and fostering in determining sensitivity to the action of morphine on nociception and locomotor activity in two strains of rats [Fischer-344 (F) and WAG/G (W)], using methods of reciprocal cross and cross-fostering. Nine-week old rats were used in the experiments. It was found that FF rats were more sensitive to the action of morphine on locomotor activity in open field apparatus than WW rats. Both types of F1 hybrids inherited a low sensitivity to the depressive action of morphine, their activity significantly differed from FF activity and had no distinction from that of WW rats. However, there was a strong maternal effect: if WW rats were fostered by a FF mother, the depression of their locomotor activity was similar to that of FF inbred rats, and vice versa. There were significant differences between normal and cross-fostered rats in all groups. WW rats had a higher sensitivity to thermal stimuli than FF rats. Both types of hybrids had intermediate nociceptive latencies. The strain difference between WW and FF rats in the baseline latencies of tail withdrawal disappeared after crossfostering-the latencies in FF rats were significantly decreased. Administration of morphine produced greater antinociception in FF rats than in WW. Cross-fostering of FF rats by WW mothers dramatically decreased their sensitivity to the analgesic action of morphine, while WW rats fostered by FF mothers did not change their resistance to morphine induced antinociception. Thus, the sensitivity of young rats to morphine-induced analgesia or depression of locomotor activity is mostly determined by fostering during the first 21 days.
authors.affiliation: Laboratory of Neurobiology of Cravings, State Addiction Research Center, Moscow, Russia.
authors.forename: S K
authors.initials: SK
authors.lastname: Sudakov
authors.forename: E V
authors.initials: EV
authors.lastname: Borisova
authors.forename: Y V
authors.initials: YV
authors.lastname: Lyupina
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D005260:Female; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009043:Motor Activity / Q000187:drug effects* / Q000502:physiology*; D009619:Nociceptors / Q000187:drug effects* / Q000502:physiology*; D010147:Pain Measurement / Q000187:drug effects; D051381:Rats; D011916:Rats, Inbred F344
chemical_list: D000701:Analgesics, Opioid; D009020:Morphine