Social influences on morphine sensitization in adolescent females

Abstract

We recently observed that social interactions influence morphine responsiveness in adolescent males. Given sex-related differences in both social interactions and responses to morphine, the present study examines social influences on morphine sensitization in adolescent female mice. Four experimental groups were examined: (1) morphine-treated mice (twice daily, 10-40 mg/kg, s.c.) housed physically and visually separated from saline-treated mice ('morphine only'), (2) morphine-treated mice housed together with saline-treated mice ('morphine cage-mates (of saline)'), (3) saline-treated mice housed together with morphine-treated mice ('saline cage-mates (of morphine)'), and (4) saline-treated mice housed physically and visually separated from morphine-treated mice ('saline only'). Following the treatment period, mice were tested individually for their locomotor response to 20 mg/kg morphine (s.c.). There were no significant differences in morphine-induced hyper-locomotion between saline only and saline cage-mates (of morphine) female adolescent mice. Notably, morphine only mice exhibited significantly greater morphine sensitization as compared to morphine cage-mates (of saline). Thus, this study demonstrates social influences on morphine sensitization in adolescent females. Drug use during early adolescence is a key predictor of later drug abuse and dependence during adulthood. Thus, understanding the specific vulnerabilities to drug use in this age group may represent a first step in helping develop more effective treatment programs.

Fig. 1. Morphine locomotor sensitization in adolescent female mice

(A) Total distance traveled (cm) in the 60 minutes prior to morphine administration (Baseline, White bars) and in the 60 minutes following 10 mg/kg morphine injection (Morphine, Gray bars). (§) indicates a significant difference from baseline (p<0.001); (*) indicates a significant difference from saline only mice (p<0.01); (b) indicates a significant difference between the morphine cage-mates (of saline) and morphine only mice (p<0.01). (B) Total distance traveled (cm) during the entire 120 minute test, segmented into 5 minute intervals. Arrow indicates time of morphine administration. (*) indicates a significant difference from saline only mice (p<0.05); (#) indicates a significant difference from saline only mice (p<0.001); (a) indicates a significant difference between the morphine cage-mates (of saline) and morphine only mice (p<0.05); (b) indicates a significant difference between the morphine cage-mates (of saline) and morphine only mice (p<0.01); (c) indicates a significant difference between the morphine cage-mates (of saline) and morphine only mice (p<0.001). Results are presented as mean ± SEM.