Social housing conditions influence morphine dependence and the extinction of morphine place preference in adolescent mice

Social environment alters opioid‐induced hyperalgesia and antinociceptive tolerance in adolescent mice

“…Similar to our previous studies as well as others (Kaplan et al., ; Bates et al., ), mice were injected once daily (9:00 a.m.) in their home cage for 6 (experiment 1) or 14 (experiment 2) consecutive days with 20 mg/kg of morphine sulphate (subcutaneously, Sigma‐Aldrich, St. Louis, MO, USA) or saline (10 ml/kg).…”

“…Similar to our previous studies (Hofford et al., ; Cole et al., ; Bates et al., ), mice were group‐housed four per cage. Morphine only (MOR) and saline only (SAL) mice are animals where all four mice in the cage received the same treatment, i.e.…”

“…It is important to determine the effects of opioids in doses that produce substantial levels of pain relief, specifically for severe pain where opioids are needed and used. The 20 mg/kg dose was selected based on our previous studies which demonstrated a social effect on other morphine‐induced behaviours using this dose (Bates et al., ) and because this dose is within a range that somewhat models levels of pain relief required for pain management in both mice and humans.…”

“…Similar to humans, environmental enrichment, isolation and social reward were demonstrated to variously influence opioid dependence and reward in rodents (Broseta et al., ; El Rawas et al., ; Kennedy et al., ). Likewise, our recent studies suggest that susceptibility to acquire opioid dependence and reward in adolescent rodents is dependent on the nature of social housing conditions (Cole et al., ; Bates et al., ). These studies demonstrate that morphine‐injected adolescent mice housed with drug‐naïve animals (i.e.…”

“…Specifically, morphine cage‐mates express less jumping behaviour during morphine withdrawal as compared to morphine only mice (Bates et al., ). Additionally, morphine cage‐mates acquired morphine conditioned place preference (CPP) more slowly and extinguished it more readily than morphine only mice (Cole et al., ; Bates et al., ). Therefore, these findings indicate that certain social environments can mitigate the development of morphine dependence and reward.…”