The effect of environmental factors on morphine withdrawal in C57BL/6J mice: running wheel access and group housing

Abstract

There is evidence to suggest that the rewarding effects of drugs of abuse can be altered by environmental manipulations such as housing conditions and access to running wheels. There is less information about how these environmental manipulations alter withdrawal behaviors following the termination of chronic drug administration. The objective of this study is to examine the effects of access to running wheels and group housing on spontaneous morphine withdrawal. C57BL/6J mice were assigned to one of the three housing conditions: wheel access (singly housed), no wheels (singly housed), or group-housed (no wheels). Mice received 30 or 56 mg/kg morphine or saline (s.c.) twice daily for 5.5 days. At baseline and at 8, 24, 32, and 48 h following the final injection, latency to respond on a hot plate was determined across a range of temperatures (50, 52, 54, and 56 °C). Latency to respond decreased as a function of temperature. Response latencies during the withdrawal period were decreased in mice without wheel access treated with both 30 and 56 mg/kg of morphine. This increase in thermal sensitivity was significantly attenuated in singly housed mice with wheel access and in group-housed mice; however, the effects were less pronounced in the group-housed mice and depended upon the time during withdrawal. Both wheel access and group housing attenuate the increase in thermal sensitivity seen in morphine-treated mice during morphine withdrawal.