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


OBJECTIVE
The objective of this study is to examine the effects of access to running wheels and group housing on spontaneous morphine withdrawal.


METHODS
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).


RESULTS
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.


CONCLUSIONS
Both wheel access and group housing attenuate the increase in thermal sensitivity seen in morphine-treated mice during morphine withdrawal.
Neurobiology Curriculum, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA. rebecca.balter@gmail.com
Rebecca E
RE
Balter
Linda A
LA
Dykstra
D000818:Animals; D004305:Dose-Response Relationship, Drug; D006358:Hot Temperature; D006799:Housing, Animal; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009020:Morphine / Q000008:administration & dosage / Q000009:adverse effects; D009021:Morphine Dependence / Q000503:physiopathology*; D012201:Reward; D012420:Running / Q000502:physiology*; D013375:Substance Withdrawal Syndrome / Q000534:rehabilitation*; D013696:Temperature; D013997:Time Factors
D009020:Morphine