Imoaired thermal regulation in juvenile rats following perinatal methadone exposure

Offspring of female rats injected daily with methadone (5 mg/kg) or saline were cross-fostered at birth to form groups exposed to methadone during gestation (G), lactation (L), or gestation and lactation (G-L); controls (C) were exposed only to saline. Rectal temperature, body weight and food consumption were measured from postnatal Days 36-51. Ambient temperature was maintained at 21°C except for Days 42-45, when the temperature was 10°C. Group G rats never differed from controls, but offspring in Groups L and G-L were hypothermic at room temperature; Group G-L rats exhibited a further temperature loss during the cold stress. There were no group differences in food consumption after Day 39, and all groups increased food intake while in the cold. Group differences in body weight were not reliable but Group G-L rats gained less weight than the rest during the experiment, whereas Group L rats gained more. These results indicate that, depending upon treatment schedule, perinatal methadone exposure is associated with hypothermia during the postweaning period. A prolonged withdrawal reaction from methadone may account for the impaired thermal regulation.