Temperature dependence of ethanol depression in rats.

The relationship between ambient temperature, body temperature, and brain sensitivity to ethanol was investigated in rats. Drug naive male Long Evans rats were injected IP with a hypnotic dose of ethanol (2.75 g/kg, 20% w/v). Immediately after injection, separate groups were exposed to one of five ambient temperatures from 12 to 34 degrees C. Ambient temperature significantly affected wake-up rectal temperature, sleep-time, and wake-up brain ethanol concentration. Sleep-times in individual rats increased 387% (from 24.0 min at 12 degrees C to 116.8 min at 34 degrees C) and wake-up brain ethanol concentrations decreased 79% (from 3.6 mg/g at 12 degrees C to 2.3 mg/g at 34 degrees C) as body temperatures increased from 35 to 41 degrees C. In addition, wake-up rectal temperatures were significantly, positively correlated with sleep-times (r = 0.32, P less than 0.05) and significantly, negatively correlated with wake-up brain ethanol concentrations (r = -0.49, P less than 0.01), further suggesting that brain sensitivity to ethanol increases as body temperature increases. These results are consistent with previous findings in mice, fit membrane perturbation theories of anesthesia, and indicate that temperature dependence of ethanol sensitivity is a general phenomenon extending across species. In conjunction with previous findings, the results also suggest that body temperature during intoxication may participate in mediating species differences in ethanol sensitivity.