Ontogeny of ethanol-induced motor impairment following acute ethanol: Assessment via the negative geotaxis reflex in adolescent and adult rats

Adolescent rats have been observed to be less sensitive than adults to a number of ethanol effects that may serve as feedback cues to reduce further ethanol intake. Among these findings are a few reports of attenuated sensitivities of adolescents to ethanol-induced motor impairment. The purpose of the present study was to further explore potential age-related differences in ethanol-induced motor impairment in both male and female adolescent (postnatal day [P]28–32), and adult (P68–72) Sprague–Dawley rats using an inclined plane assessment of the negative geotaxis reflex. Adult males displayed significant motor impairment at 1.5 g/kg, whereas adolescent males required higher doses, showing significant motor impairment only at doses of 2.25 g/kg ethanol or greater. Intoxicated practice did not significantly influence level of motor impairment at either age. When female rats of both ages were separately analyzed in terms of their response to ethanol, a dose of 1.5 g/kg ethanol was found to significantly impair adults, whereas adolescent females showed significant motor impairment when challenged with 2.25 g/kg but not 1.5 g/kg ethanol. Yet when the 1.5 g/kg data of females at the two ages were directly compared, no significant age difference was seen at this dose. These data document an attenuated sensitivity of adolescent relative to adult rats to the motor impairing effects of ethanol using a stationary inclined plane test, an effect particularly robust in male animals, and demonstrates the utility of this test for assessment of motor coordination in adolescent and adult rats.