Autonomic responses to ethanol in adolescent and adult rats: a dose-response analysis.

Although the exact cause of the increase in ethanol consumption during adolescence is not known, age differences in sensitivity to some of ethanol's effects may play a contributory role. Prior research has shown little difference in the expression of ethanol-induced tachycardia between adolescents and adults following ethanol inhalation. In contrast, there is mounting evidence of ontogenetic differences in ethanol-induced hypothermia, although the nature of the ontogenetic effect observed has been found to vary across studies and even within labs. Relative ontogenetic differences in body temperature (BT) after ethanol administration appear to be driven in part by the amount of experimental perturbation associated with the test protocol, although differing ethanol exposure levels across studies may also have contributed to the variations in ontogenetic patterns that have been observed. To explore the latter possibility, the present study assessed ethanol-induced hypothermia and tachycardia in adolescent and adult male Sprague-Dawley rats examined in their home cages in the presence of their housing partner following intraperitoneal administration of 0.5, 1.5, or 3.0 g/kg ethanol. The results showed that, although adolescents did not show an adult-typical tachycardic effect at any dose, they proved more sensitive than adults to ethanol's hypothermic effects at the two highest doses. These findings suggest that not only the degree of experimental perturbation, but also the amount of ethanol exposure may differentially effect expression of age differences in ethanol-induced hypothermia, with adolescents showing greater hypothermia than adults at higher doses. Together with previous findings, these data contribute to the emerging picture that age differences in autonomic effects of ethanol appear to be particularly sensitive to dosing parameters and experimental protocols, unlike the generally more consistent ontogenetic findings observed across studies when using behavioral measures of ethanol sensitivity.