Ethanol-induced activation of the hypothalamic-pituitary-adrenal axis in a mouse model for binge drinking: role of Ro15-4513-sensitive gamma aminobutyric acid receptors, tolerance, and relevance to humans.

A mouse model for binge drinking has been developed in this laboratory, and several aspects of this model have been characterized. Many of the immunosuppressive effects of ethanol (EtOH) in this model seem to be mediated by activation of the hypothalamic-pituitary-adrenal (HPA) axis and consequent increases in the concentration of glucocorticoids, catecholamines, and perhaps other immunosuppressive mediators. The purpose of the work described here is to examine three important issues regarding the EtOH-induced neuroendocrine response in this model: 1) Are Ro15-4513-sensitive gamma aminobutyric acid type A (GABA-A) receptors involved in activation of the HPA axis by EtOH? 2) Does daily administration of EtOH produce tolerance with regard to activation of the HPA axis or with regard to suppression of natural killer cell activity? 3) Is the HPA axis activated by similar blood EtOH concentrations in humans and in the mouse model? Ro15-4513, a partial inverse agonist of GABA-A receptors, did not affect EtOH-induced increases in blood corticosterone levels. This suggests that Ro15-4513-sensitive GABA-A receptors are not involved in EtOH-induced activation of the HPA axis and that inhibition of corticosterone production is not the mechanism by which Ro-15-4513 blocks EtOH-induced immunosuppression. To evaluate tolerance, mice were given a daily dose of EtOH (6.5 g/kg by gavage) or vehicle (water) for 10 days. Control groups received vehicle or EtOH only on the last day of the experiment. At the optimum time after EtOH administration serum corticosterone and splenic NK cell activity were measured. The results indicate no significant alterations in the response to EtOH of mice exposed to EtOH for 10 days compared to those exposed only once. To compare the HPA axis response of mice and humans, lower EtOH dosages than generally used in our model were administered to mice, and the corticosterone response was compared to published data for humans who had similar ranges of blood EtOH levels. The results suggest that humans and mice exhibit activation of the HPA axis only when blood EtOH levels exceed approximately 0.14%. Together these results further characterize a mouse model for binge drinking that seems to provide a reasonable representation of many aspects of binge drinking in humans.