Changes in the muscarinic cholinergic receptors in the hippocampus of rats exposed to ethyl alcohol during the brain growth spurt.

Rats were exposed to ethanol from postnatal day 4 to day 10, using an artificial rearing procedure. One group received ethanol administered by a cyclic regimen, which resulted in high peak blood ethanol concentrations (BACs). Another group received the same daily dose of ethanol using a regimen which resulted in stable, moderate BACs. Two control groups consisted of rats reared artificially but not exposed to alcohol and rats reared normally by dams. All rats were raised to adulthood. Approximately half the rats were tested for behavioral activity levels and then sacrificed in order to assay the hippocampus for levels of cyclic GMP and protein after incubation with bethanechol (a muscarinic cholinergic agonist). The remaining rats were sacrificed and their hippocampi were assayed for muscarinic cholinergic receptors and protein content. Exposure to cyclic BACs with high peaks but not exposure to stable moderate BACs resulted in greater behavioral activity levels in both sexes and also a greater cyclic GMP responsiveness to a muscarinic cholinergic agonist. Furthermore, exposure to cyclic BACs with high peaks resulted in a significantly larger dissociation constant and a greater number of muscarinic cholinergic receptors. There were no differences among groups or sexes in protein content of the hippocampus. There were no interactions of the alcohol treatment with sex. Thus, in adult rats, exposure to alcohol during the brain growth spurt results in an increase in the dissociation constant and number of muscarinic cholinergic receptors in the hippocampus.