Ethanol is a potent inhibitor of muscarinic receptor-mediated proliferation in glial cells. Glial proliferation has been suggested as a major target of ethanol neurotoxicity during development, leading to the microencephaly that is a predominant feature of fetal alcohol syndrome. As part of an attempt to understand the mechanism of ethanol's inhibitory effects on muscarinic receptor-mediated proliferation, this study investigated the effects of ethanol on the expression of the immediate-early genes (IEGs), c-fos and c-myc, whose induction is thought to be an essential first step in the initiation of the mitogenic program. Unexpectedly, ethanol had no inhibitory effect on c-fos and c-myc mRNA expression induced in primary rat cortical astrocytes by the mitogens carbachol, histamine, or tetradecanoyl phorbol 13-acetate; rather, a modest potentiation of IEG expression was observed in the presence of 25 to 100 mM ethanol. Control experiments showed that ethanol alone was capable of IEG mRNA induction, with 100 mM ethanol inducing IEG mRNA levels comparable with those induced by 100 ng/ml of tetradecanoyl phorbol 13-acetate; as measured by [3H]thymidine incorporation, however, 25 to 100 mM ethanol had no effect on proliferation. Experiments with the protein kinase C inhibitor bisindolylmaleimide and the Ca2+ chelators BAPTA and EGTA indicated that this IEG induction by ethanol was not mediated by protein kinase C or Ca2+. A possible explanation for this ethanol-induced IEG expression in the absence of a proliferative effect might be found in the increasing number of studies showing IEG involvement (especially that of c-myc) in apoptosis.