Whereas the immunosuppressive effects of chronic alcohol use have been well documented, little is known about the effect of ethanol on the neuroimmune response. We previously demonstrated that PRL is a potent mitogen and induces the expression of several inflammatory cytokines, including tumor necrosis factor-alpha (TNF alpha) in cultured rat astrocytes. The aim of this study was to examine the effects of ethanol on PRL-induced mitogenesis and TNF alpha expression in cultured rat astrocytes. We found that low concentrations of ethanol blocked PRL-induced increases in [3H]thymidine incorporation and TNF alpha levels. In contrast, ethanol had no effect on platelet-derived growth factor- or fibroblast growth factor-induced increases in [3H]thymidine incorporation. Radioligand binding analysis revealed that ethanol did not effect PRL receptor binding. We also examined the effect of prenatal alcohol exposure (PAE) on PRL-induced mitogenesis and cytokine expression. PAE during the last 5 days of gestation blunted the PRL-induced increase in [3H]thymidine incorporation and TNF alpha levels in cells grown in the absence of ethanol in the culture medium. Addition of ethanol to primary PAE astrocyte cultures resulted in a modest increase in basal [3H]thymidine incorporation, but completely blocked the PRL-induced increase in [3H]thymidine incorporation and TNF alpha levels. In contrast, platelet-derived growth factor- and serum (10%)-induced increases in [3H]thymidine incorporation remained intact. Together, these data indicate that ethanol blocks PRL-induced mitogenesis and the expression of TNF alpha in cultured rat astrocytes and are consistent with the possible inhibition of the astrocytic response by ethanol in vivo.