The effects of lipopolysaccharide (LPS) and several cytokines or the c-fos and c-jun mRNA expression were examined in primary cultured astrocytes. Either LPS (500 ng/mL) or inter-feron-$gamma$ (IFN-$gamma$ 5 ng/mL) alone increased the level of c-fos mRNA (1 h). However, tumor necro-sis factor-$alpha$ (TNF-$alpha$; 10 ng/mL) or interleukin-4 (IL-1$eta$: 5 ng/mL) alone showed no significant induction of the level of c-fos mRNA. TNF-$alpha$ showed a potentiating effect in the regulation of LPS-induced c-fos mRNA expression, whereas LPS showed an inhibitory action against IFN-Y-induced c-fos mRNA expression. LPS, but not TNF-$alpha$, IL-1$eta$ and IFN-$gamma$, increased the level of c-jun mRNA (1 h). TNF-$alpha$ and IFN-$gamma$ showed an inhibitory action against LPS-induced c-jun mRNA expression. Both phorbol 12-myristate 13-acetate (PMA; 2.5 mM) and forskolin (FSK, 5 mM) increased the c-fos and c-jun mRNA expressions. In addition, the level of c-fos mRNA was expressed in an antagonistic manner when LPS was combined with PMA. When LPS was co-treated with either PMA or FSK, it showed an additive interaction for the induction of c-jun mRNA expression. Our results suggest that LPS and cytokines may be actively involved in the regulation of c-fos and c-jun mRNA expressions in primary cultured astrocytes. Moreover, both the PKA and PKC pathways may regulate the LPS-induced c-fos and c-jun mRNA expressions in different ways.