c-Fos expression by dopaminergic receptor activation in rat hippocampal neurons

While dopamine is likely to modulate hippocampal synaptic plasticity, there has been little information about how dopamine affects synaptic transmissi on in the hippocampus. The expression of IEGs including c-fos has been asso ciated with late phase LTP in the CA1 region of the hippocampus, The induct ion of c-fos by dopaminergic receptor activation in the rat hippocampus was investigated ba using semiquantitative RT-PCR and immunocytochemistry. The hippocampal slices which were not treated with dopamine showed little expr ession of c-fos mRNA. However, the induction of c-fos mRNA was detected as early as 5 min after dopamine treatment, peaked at 60 min, and remained ele vated 5 h after treatment. Temporal profiles of increases in c-fos mRNA by R(+)-SKF-38393 (50 muM) and forskolin (50 muM) were similar to that of dopa mine. An increase in [cAMP] was observed in dopamine-, SKF-, or forskolin-t reated hippocampal slices. By immunocytochemical studies, control hippocamp al cells showed little expression of c-Fos immunoreactivity. However, when cells were treated with dopamine, an increase in the expression of c-Fos im munoreactivity was observed after treatment for 2 h, The treatment of hippo campal neurons with R(+)-SKF-38393 (50 muM) or forskolin (50 muM) also indu ced a significant increase in c-Fos expression. These results indicate that the dopamine D1 receptor-mediated cAMP dependant pathway is associated wit h the expression of c-Fos in the hippocampal neurons. These data are consis tent with the possible role of endogenous dopamine on synaptic plasticity v ia the regulation of gene expression. Furthermore, these results imply that dopamine might control the process of memory storage in the hippocampus th rough gene expression.