INTRAREGIONAL VARIATION IN EXPRESSION OF SEROTONIN TRANSPORTER MESSENGER-RNA BY 5-HYDROXYTRYPTAMINE NEURONS

The distribution of the messenger RNA encoding the 5-hydroxytryptamine transporter was investigated in rat brain. 5-Hydroxytryptamine transp orter messenger RNA was found exclusively in the B1-B9 cell groups con taining the cell bodies of 5-hydroxytryptamine neurons. Combined in si tu hybridization and 5-hydroxytryptamine immunocytochemistry demonstra ted 5-hydroxytryptamine transporter gene expression in the majority of and exclusively in 5-hydroxytryptamine neurons. Cells differed in the ir levels of expression of 5-hydroxytryptamine transporter messenger R NA and 5-hydroxytryptamine immunofluorescence, but with a tight correl ation between the two parameters. Image analysis of cells from B7, the dorsal raphe nucleus, and B8, the median raphe nucleus, revealed sign ificant differences between groups in the mean cellular level of 5-hyd roxytryptamine transporter gene expression. Cells in the ventromedial subdivision of B7 displayed higher levels of expression than cells in B8 or cells in the lateral wings of B7. There was also heterogeneity i n the distribution of the cellular levels of expression for two other genes expressed by 5-hydroxytryptamine neurons: 1-aromatic amino acid decarboxylase messenger RNA and tryptophan hydroxylase messenger RNA. However, the relative levels of expression of these two genes within t he four regions studied differed from that of 5-hydroxytryptamine tran sporter messenger RNA. These results indicate intraregional difference s between 5-hydroxytryptamine neurons with respect to 5-hydroxytryptam ine transporter messenger RNA levels. Such differences may account for the differential sensitivity of 5-hydroxytryptamine neurons to cytoto xins. (C) 1998 IBRO. Published by Elsevier Science Ltd.