PARALLEL UP-REGULATION OF CATECHOLAMINE-SYNTHESIZING ENZYMES IN RAT-BRAIN AND ADRENAL-GLAND - EFFECTS OF RESERPINE AND CORRELATION WITH IMMEDIATE EARLY GENE-EXPRESSION

Changes in the mRNA levels of all catecholamine-synthesizing enzymes were examined 24 h after a single injection of reserpine by in situ hybridization. The responses of the midbrain dopaminergic cells in the ventral tegmental area and substantia nigra compacta, locus ceruleus and adrenal gland were studied in three groups of animals receiving either no injection, vehicle injection or reserpine 10 mg/kg subcutaneously. Increases in enzyme message signal observed by in situ hybridization were corroborated by Northern blot analysis for all four enzyme mRNAs isolated from the adrenal gland in these same three treatment groups. Differential increases of those enzyme mRNAs species expressed in the locus ceruleus and adrenal gland were found while no change of enzyme message was detected the midbrain. Two distinct subpopulations of adrenomedullary cells could be distinguished by their baseline levels of enzyme mRNA expression: the majority of medullary cells have moderate levels of all four enzyme mRNAs but a minority of cells show very high signal for the first three enzymes of the catecholamine synthesis pathway. To test whether reserpine elicits a selective transcriptional response of the catecholamine enzyme genes or induces other neuronal genes, cDNA probes for the growth-associated protein GAP-43 which is highly expressed and neurofilament L which is weakly expressed in monoaminergic neurons were used as independent cellular markers and showed no change in message levels. Changes in mRNA levels of the proto-oncogenes c-fos and c-jun were examined 1 h after injection of reserpine by in situ hybridization and compared to the pattern observed for the Fos protein immunohistochemically. C-fos and c-jun proto-oncogene activation was observed 1 h after reserpine in the locus ceruleus and adrenal medulla, specifically in those catecholaminergic structures that respond with increased enzyme gene transcription; in contrast, the dopaminergic neurons of the substantia nigra did not exhibit detectable proto-oncogene activation, only a small group of neurons in the ventral tegmental area showed c-fos without concomitant c-jun expression after reserpine.