Cellular localization of tyrosine hydroxylase mRNA and its regulation in the rat adrenal medulla and brain by in situ hybridization with an oligodeoxyribonucleotide probe.

Tyrosine hydroxylase (TH) is the rate-limiting enzyme in the synthesis of catecholamines in neural tissues and adrenal medulla. To study the expression of the TH gene and its regulation in adult and developing neural tissues, we have synthesized an oligodeoxyribonucleotide probe (oligomer) that is specific for TH mRNA. Using Northern blot hybridization of polyadenylated RNAs from adrenal gland, brain stem, liver, and cerebral cortex with the 32P-labeled oligomer, a single TH mRNA of 1.9 kb was detected in adrenal gland and brain stem but not in liver and cerebral cortex. Using this TH-specific oligomer, TH mRNAs were localized to the chromaffin cells in the adrenal medulla and to catecholaminergic neurons in locus coeruleus and substantia nigra by in situ hybridization histochemistry. After reserpine administration, the intensity of hybridization signal was increased to threefold that of normal in sections of adrenal medulla and twofold that of normal in locus ceruleus. No difference in hybridization signal intensity was observed in the substantia nigra of normal and reserpine-treated animals. Use of this specific TH probe in in situ hybridization procedures represents a powerful approach to the study of regulation of TH gene expression at the cellular level.