COEXPRESSION OF DOPAMINE TRANSPORTER MESSENGER-RNA AND TYROSINE-HYDROXYLASE MESSENGER-RNA IN VENTRAL MESENCEPHALIC NEURONS

Radioactive in situ hybridization was used to map the cellular localization of dopamine (DA) transporter mRNA-containing cells in the adult rat central nervous system. The distribution of DA transporter mRNA-containing cells was compared to adjacent sections processed to visualize tyrosine hydroxylase (TH) mRNA, a marker of catecholamine containing neurones. TH mRNA-containing cells, visualized using an alkaline phosphatase labelled probe, were detected in the hypothalamus, midbrain and pons; the strongest hybridization signals being detected in the substantia nigra, ventral tegmental area and locus coeruleus. The distribution of DA transporter mRNA-containing cells was more restricted; a strong signal being detected in the substantia nigra pars compacta and ventral tegmental area only. No hybridization signal was detected in the locus coeruleus. By simultaneously hybridizing mesencephalic tissue with both the alkaline phosphatase-labelled TH probe and the S-35-labelled DA transporter probe we were able to demonstrate that both DA transporter and TH mRNAs are expressed by the same cells in the substantia nigra and ventral tegmental area. The restricted anatomical localization of DA transporter mRNA-containing cells and the lack of expression in the locus coeruleus and other adrenergic and noradrenergic cell groups confirms the DA transporter as a presynaptic marker of DA containing nerve cells in the rat brain.