Distribution of tyrosine hydroxylase, dopamine-beta-hydroxylase and phenylethanolamine-N-methyltransferase activities in coronal sections of the rat lower brainstem.

The activities of the three major catecholamines synthesizing enzymes were determined on supernatants from microcubes dissected out from 500 microns thick coronal sections of the rat lower brainstem. The microcubes exhibiting significant or high enzymatic activities represented only one-third of the microcubes analyzed and were generally localized either in the dorso-medial or in the ventro-lateral region of the lower brainstem. In the ventro-lateral region, referred to as the A1-C1 region, the rostro-caudal distribution of the enzymatic activities exhibited a small difference between the maximal TH and DBH activities and the maximum PNMT activity located 500 microns more rostrally. Conversely, in the dorso-medial region, referred to as the A2-C2 region, there was a much larger rostro-caudal difference (about 1500 microns) between the peaks of TH and DBH activities and the more rostral peak of PNMT activity. Such a distribution suggests a separation between the adrenaline (A) and the noradrenaline (NA) containing neurons within the dorso-medial region. According to the results of this study, a preferential microdissection of the A versus NA neurons seems possible in the A2-C2 region of the rat medulla oblongata.