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

Abstract

The activities of the three major catecholamines synthesizing enzymes were determined on supernatants from microcubes dissected out from 500 μm 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 A 1-C 1 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 μm more rostrally. Conversely, in the dorso-medoal region, referred to as the A 2-C 2 region, there was a much larger rostro-caudal difference (about 1500 μm) 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 A 2–C 2 region of the rat medulla oblongata.