Changes in tyrosine hydroxylase and dopamine-beta-hydroxylase activities but not in phenylethanolamine-N-methyltransferase activity within central adrenaline neurons after 6-hydroxydopamine administration.

By using a new microdissection procedure allowing the noradrenaline (NA) and adrenaline (A) cell groups of the A2-C2 region to be sampled preferentially, it was possible to study the biochemical response of these two neuronal populations after 6-hydroxydopamine (6-OHDA) administration. Five days after an intraventricular 6-OHDA injection, tyrosine hydroxylase (TH) activity increased (+104%, P less than 0.01) in the adrenergic C2 region, in the locus coeruleus (LC) and in the A1-C1 region, while the NA A2 region exhibited no significant increase. Twenty-one days after 6-OHDA administration, dopamine-beta-hydroxylase (DBH) activity had decreased in both the noradrenergic regions (LC, A1-C1 and A2 regions) and in the C2 adrenergic region. Conversely, phenylethanolamine-N-methyltransferase (PNMT) activity was not modified either in the cell bodies or in the terminals located in the tractus intermediolateralis of the spinal cord and in the hypothalamic nuclei. These data suggest: (i) that adrenaline-containing neurons could be sensitive to the neurotoxic action of 6-OHDA since they exhibit changes in TH and DBH activities; and (ii) that the determination of PNMT activity may not be sensitive enough to estimate the functional integrity of the A cell bodies or terminals.