Increased tyrosine hydroxylase activity in central adrenaline neurons after reserpine treatment.

By using preferential microdissection of the adrenaline (A) and noradrenaline (NA) neurons within the A2-C2 region of the rat medulla oblongata, it was possible to study the biochemical response of these two neuronal populations to reserpine administration. Three days after reserpine injections (10 mg/kg s.c., per day for 3 days), tyrosine hydroxylase (TH) activity was increased in the adrenergic C2 region whilst no change was observed in the noradrenergic A2 region. The response of the A neurons to reserpine was of lesser magnitude than the increase in TH activity observed under the same conditions in the NA neurons of the locus coeruleus and of the A5 region, and was likely to have originated in the A cell bodies. In contrast with previous studies, this work suggests that the A-containing neurons are responsive to reserpine administration, despite the lack of change in phenylethanolamine-N-methyltransferase activity.