Morphological survey of reserpine-induced tyrosine hydroxylase in brainstem dopaminergic, noradrenergic and adrenergic neurons with special referenceto their projection fibers

Reserpine administration causes a long lasting increase in the activity of tyrosine hydroxylase (TH), the rate limiting enzyme of catecholamine synthe sis. In the present study, using a sensitive immunocytochemical technique t o detect changes in TH-molecules at the cellular level, we analyzed the res erpine-induced changes in TH-immunoreactivity in central noradrenergic, adr energic and dopaminergic neurons and fibers. After multiple reserpine treat ment, the intensity of TH-immunostainings of cell bodies and proximal dendr ites increased in noradrenergic neurons in the locus coeruleus (A6) and med ulla oblongata (A1, A2, A4 and A5), and in brainstem adrenergic neurons (C1 , C2 and C3). In projection areas of noradrenergic neurons in the cerebellu m, basal ganglia and cerebral cortex, immunoreactive varicose fibers were t hickened and elongated. In the cerebral cortex, coiled fibers appeared para llel and vertical to the brain surface, corresponding to the established no radrenaline fiber projections. In contrast, midbrain dopaminergic neurons ( A9 and A10) did not show any detectable changes in immunoreactivity either in midbrain cell bodies or forebrain projecting fibers of the striatum and cingulate cortex. Thus, it is concluded that reserpine-administration induc ed TH molecules in noradrenergic and adrenergic cell bodies, fibers and ter minals without affecting those in dopaminergic neurons.