Quantitative analysis of tyrosine hydroxylase-, aromatic L-amino acid decarboxylase- or phenylethanolamine-N-methyltransferase-immunoreactive neuronsin the human medullary C1 region

Tyrosine hydroxylase (TH) is the first step and rate-limiting catecholamine -synthesizing enzyme. Recently, TH neurons lacking higher step catecholamin e-synthesizing enzyme(s) have been described in several regions of the huma n brain. The present study was conducted to examine whether such non-catech olaminergic TH neurons exist In the human medullary C1 adrenergic region. W e quantitatively analyzed neurons immunoreactive for TH, aromatic L-amino a cid decarboxylase (AADC) or phenylethanolamine-N-methyltransferase (PNMT) i n the C1 region of four autopsy cases (24-64 y. o., both sexes), ail withou t detectable neurological and psychiatric diseases. In all of the cases, th e numbers of TH-immunoreactive (-ir) neurons were largest. The numbers of A ADC-ir neurons were generally larger than those of PNMT-ir neurons. Double staining of TH and PNMT confirmed the existence of TH (+)/PNMT (+) neurons and TH (+)/PNMT (-) neurons. It is indicated that the human C1 adrenergic r egion contained noncatecholaminergic TH neurons, the significance of which remains to be elucidated.