Quantitative Analysis of Tyrosine Hydroxylase-, Aromatic L-Amino Acid Decarboxylase- or Phenylethanolamine-N-Methyltransferase-Immunoreactive Neurons in the Human Medullary C1 Region.

Tyrosine hydroxylase(TH) is the first step and rate−limiting catecholamine−synthesizing enzyme. Recently, TH neurons lacking higher step catecholamine−synthesizing enzyme(s) have been described in several regions of the human brain. The present study was conducted to examine whether such non−catecholaminergic TH neurons exist in the human medullary C1 adrenergic region. We quantitatively analyzed neurons immunoreactive for TH, aromatic L−amino acid decarboxylase(AADC) or phenylethanolamine−N−methyltransferase(PNMT) in the C1 region of four autopsy cases(24−64 y.o., both sexes), all without detectable neurological and psychiatric diseases. In all of the cases, the numbers of TH−immunoreactive(−ir) neurons were largest. The numbers of AADC−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 region contained non−catecholaminergic TH neurons, the significance of which remains to be elucidated.