STUDIES ON RAT AND HUMAN THYMUS TO DEMONSTRATE IMMUNOREACTIVITY OF CALCITONIN-GENE-RELATED PEPTIDE, TYROSINE-HYDROXYLASE AND NEUROPEPTIDE-Y

The peptidergic and noradrenergic innervation of rat and human thymus was investigated by immunohistochemistry at the light and electron mic roscopical level (avidin-biotin-complex, sucrosephosphate-glyoxylic-ac id, and immunogold techniques). The distribution of noradrenergic neur al profiles, and positive immunoreactivity for calcitonin gene-related peptide (CGRP), tyrosine hydroxylase (TH) and neuropeptide Y (NPY) is described in female rats during ageing, and in human children. In the neonatal rat thymus, the arteries and septa are well supplied by fine varicose nerves. In older animals (2 wk-1 y) the number of septa and blood vessels increase and consequently also the innervation. No nerve s were found in the cortex. Apart from the innervation of the septal a reas, immunoreactivity for CGRP and TH was present in thymic cells. Ex cept for the young rats (neonatal-14 d), all rats showed CGRP positivi ty in subcapsular/perivascular epithelial cells (type 1 cells). All ra t thymuses also contained a few TH positive cells in the medulla, whic h could only be confirmed as epithelial cells (type 6 cells) in childr en. Type 1 cells in the human thymus were not CGRP positive, but as in the rat, there were similar TH positive cells in the medulla. It was concluded that in addition to nerves containing CGRP, noradrenaline or dopamine, epithelial cells also contain these transmitters. They coul d therefore act on different cells (compared with neural targets) in a paracrine manner.