Ontogeny of innervation of rat and ovine fetal adrenals

The formation of adrenocortical zonation occurs in rats during late gestati on. Since adult cortical function is modulated by neural mediators, it is p ossible that the development of differentiated function is dependent on cor tical innervation. The goal of this study was to compare the pattern and ti ming of rodent and ovine adrenal innervation during late organogenesis by s taining with antibodies directed against the neuropeptides vasoactive intes tinal peptide (VIP), calcitonin gene-related peptide (CGRP) and neuropeptid e tyrosine (NPY) and the catecholamine biosynthetic enzyme, tyrosine hydrox ylase (TOH). Rat adrenals were collected from fetal days 17-21 (term=21 day s) and ovine adrenals from fetal days 101-136 (term=145 days). Adrenals wer e fixed, cryosectioned at 100 mu and immunostained using Cy3-conjugated sec ondary antibodies. In both species, staining of VIP, CGRP, NPY and TOH fibe rs was observed in the capsule and subcapsular layers of the cortex during gestation. In late gestation, VIP- and NPY-positive ganglions cells were ob served near the medulla extending processes toward the outer cortex; in ovi ne adrenals, fibers from ganglion cells appeared to surround nests of outer cortical (presumably, zona glomerulosa) cells. These data show that phenot ypically distinct neural elements appear at different stages of adrenocorti cal development. The presence of neural elements in contact with adrenal co rtical cells supports the possibility for neural control of adrenocortical development.