Neuronal markers, peptides and enzymes in nerves and chromaffin cells in the rat adrenal medulla during postnatal development

Neuronal markers, peptides and enzymes were analyzed in the rat adrenal medulla during the postnatal period, i.e., when the ‘functional’ splanchnic innervation is assumed to ‘mature’. Nerve fibers were present on day 2 as indicated by neurofilament 10 (NF10)- and growth associated protein 43 (GAP43)-like immunoreactivities (LIs). Acetylcholinesterase (AChE)- and enkephalin (ENK)-immunoreactive (IR) fibers, presumably of preganglionic nature, increased in number and intensity during the postnatal period. In contrast, calcitonin gene-related peptide (CGRP)- and galanin (GAL)-IR fibers were almost fully developed on day 2. Thus, the presumably sensory innervation of the adrenal gland seems to precede the development of the autonomic nerves. The AChE- and ENK-IR fibers may exert a suppresive effect on ENK-, CGRP- and neurotensin (NT)-LIs in chromaffin cells, since the levels of these peptides were high in the early postnatal period and then decreased. On the other hand, GAL-LI in chromaffin cells was low also in young rats, while GAP43-IR cells were observed at all stages. Neuropeptide tyrosine (NPY) was expressed in many chromaffin cells at all stages and its turnover rate seemed to decrease towards the adult stage. The expression of the catecholamine synthezising enzymes changed only marginally during development. These results indicate that the preganglionic fibers, but not the sensory axons, in the splanchnic nerve are involved in the developmental control of expression of some, but not all, peptides in the chromaffin cells and that these changes thus may reflect the maturation of a ‘functional’ transmission.