NEURONAL MARKERS, PEPTIDES AND ENZYMES IN NERVES AND CHROMAFFIN CELLSIN THE RAT ADRENAL-MEDULLA DURING POSTNATAL-DEVELOPMENT

Neuronal markers, peptides and enzymes were analyzed in the rat adrena l medulla during the postnatal period, i.e., when the 'functional' spl anchnic innervation is assumed to 'mature'. Nerve fibers were present on day 2 as indicated by neurofilament 10 (NF10)- and growth associate d protein 43 (GAP43)-like immunoreactivities (LIs). Acetylcholinestera se (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. Th us, the presumably sensory innervation of the adrenal gland seems to p recede the development of the autonomic nerves. The AChE- and ENK-IR f ibers may exert a suppresive effect on ENK-, CGRP- and neurotensin (NT )-LIs in chromaffin cells, since the levels of these peptides were hig h 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 ex pressed in many chromaffin cells at all stages and its turnover rate s eemed to decrease towards the adult stage. The expression of the catec holamine synthezising enzymes changed only marginally during developme nt. These results indicate that the preganglionic fibers, but not the sensory axons, in the splanchnic nerve are involved in the development al control of expression of some, but not all, peptides in the chromaf fin cells and that these changes thus may reflect the maturation of a 'functional' transmission.