Afferent regulation of neurotransmitter metabolism in perikarya and terminals of developing sympathetic neurons

Steady-state levels and turnover of the neurotransmitter, norepinephrine (NE), were measured in sympathetic perikarya and in two sympathetic target organs in the rat at various times during postnatal development. NE content in sympathetic perikarya in the superior cervical ganglion (SCG) increases 15-fold from birth to reach adult levels by 60 days. This increase in NE content parallels the increase in total protein in the ganglion. The rate of turnover of NE in the sympathetic perikarya increases slightly from birth to adulthood. Since the perikarya in the SCG project to a variety of different targets in the head and neck, NE metabolism was also examined in two terminal sympathetic plexuses, in the iris and in the submandibular gland (SMG). The terminal noradrenergic plexuses within these target organs do not mature with the same time course. In the iris, levels of NE increase 24-fold from birth until 90 days postnatally. Turnover of NE in sympathetic terminals in the iris at the time of birth is equivalent to that in the adult. In contrast, both the content and turnover of NE in sympathetic terminals in the SMG are very low at birth, and increase dramatically in the first month postnatally. Deafferentation of the SCG at birth impairs the development of normal levels of NE in sympathetic perikarya by approximately 40%, and total ganglionic protein is similarly affected. NE turnover in sympathetic perikarya deafferented at birth is only slight reduced from normal. The response to neonatal deafferentation differs in the two terminal sympathetic plexuses. In neurons that project to the iris, no detectable NE turnover could be measured, although the content of transmitter attains 64% of control values after deafferentation.(ABSTRACT TRUNCATED AT 250 WORDS)