Postnatal development of adrenergic innervation in the tibial and vagus nerves of Fischer-344 rats.

Adrenergic innervation of rat tibial and vagus nerves was studied in male Fischer-344 rats between 1 and 84 days of age, using sucrose-phosphate-glyoxylic acid (SPG) histochemistry and the formaldehyde-induced fluorescence (FIF) method. Adrenergic nerve fibers were found in epi-perineurial blood vessels of the vagus nerve at one day of age, whereas blood vessels in the tibial nerve received the first adrenergic nerve fibers at 3 days. A few adrenergic nerve fibers were seen in the endoneurium of both tibial and vagus nerves at 7 days. The densities of adrenergic innervation increased gradually during the first 4 postnatal weeks, and at 21 days the distributions of adrenergic innervation in both nerves resembled those in adult animals. The results suggest that development of adult adrenergic innervation in rat peripheral nerves occurs during the first postnatal month and that sympathetic innervation becomes available to regulate nerve blood flow within this period.