Adrenergic innervation of the tibial and vagus nerves in rats of different ages.

Adrenergic nerve fibers innervating blood vessels in the epi-perineurium and endoneurium of the tibial and vagus nerves of male Fischer-344 rats of different ages were examined using formaldehyde-induced fluorescence technique and fluorescence microscopy. Between 6 and 24 months of age, no significant difference in the mean density of perivascular innervation in the epi-perineurium of the nerves was found, whereas between 24 months and 30 months the density decreased in both nerve types. The intensity of noradrenaline fluorescence of nerve fibers also was decreased in the oldest age group. In the endoneurium, the density of adrenergic nerve fibers was reduced by 57% at 24 months, and by more than 98% at 30 months as compared with 18 months. Age-related differences were similar in the tibial and vagus nerves. The results suggest that adrenergic neuronal control of the microcirculation in the rat tibial and vagus nerves is lost during aging as it is in other organs of the cardiovascular system.