AUTONOMIC AND SENSORY REINNERVATION OF SMOOTH-MUSCLE TRANSPLANTED TO THE ANTERIOR-CHAMBER OF THE EYE - EFFECT OF TARGET POSTNATAL AGE

The ability of the nervous system to provide target innervation is gre atest in early development, but decreases as a function of age, The ob jective of the present study was to determine if age-related changes o ccurring within the target tissue contribute to this decline. Periorbi tal tarsal smooth muscle from donor rats 6, 14, 30, and 48 days postna tal were transplanted to the anterior chamber of the eye of 84- to 90- day-old host rats. The tissue was removed at 3, 6, or 10 days post-tra nsplant and immunostained for presumptive sympathetic nerves (dopamine beta-hydroxylase-immunoreactive, DBH-ir), sensory (calcitonin gene-re lated peptide-immunoreactive, CGRP-ir) or parasympathetic (vasoactive intestinal polypeptide-immunoreactive, VIP-ir). DBH-ir sympathetic fib ers sprouted into target from donors of all ages. However, the rate of ingrowth was most rapid in tissue from g-day-old donors. In contrast, CGRP-ir sensory fibers showed no age-related differences, but grew mo re rapidly than sympathetic fibers. However, the innervation density a t 10 days was comparable for both types of nerves. No significant VIP ir parasympathetic ingrowth could be demonstrated at any age. We concl ude that smooth muscle target in developing animals can have selective effects on different populations of ingrowing fibers; the rate of sym pathetic ingrowth declines with maturity, whereas ingrowth of sensory fibers is not altered. (C) 1994 Academic Press, Inc.