LONG-TERM AGE-RELATED CONSEQUENCES OF FORELIMB DAMAGE UPON EXPRESSIONOF PRIMARY AFFERENT PHENOTYPES IN THE CERVICAL DORSAL HORN

Rats that sustained forelimb removal on either embryonic day 16 (E-16) or the day of birth (P-0), or transection of the brachial plexus in a dulthood, had sections through the cervical dorsal horn stained for ga lanin, calcitonin gene-related peptide (CGRP), or the plant lectin Ban dieria simplicifolia-I (BS-I) 35-50 days after these lesions. The resu lts of these experiments demonstrated age-related differences in the e ffects of peripheral nerve damage upon the distributions of each of th ese three primary afferent markers in the dorsal horn. Damage to the b rachial plexus in adulthood caused a significant increase in the densi ty of galanin immunoreactivity in the medial portion of layers I and I I and the appearance of galanin immunoreactivity in layers III and IV of the cervical dorsal hem. Such lesions resulted in significant reduc tions in the density of CGRP immunoreactivity in layers I and II and o f BS-I binding in lamina II. Forelimb removal on the day of birth resu lted in no significant change in the density of galanin immunoreactivi ty in layers I and Il, but in the appearance of galanin-immunoreactive fibers in layers III-V. Neonatal forelimb removal resulted in no sign ificant change in the density of CGRP immunoreactivity in layers I and II, but in a significant reduction in the density of BS-I binding in the medial portion of lamina II. Removal of the forelimb on E-16 cause d a significant increase in the density of galanin immunoreactivity in layers m-V, but had no significant effect on the density or distribut iuon of either CGRP immunoreactivity or BS-I binding in the cervical d orsal horn. These results suggest that peripheral nerve damage at all ages may cause an up-regulation of galanin in a wider distribution of ganglion cell types than was previously thought to be the case, and th at there are different sensitive periods for lesion-induced, long-term changes in the innervation of the dorsal horn by CGRP- and BS-I-posit ive primary afferent axons.