EFFERENT TARGETS OF OSSEOUS CGRP-IMMUNOREACTIVE NERVE-FIBER BEFORE AND AFTER BONE DESTRUCTION IN ADJUVANT ARTHRITIC RAT - AN ULTRAMORPHOLOGICAL STUDY ON THEIR TERMINAL-TARGET RELATIONS

We report the ultramorphological characterization of the terminal-targ et relation of sensory peptidergic nerve fibers in healthy and disease d osseous tissues, Bone tissue sections were immunoelectronmicroscopic ally investigated for calcitonin gene-related peptide (CGRP), a neurop eptide widely distributed in sensory peptidergic fibers, Ultramorpholo gical relation of the osseous CGRP-immunoreactive (ir) nerve terminals and their target cells was comparatively analyzed using healthy, arth ritic, and postarthritic bone specimens from control and adjuvant-indu ced arthritic rats, Terminal-like profiles of the osseous CGRP-ir axon s were evidenced in direct contact with the metaphyseal osteoblasts an d osteoclasts of the control animals, Terminal-like profiles were also noted in the vicinity of the periosteal lining cells, Nonterminal-lik e profiles did not make intimate spatial relation to the cells/structu res surrounding the nerve, Osseous CGRP-ir terminals and axons, which are either uncovered or thinly ensheathed by the supportive tissues? w ere extensively degenerated in adjuvant-induced infiltration, whereas larger fibers were relatively resistant, Numerous CGRP-ir axons with d istinctive features reinnervated the postarthritic, ossifying perioste um, CGRP-ir axons appeared to reinnervate the eroded surface of metaph yseal bone and cartilage as early as the recruited osteoblasts resume osteogenesis in the postarthritic metaphysis. The observed terminal-ta rget relations in the healthy and diseased bone tissues give an ultram orphological basis for the putative trophic, modulatory actions of CGR P innervation of the bone cells.