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-target relation of sensory peptidergic nerve fibers in healthy and diseased osseous tissues, Bone tissue sections were immunoelectronmicroscopically investigated for calcitonin gene-related peptide (CGRP), a neuropeptide widely distributed in sensory peptidergic fibers, Ultramorphological relation of the osseous CGRP-immunoreactive (ir) nerve terminals and their target cells was comparatively analyzed using healthy, arthritic, and postarthritic bone specimens from control and adjuvant-induced arthritic rats, Terminal-like profiles of the osseous CGRP-ir axons were evidenced in direct contact with the metaphyseal osteoblasts and osteoclasts of the control animals, Terminal-like profiles were also noted in the vicinity of the periosteal lining cells, Nonterminal-like profiles did not make intimate spatial relation to the cells/structures surrounding the nerve, Osseous CGRP-ir terminals and axons, which are either uncovered or thinly ensheathed by the supportive tissues? were extensively degenerated in adjuvant-induced infiltration, whereas larger fibers were relatively resistant, Numerous CGRP-ir axons with distinctive features reinnervated the postarthritic, ossifying periosteum, CGRP-ir axons appeared to reinnervate the eroded surface of metaphyseal bone and cartilage as early as the recruited osteoblasts resume osteogenesis in the postarthritic metaphysis. The observed terminal-target relations in the healthy and diseased bone tissues give an ultramorphological basis for the putative trophic, modulatory actions of CGRP innervation of the bone cells.