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.
Imai
S
S
Department of Bioscience, Helsinki University, Finland.
Rauvala
H
H
Konttinen
Y T
YT
Tokunaga
T
T
Maeda
T
T
Hukuda
S
S
Santavirta
S
S
D000818:Animals; D001169:Arthritis, Experimental / Q000378:metabolism* / Q000473:pathology; D001842:Bone and Bones / Q000294:innervation* / Q000378:metabolism / Q000473:pathology; D015740:Calcitonin Gene-Related Peptide / Q000378:metabolism*; D004525:Efferent Pathways / Q000378:metabolism / Q000473:pathology; D007150:Immunohistochemistry; D008297:Male; D016253:Microscopy, Immunoelectron; D009411:Nerve Endings / Q000378:metabolism / Q000473:pathology; D009412:Nerve Fibers / Q000378:metabolism* / Q000473:pathology; D051381:Rats; D011917:Rats, Inbred Lew; D017208:Rats, Wistar
D015740:Calcitonin Gene-Related Peptide