Effects of capsaicin-induced sensory denervation on osteoclastic resorption in adult rats.
Many recent findings suggest that the nervous system has efferent effects on bone. A putative role of the sensory innervation has been assessed by using a synchronised rat model of bone resorption after treating adult animals with the neurotoxin capsaicin. Fourteen days after capsaicin treatment (50 mg kg-1) the right maxillary molars were extracted to activate a wave of resorption along the mandibular cortex. The rats were killed 4 days later (i.e. at the peak of resorption in this model), and their right mandibles were processed for histometric evaluation of resorption along the cortex and of calcitonin gene-related peptide (CGRP)- and substance P (SP)-immunoreactive (IR) fibres in the dental pulp. CGRP-IR and SP-IR fibres were significantly reduced in numbers by the capsaicin treatment (by 58 and 49%, respectively), confirming the success of sensory denervation. The resorption surface was significantly reduced (P < 0.005) versus the sham-treated animals. Although the size of the osteoclast population recruited in the site was not modified, the number of actively resorbing osteoclasts was significantly reduced (P < 0.03). However, the activity of the resorbing cells was not modified. Non-specific esterase-positive osteoclast precursors were also significantly few after capsaicin treatment. These data show that the sensory nervous system is involved in the control of bone resorption at two different levels: (1) in the recruitment of osteoclast precursors, and (2) in regulating the access of recruited cells to the bone surface.
Adam
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C
Laboratoire de Biologie et Physiopathologie Crânio-Faciales, Groupe Physiopathologie Osseuse, Faculte de Chirurgie-Dentaire, Universite Rene Descartes (Paris V), 1 rue Maurice Arnoux, 92120 Montrouge, France.
Llorens
A
A
Baroukh
B
B
Cherruau
M
M
Saffar
J L
JL
D000818:Animals; D001862:Bone Resorption / Q000473:pathology / Q000517:prevention & control*; D015740:Calcitonin Gene-Related Peptide / Q000502:physiology; D002211:Capsaicin / Q000494:pharmacology*; D003714:Denervation; D003782:Dental Pulp / Q000187:drug effects / Q000502:physiology; D007150:Immunohistochemistry; D008297:Male; D008437:Maxilla / Q000473:pathology; D009412:Nerve Fibers / Q000187:drug effects / Q000502:physiology; D009475:Neurons, Afferent / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar; D013373:Substance P / Q000502:physiology
D013373:Substance P; D015740:Calcitonin Gene-Related Peptide; D002211:Capsaicin