INNERVATION OF THE EQUINE MATURE AND IMMATURE PROXIMAL SESAMOID BONE BY CALCITONIN-GENE-RELATED PEPTIDE AND SUBSTANCE P-CONTAINING NERVES

Objective-To localize and determine relative frequency of occurrence o f calcitonin gene-related peptide (CGRP) and substance P (SP) fibers i n the proximal sesamoid bones (PSB) and adjacent structures in sound h orses. Sample Population-4 foals and 3 adult horses. Procedure-Medial PSB and adjacent ligaments of both forelimbs were collected, flushed, and fixed in buffered 4% formalin. The left PSB were cut into 5 longit udinal, sagittally oriented slabs, and the right PSB were cut into 5 t ransverse slabs. After decalcification in EDTA, slices were transferre d to a 30% sucrose solution, deep frozen, sectioned (80 mu m), and sto red in Tris-buffered saline solution for free-floating immunocytochemi cal processing, staining of which was performed by use of the peroxida se-antiperoxidase method with polyclonal rabbit antibodies against CGR P and SP Sections were examined by light microscopy. Results-Calcitoni n gene-related peptide and SP fibers were present throughout the PSB; in ligaments, they were concentrated at the attachment sites. Presenta tion of the fibers, the innervation pattern, and intensity in the bone s of horses differed from that in foals, in which the fibers were more delicate and frequency of occurrence was lower. in horses, innervatio n with CGRP and SP fibers was more dense in the periphery of the bone, whereas in foals, local difference in innervation of the bone was not evident. With the exception of the intersesamoidean ligament, ligamen ts were more richly innervated than was bone. Conclusion-Presence of t he nociceptive peptides CGRP and SP indicated that the PSB and, more p ractically, the adjacent ligaments are sensitive structures.