Ontogeny of sensory and autonomic nerves in the developing mouse skeleton

Bone innervation is implicated in bone modeling and remodeling. This study investigates skeletal nerve development in embryonic and newborn mice, focusing on sensory and autonomic nerves and their temporal occurrence.

The ontogeny of innervation and angiogenesis in the hindlimb skeleton of mice was studied from embryonic day (E) 15 to postnatal day (P) 20. Neuronal tissue was immunohistochemically labeled for detection of growth associated protein 43 (GAP-43), protein gene product 9.5 (PGP 9.5), calcitonin gene-related peptide (CGRP), tyrosine hydroxylase (TH), and neuropeptide Y (NPY). Vascular endothelium was labeled for platelet endothelium cell adhesion molecule-1 (PECAM-1). Morphology was evaluated with hematoxylin and eosin staining.

GAP-43, PGP 9.5, CGRP, and PECAM-1 were all present at E 15, adjacent to areas with high osteogenic and chondrogenic activity. In the primary ossification centers, GAP-43 was found at E 15, PGP 9.5 at E 17, CGRP at E 19, and NPY at P 4. The same time lag in appearance was observed in the secondary ossification centers. The covering capillary network was initially dense, but became mature and sparse from P 12 onwards.

A functional nerve supply co-localized with a rich capillary network is seen early in the developing mouse skeleton, especially in areas with high osteogenic activity. Sensory innervation occurs prior to partus, while autonomic innervation (revealed by the presence of NPY and TH) is established post partum. The findings indicate a time-related development of nerves with different qualities, according to skeletal development.