Recent studies have demonstrated that bone is highly innervated and contains neuromediators that have functional receptors on bone cells. However, no data exist concerning the quantitative changes of innervation during bone loss associated with
estrogen withdrawal. To study the involvement of nerve fibers in the regulation of bone remodeling, we have evaluated the modifications of innervation in a classical in vivo model of
osteopenia in rats,
ovariectomy (OVX). Skeletal innervation was studied by immunocytochemistry using
antibodies directed against specific neuronal markers,
neurofilament 200 and
synaptophysin, and the neuromediator
glutamate. Sciatic
neurectomy, another model of bone loss due to limb
denervation and
paralysis, was used to validate our quantitative image analysis technique of immunostaining for nerve markers. Female Wistar rats at 12 wk of age were
sham-operated (
SHAM) or ovariectomized (OVX). Bone mineral density measurement and bone histomorphometry analysis of tibiae 14 d after surgery demonstrated a significant bone loss in OVX compared with
SHAM. We observed an important reduction of nerve profile density in tibiae of OVX animals compared with
SHAM animals, whereas innervation density in skin and muscles was similar for OVX and control rats. Quantitative image analysis of immunostainings demonstrated a significant decrease of the percentage of immunolabeling per total bone volume of
neurofilament 200,
synaptophysin, and
glutamate in both the primary and secondary spongiosa of OVX rats compared with
SHAM. These data indicate for the first time that OVX-induced bone loss in rat tibiae is associated with a reduction in nerve profile density, suggesting a functional link between the nervous system and the bone loss after
ovariectomy.