Spontaneous mineralization of the sciatic nerve of senescent rats.

A spontaneous mineralization of the sciatic nerve of senescent specific pathogen-free-bred rats (aged 42 months) is reported. Deposits were found in the endoneurium of different branches of the nerve at mid-thigh level. They appeared as small discrete deposits or as large tubular-shaped concretions, probably formed by the growth and merger of the smaller deposits. Some of the concretions were found in close proximity to blood vessels. Deposits consisted of dense aggregations of randomly entangled spicules spreading within bundles of collagen fibrils. Calcium was detected by histochemistry and X-ray dispersion microanalysis. Phosphorus was also found, possibly associated with calcium to form hydroxyapatite.