Neurocalcin-immunopositive nerve terminals in the muscle spindle, Golgi tendon organ and motor endplate.

The present study revealed the immunohistochemical distribution of neurocalcin, a three EF-hand calcium-binding protein, in the rat muscles and tendons. In the muscle spindles, annulospiral endings, which made spirals around the intrafusal muscles, showed intense neurocalcin-immunoreactivity. In the Golgi tendon organs, immunopositive thick nerve fibers entered the collagenous fibers resulting in the projection of many swelling terminals. In all examined muscles, nerve terminals in the motor endplates showed neurocalcin-immunoreactivity associated with the membranes of synaptic vesicles and mitochondria. These findings suggest that neurocalcin is distributed and regulates calcium signaling in both afferent and efferent nerve terminals in the muscles and tendons.