Localization of neurocalcin-like immunoreactivity in rat cranial motoneurons and spinal cord interneurons.

Neurocalcin (NC) is a calcium-binding protein with at least three putative calcium-binding domains called EF-hands. In this study, the distribution of neurocalcin-like immunoreactivity (LI) was examined in the rat motor system. Motoneurons in the III, IV and VI cranial nerve nuclei were NC-immunoreactive (IR) and strong labelling was seen in the nerve bundles and in the myoneural junctions in all extraocular muscles. In the ventral horn of the spinal cord, interneurons were NC-IR, whereas motoneurons, identified by Fluorogold tracing, were unlabelled. A large number of NC-IR neurons was present in the dorsal horn. NC-IR nerve fibers were seen in the ventral roots and, more abundantly, in the dorsal roots. The present results demonstrate NC-LI in the supraspinal motoneurons and spinal cord interneurons, both of which are fast-firing neurons. Provided neurocalcin regulates the concentration of free intracellular Ca2+, it may participate in several cellular functions in the fast-firing neurons.