Protein kinase C beta-subtype-immunoreactive motor and sensory nerves in rat muscle spindle.

The localization of protein kinase C beta-subtype-like immunoreactivity (PKC-beta-LI) was studied in the muscle spindles of rat neck muscles. In the equatorial regions of muscle spindles PKC-beta-LI was detected in spiral sensory nerve endings surrounding intrafusal muscle fibers. In polar regions single PKC-beta-immunoreactive (IR) nerve fibers were found between intrafusal muscle fibers and some PKC-beta-IR motor nerve endings were seen on the surface of intrafusal fibers. These results suggest that PKC-beta may be involved in regulation of muscle contraction and tonus by modulating the sensitivity of afferent and efferent innervation of muscle spindles.