Reinnervation of denervated Pacinian corpuscles: ultrastructural observations in rats following free nerve grafts.

Abstract

Nerve transection and immediate free nerve grafts using rat sciatic nerves were employed to observe the morphologic changes in periodical denervation and reinnervation of Pacinian corpuscles located on the interosseous membrane between the fibula and tibia. During periods of from 2 weeks to 20 months after the surgery, a total of 28 corpuscles were obtained under an operating microscope and processed for morphologic analysis using light and electron microscopes. Based on our morphologic findings, normal corpuscles were composed of an axon terminal and inner and outer cores. The axon terminal disappeared within 2 weeks after the nerve grafts, but the original inner and outer core cells remained for up to 20 months. In addition, a small number of collagen fibrils was observed between the inner and outer core cells. After 4 months, multiple axon terminals began to regenerate in the inner core. From 7 to 20 months, these axon terminals in some corpuscles developed a structure resembling that of normal terminals. Some of these terminals were located in the center of the inner core, but a few were in contact with the outside of the inner core. The production of collagen fibrils in denervated corpuscles was periodically activated in the intercellular spaces. These findings suggest that the morphologic changes in denervated corpuscles correspond to those in denervated nerves. Inner core cells, which are continuous with Schwann cells, remain in their original condition in denervated corpuscles until regenerating nerves enter the inner core and are essential for corpuscle regeneration, because they may produce some trophic substances that induce the regeneration of multiple axon terminals.(ABSTRACT TRUNCATED AT 250 WORDS)