Fine structure of regenerating caudal spinal cord in adult tuatara (Sphenodon punctatus).

A report on the presence of cerebrospinal fluid contacting neurons (CSFCN) inside the regenerating caudal spinal cord of adult specimens of the tuatara Sphenodon punctatus is given. The cells in question are easily distinguished from amongst ependymal tanicytes of the regenerating cord. Large granules of high electron density are particularly common in these neural cells which generally show clear cytoplasm of low electron density. The ultrastructural findings strongly support the idea of a secretory activity of these neurons directed toward the central canal.