H3-THYMIDINE LABELED CEREBROSPINAL-FLUID CONTACTING CELLS IN THE REGENERATING CAUDAL SPINAL-CORD OF THE LIZARD LAMPROPHOLIS

Australian scincid lizards (Lampropholis) were injected with a single dose of H3-thymidine during the early stages of tail regeneration in order to study later a possible differentiation of neurons and glial cells within the regenerating spinal cord. After 5 hours post-injection only electrondense or pale ependymal cells took up H3-thymidine. Light and electron microscopic analysis of later stages, 6, 12 and 20 days post-injection, revealed that labeled pale cells were occasionally recognizable 12-20 days post-injection. Many pale unlabeled and a few labeled cells contacted the central canal of the spinal cord and appeared as cerebrospinal fluid contacting cells. The electron microscope showed the presence of stereocilia in the apical cytoplasm of these pale cells, a typical characteristic of cerebrospinal fluid contacting neurons. After 12-20 days post-injection, among ependymal cells rare pale cells containing intermediate filaments were labeled. Other pale cells represented intermediate stages of differentiation between ependymal and neural or glial cells. Differentiated medium-high electrondense ependymal tanicytes were also labeled 6, 12 and 20 days post-injection. This analysis showed that a limited regeneration of cerebrospinal fluid contacting neurons occurs locally in the caudal spinal cord of the scincid lizard Lampropholis.