Regeneration of supraependymal nerve fibers in rat.

Factors intrinsic and extrinsic to the neurons regulate the regeneration of axons following axotomy. Elucidation of these mechanisms will provide fundamental information on the regulation of growth in mammalian neurons. To understand the role of environmental factors in nerve regeneration, this study focuses on the axotomy-induced regeneration of supraependymal nerve fibers that inhabit an environment different from other central nervous system neurons and the neurons of the peripheral nervous system. These fibers are ideally located to receive various neuroactive substances that are streaming in the cerebrospinal fluid. Transmission electron microscopic studies reveal the presence of three types of fibers on the ventricular surface. They are fibers with clear synaptic vesicles, those containing small dense core vesicles together with clear synaptic vesicles and fibers containing large dense core granules. To study the regenerative potential of supraependymal nerve fibers, they were axotomized by inflicting mechanical injury to the floor of the third ventricle. Following axotomy, the regenerative ability of the supraependymal nerve fibers was monitored between five and thirty days, by scanning electron microscopy. By the fifth day, there was a noticeable increase in the neuronal network that gradually increased throughout the experimental period. The regenerative ability of supraependymal neurons, as compared with other neurons in the central nervous system, could be due to the differences in their environment. These studies suggest that mammalian cerebral ventricles may be an adequate site for neural transplantation.