Fine structure of regenerated ependyma and spinal cord in Sternarchus albifrons

Abstract

The caudal-most regenerated spinal cord in Sternarchus albifrons consists solely of an ependymal tube. Ependymal cells are enlarged radially and are more numerous than in unregenerated cord. Projections of ependymal cell cytoplasm and Reissner's fiber fill most of the central canal. Small groups of neurites and cell processes filled with dense-cored vesicles lie between abluminal processes of ependymal cells. Rostral to this, additional cells appear dorsal and lateral to the inner ependymal layer. Some cell bodies contain numerous dense-cored vesicles. Larger bundles of neurites, some with synapses, are present. Invaginations of the peripheral edge of the cord create enclosed spaces lined with basal lamina. In the peripheral region, longitudinally oriented neurites extend through extracellular spaces or channels. The ventral portion at some levels of regenerated cord is completely filled with neurites, processes containing dense-cord vesicles, and capillaries. Similar masses of neurites and processes containing dense-cored vesicles lie outside the cord proper, in or near the meningeal layer. In rostral-most sections, the organization of regenerated spinal cord approaches that of normal cord, with the regenerated cord exhibiting groups of myelinated axons, differentiated fibrous astrocytes and oligodendroglia, cell bodies containing dense-cored vesicles, and differentiated electromotor neurons. These observations indicate a degree of pluripotency in some of the ependymal cells in adult Sternarchus. Moreover, they are consistent with a role of ependymal cells in the guidance of regenerating neurites.

Adult Neurogenesis and Neuronal Regeneration in the Central Nervous System of Teleost Fish

“…More rostrally, additional layers of cells surround the central canal. In this region, the cells differentiate into neurons and glia, as suggested by both ultrastructural [Anderson et al, 1983] and immunohistochemical [Anderson et al, 1987[Anderson et al, , 1994 studies. The regenerated electromotor neurons exhibit a morphology resembling that of electromotor neurons in non-regenerated parts of the spinal cord [Anderson and Waxman, 1981].…”

“…New cells are produced at the caudal end of the regenerating cord, whereas rostrally to this region where the older cells are located differentiation takes place. Based on ultrastructural observations Anderson et al [1983] proposed the source of new cells to be ependymal cells. Caudalmost, the regenerated cord consists of an ependymal tube composed of a single layer of cells.…”

Ependyma of the Rat Fourth Ventricle and Central Canal: Response to Injury

“…32. 33], although neuritic regeneration has also been observed in their absence [4,26]. Although described primarily in connection with ependyma of amphibians and reptiles, this phenomenon has also been noted in mammals.…”

Reaction of spinal cord central canal cells to cord transection and their contribution to cord regeneration

“…In contrast, the ventricular cells of adult anamniotes retain considerable proliferative ability (Simpson, 1964;Egar and Singer, 1972;Nordlander and Singer, 1978;Singer et al, 1979;Anderson et al, 1983) and appear to contribute to the neural regeneration seen in these animals. Simpson (1964), for example, found that, if this region has been destroyed, the tail of the lizard Lygosoma does not regrow after amputation.…”

“…Spinal cord regeneration following tail amputation has been well studied in anamniotes (see, e.g., Nordlander and Singer, 1978;Anderson and Waxman, 1983a;Anderson et al, 1983;Benraiss et al, 1997). The spinal cord regrows within a blastema that is dominated by an ependymal outgrowth (Simpson, 1983), thought to create a cellular scaffold that guides and supports the growing axons (the "blueprint" hypothesis; Singer et al, 1979).…”