Ultrastructure of the neural component of the regenerating spinal cord in the tails of three species of New Zealand lizards ( Leiolopisma nigriplantare maccanni , Lampropholis delicata , and Hoplodactylus maculatum )

The regenerated spinal cords of all three species examined ( Leiolopisma nigriplantare maccanni, Lampropholis delicata, Hoplodactylus maculatum ) consisted of a monolayer of ependymal cells with interspersed axons and cellular processes lining the liquor‐filled canalis centralis with its Reissner fibre in the centre. Cerebral spinal fluid contacting neurons (CSFCNs) were distinguishable from ependymal cells by their luminal projections, longer and thicker stereocilia (with well‐developed cytoskeletal elements), overall greater electron translucency, and specific organelles like silver methenamine‐positive dense granules. Silver methenamine‐positive material was present also in the lumen. Vesicles, apparently rupturing, were noticed on the luminal face of the CSFCN. A secretory activity of the CSFCN is one likely function of vesicles. The similarity between CSFCNs and inner ear hair cells (as well as lateral line receptor cells) suggested another possible function, namely that of monitoring cerebrospinal fluid flow. A third possibility is that the CSFCN is directly involved in creating movements in the cerebrospinal fluid. Whatever the precise function, synaptoid membrane specialisations in the CSFCN somata and axonal outgrowths into the ependymal interstices, establish beyond doubt that the CSFCN contributes to the neuropil in the regenerating spinal cord. Lipofuscine‐ like material was encountered exclusively in CSFCNs of older regenerates (1 year or more) suggesting that the organisation of the cells in the regenerating spinal cord varies with age.