MARGINAL CELLS IN THE SPINAL-CORD OF 4 ELASMOBRANCHS (TORPEDO-MARMORATA, T-TORPEDO, RAJA-UNDULATA AND SCYLIORHINUS-CANICULA) - EVIDENCE FORHOMOLOGY WITH LAMPREY INTRASPINAL STRETCH-RECEPTOR NEURONS

This study reports for the first time the presence of marginal cells, probably with stretch receptor function, in the spinal cord of four el asmobranch species, two electric rays, Torpedo marmorata and T: torped o, the skate Raja undulata and the dogfish Scyliorhinus canicula. In a ll four species, the marginal cells were located close to the laterove ntral surface of the cord and possessed thick dendrites which formed p art of characteristic glomerular structures. In vitro retrograde label ling of the spinal cord of the dogfish with horseradish peroxidase (HR P) showed that some of these cells have contralateral projections. Ult rastructural study of normal and retrograde HRP-labelled material show ed that the glomerular dendrites of marginal cells give rise to numero us fingerlike structures and are associated with a rich plexus of nerv e terminals, Characteristically, these dendrites contain numerous mito chondria. Immunocytochemical studies revealed a rich plexus of somatos tatin- and GABA-immunoreactive fibres in the glomeruli. These results strongly suggest that the marginal cells of the elasmobranch spinal co rd are stretch receptors homologous to lamprey edge cells and to the m arginal nucleus cells of the spinal cord of urodeles and snakes. We di scuss the possible role of these cells in the modulation of swimming m ovements.