S-100 protein-immunoreactive structures in the brains of the elasmobranchs Scyliorhinus torazame and Mustelus manazo.

S-100 protein-immunoreactive structures were investigated in the brains of two species of elasmobranchs, Scyliorhinus torazame and Mustelus manazo. In both species, immunoreactivity for S-100 protein was seen widely in the brain. It was localized in astrocytes and tanycytes; superficial glial membrane, vascular endfeet, and radial fibers were recognized clearly. However, no immunoreactivity was found in the ependymal cells of non-tanycyte type, which were located in the choroidal plexus, subcommissural organ, and saccus vasculosus. No neuronal cells showed S-100 protein immunoreactivity. Immunoelectron microscopy revealed that the antigen was present diffusely in the cytoplasmic matrix of the cells and also associated with the plasma membrane, outer membrane of mitochondria, and microtubule-like components.