The ultrastructure of the saccus vasculosus of teleost fishes III supporting tissue, innervation, vascularization

Abstract

The ultrastructure of the supporting cells, the nerve fibres, and the blood vessels of the saccus vasculosus was investigated. Apart from the apical protuberance, the coronet cells are usually enveloped by thin sheets of supporting-cell cytoplasm. Although pinocytotic vesicles were not evident, the distal region of the supporting cells often contains cytoplasmic vesicles. The possibility of transfer of fluid by these cells is discussed. The network of nerve fibres contains both vesiculated and non-vesiculated nerve endings. Some of these endings lie adjacent to coronet cells and, occasionally, to supporting cells. In considering the function of the coronet cell undue emphasis was probably placed in the past on the possible possession of an axon and, also, on the vicarious presence of a secretory product in the lumen of the saccus vasculosus. It is suggested that the coronet cell could function as a chemoreceptor monitoring the composition of the cerebrospinal fluid.