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

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.

The ultrastructure of the saccus vasculosus of teleost fishes I. The coronet cell

The ultrastucture of the coronet cell of a large number of teleosts belonging to different orders was investigated. Tubular and vesicular components of the smooth endoplasmic reticulum occur in coronet cells and in globules of all the species examined. Cell organelles such as lysosomes, Golgi systems, and mitochondria are predominantly located in the basal region of the cell. Modifications of the endoplasmic reticulum include whorls and vacuoles as well as honeycomb systems. In malacopterygian teleosts rootlets and filaments instead of microtubules occur frequently. The possibility of interconversion between these organelles is discussed. Acid phosphatase is found mainly in the lysosomes, but the granules contained in the stalked globules often contain acid mucopolysaccharide. It is suggested that new globules are formed by a process of pinching off of parts of the apical protrusion and the simultaneous growth of a modified cilium into it.

The Histochemistry of the Saccus Vasculosus of Notopterus Chitala (Teleostei)

The saccus vasculosus of Notopterus chitala is situated posteriorly to the pituitary gland. It consists of a number of loculi surrounded by blood sinusoids. The loculi open into a number of collecting channels which unite and ultimately drain into the third ventricle of the brain. The loculi are lined by a layer of pear-shaped ‘coronet cells’. The coronet cell has an apical protrusion provided with hairs, each ending in a globule. The coronet cells contain glycogen, especially in the apical protrusions and in the globules. Phospholipid, alkaline phosphatase, and mitochondria are concentrated in the apical protrusion and globules. There are also mitochondria round the nucleus. The Golgi element is not only present in the characteristic Golgi zone but occasionally round the nucleus as well. It has been stated by other authors that acid mucopolysaccharides are synthesized in the coronet cells of the rainbow trout and ‘secreted’ into the lumen of saccus vasculosus. However, acid mucopolysaccharides are not histochemically demonstrable in the coronet cells of Notopterus. The observations recorded in this paper indicate that the coronet cells in the saccus vasculosus of Notopterus are secretory and that glycogen is abundant in them.