Intraventricular blood vessels of the hypothalamus of Salmo gairdneri and Gambusia affinis.

The ultrastructure of the hypothalamic intraventricular blood vessels is studied in two fish: Salmo gairdneri, a primitive teleost and Gambusia affinis, a modern teleost. Morphological differences found between vessels belonging to the lateral and medial recesses in Salmo are described as well as contrasted with those of Gambusia. The endothelial cells are joined by elaborate tight junctions in both teleosts and also by desmosomes in Gambusia. These vessels are continuous capillaries with pericytes which lack junctional complexes. The perivascular cells of the larger vessels display morphological characteristics of myoid cells.