Morphological Aspects of the Subcommissural Organ of Reptiles

Abstract

Our histochemical and ultrastructural studies on the subcommissural organ (SCO) of reptiles have revealed the following results:

• 1. At least in the snake Natrix maura, two clearly different ependymal cell populations coexist in the SCO. Hypendymal cells were virtually absent. Most cells of the organ display secretory features and are in contact with the cerebrospinal fluid, blood vessels, and the leptomeninges; they release a flocculent material into the ventricle. Some cells of the dorsal groove in the caudal third of the organ are not stained with aldehyde fuchsin. However, they contain electron-dense granules originating from the Golgi apparatus. These granules are released into the ventricle. This type of cell is under investigation in our laboratory in other reptilian species.

• 2. The blood vessels encompassed by the endfeet of the SCO cells display some peculiarities in turtles and in Natrix maura. The wide perivascular spaces are arranged in a labyrinthine pattern. In these labyrinths scattered collagenous fibrils and nerve endings have been observed.

• 3. In both species the SCO probably exhibits monoamine-containing fibers. However, axonal endings located between the apical portions of SCO cells have been observed exclusively in turtles. In addition, peptidergic nerve fibers may be present in the SCO of the snake.

• 4. Preliminary data indicate seasonal differences in the secretory activity of the SCO of snakes and turtles. In winter the secretory products are apparently accumulated in the cells of the SCO. This may be due to a decreasing release of secretory material.