Morphological study of blood-labyrinth barrier in the vestibular organs under normal and experimental acute hypertensive and acute hypotensive conditions.

In order to examine a blood-labyrinth barrier in the vestibular region, capillary permeability of the vestibular organs, i.e. the sacculus, the utriculus and the ampullae of semicircular canals, were studied light and electron microscopically by the horseradish peroxidase (HRP) tracer method. Intravenously infused HRP was not observed outside capillaries because of the tightness of endothelial tight junctions and the paucity of pinocytotic vesicles. Furthermore, the effect of drug-induced acute hypertension and acute hypotension on the capillaries of the vestibular organs was studied morphologically using the tracer technique. In each experiment, there was no extravasation of HRP from capillaries, thus agreeing with the results of the experiment made under normal conditions. These findings mean that capillaries of the vestibular region are of ordinary brain capillary type and contribute to the blood-labyrinth barrier to macromolecules such as HRP both under normal conditions and following abrupt changes in blood pressure.