The permeability of blood vessels of the modiolus, especially cochlear plexus, in rats and guinea pigs has been studied ultrastructually by tracer experiments with horseradish peroxidase (HRP). Extravasation of intravenously injected HRP spread into intercellular spaces, but not outside the cochlear plexus. The capillary endothelium showed fenestrae with single-layered diaphragm, high distribution of labelled pinocytotic vesicles and penetration of HRP through endothelial tight junctions. On the other hand, blood vessels within the modiolus except for the cochlear plexus did not allow to leak HRP.
These findings suggest that tight junctions bordering the cochlear plexus play a role in a part of the blood-perilymph barrier, whereas other blood vessels within the modiolus themselves act as the barrier.
