The distribution pattern of horseradish peroxidase (HRP) in the inner ear after injection into the middle ear cavity was studied using albino guinea pigs.
1) HRP is found in the round window membrane, organ of corti, spiral ligament, vestibular sense organs, dark cell area and endolymphatic sac.
2) No HRP is found in the stria vascularis.
3) The distribution pattern of HRP in the labyrinth is similar for both injection routes, that is the middle ear cavity and scala tympani.
4) The main route of HRP passage into the perilymphatic space from the middle ear cavity is through the round window membrane.
Another possible route is the oval window.