Barrier systems in the inner ear.

Because of the highly complicated function of the central nervous system and sensory organs, barrier systems have necessarily developed to ensure stability of the extracellular fluids bathing these organs. Several barrier systems which can influence the composition of the inner ear fluids are discussed. They are the 1) blood-labyrinth barrier, 2) cerebrospinal fluid-labyrinth barrier, and 3) middle ear-labyrinth barrier. The experimental data are shown to indicate that these barriers serve to protect the inner ear through selective permeability. Arachidonic acid metabolites, particularly compounds of the prostaglandin series, were identified in perilymph, and were increased by the administration of stress-related hormones, and decreased after aspirin injection. The inner ear fluid composition responds to the changes of the surrounding fluid containing compartments. However, the degree of response appears to depend on the level of changes induced in the surrounding compartments. The concept of a threshold concentration of toxic substances in middle ear effusion to induce inner ear damage is also proposed.