Morphological and physiological findings on hair cells with impaired metabolism (nitrogen, monoiodoacetate) in Caiman crocodilus with reference to sudden deafness.

Morphological and physiological studies were carried out on Caiman crocodilus under experimentally produced metabolic changes. During N2-respiration the cochlear potentials responded differently. The negative component (CM-) of the cochlear microphonics decreased continuously, whereas the CM+ component showed only a little change. The summation action potential (AP) exhibited a similar behaviour to that of CM-. These alterations were reversible up to periods of 30 min N2-respiration. The morphological findings, after N2-respiration, showed an intracellular oedema of the hair cells. The afferent synaptic contacts are always recognizable. Different degrees of disintegration within the presynaptic structures were seen. Efferent axosomal and axodendritic synapses were unchanged. MIA-perfusion led to an irreversible decrease of the cochlear potentials (CM+; CM-; AP) and morphologically to a total destruction of the papilla basilaris. The changes in the presynaptic structures during anaerobic metabolism offer the possibility of a new explanation for the reversibility of sudden deafness.