LOCALIZATION OF ORNITHINE DECARBOXYLASE (ODC) IN THE COCHLEA OF THE IMMATURE RAT

Ornithine decarboxylase (ODC), the rate-limiting enzyme in polyamine s ynthesis, is important in cochlear development. Whereas tissue specifi c differences in cochlear ODC activity have been demonstrated, cellula r localization of ODC protein in the inner ear of the immature rat has not. ODC was localized in inner ear structures using an ODC polyclona l antibody and the effects of cycloheximide on ODC immunoreactivity an d enzymatic activity were determined. Tissues demonstrating elevated e nzymatic activity contained cells with the strong immunoreactivity. OD C activity was highest in the organ of Corti and lateral wall followed by the cochlear nerve. Immunoreactivity was demonstrated throughout t he cochlea with intense staining of the hair cells, pillar cells, Deit er's cells, inner sulcus cells, basilar membrane, stria vascularis, sp iral ganglion cell bodies and cochlear nerve fibers. Cycloheximide rap idly diminished cochlear ODC activity and expression of ODC protein. T he half-life of cochlear ODC was 30 min. Localization of cellular site s of ODC is important in understanding the role of the ODC-polyamine p athway in cochlear development and will be a valuable marker for tissu e damage from ototoxic agents.