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Abstract
Changes in the integrity of cochlear ion transport systems with age were examined
in gerbils raised for 5-38 months in a quiet environment. Ion transport function was
assessed by light microscopic immunohistochemical staining for the enzyme, Na,K-ATPase
and by measurement of the endocochlear potential (EP). Small foci of strial atrophy
accompanied by loss of immunostaining for Na,K-ATPase were observed in the stria vascularis
of the apical and basal turns as early as 5 months of age. Cochleas from 29-38 month-old
gerbils showed a loss of immunostaining for Na,K-ATPase in the stria in most of the
apical turn with the degeneration extending well into the middle turn in many of the
oldest ears. The extent of strial atrophy and loss of immunoreactive Na,K-ATPase in
the basal turn varied considerably among the oldest cochleas. Populations of lateral
wall fibrocytes (type II fibrocytes) normally rich in Na,K-ATPase exhibited a corresponding
decrease in enzyme content in regions of advanced strial atrophy. The volume of immunostained
stria vascularis correlated well with the magnitude of the resting EP. The results
demonstrate that lateral wall ion transport systems in the gerbil cochlea degenerate
as a function of age. The findings also provide good evidence for a functional relationship
between the stria vascularis and the Na,K-ATPase-rich type II fibrocytes in generating
and maintaining the EP.