Effects of chronic XXXX treatment and age on cell division in the adult gerbil inner ear.

@entity1603 @entity16811 @entity274 @entity1483 @entity393
Atrophy of the stria vascularis and spiral ligament and an associated decrease in the endocochlear potential (EP) are significant factors in age-related @entity393 (presbyacusis). To model this EP decrease, @entity1483 was delivered into the round-window niche of young adult gerbils by osmotic pump for seven days, chronically reducing the EP by 30-40 mV. Compound action potential (CAP) thresholds were correspondingly reduced by 30-40 dB @entity16811 at high frequencies. Two weeks after withdrawal of @entity1483 , the treated ears showed an EP recovery of up to 20-30 mV along with a similar recovery of CAP thresholds. The influence of cell division on @entity1483 -induced and age-related decline of the EP was examined using a mitotic tracer, @entity1603 ( @entity1603 ). Cell proliferation was examined in three groups: young control, @entity1483 -treated, and aged cochleas. Sections immunostained for @entity1603 were bleached with @entity274 to eliminate ambiguities with melanin pigment in the inner ear. Cell types positively labeled for @entity1603 in all three groups included Schwann cells in Rosenthal's canal; glial cells in the osseous spiral lamina; fibrocytes in the limbus, sacculus, and spiral ligament (SL); epithelial cells in Reissner's and round-window membranes; intermediate cells in the stria vascularis; and vascular endothelial cells. Quantitative analysis showed that the mean number of @entity1603 -positive ( @entity1603 +) intermediate cells in the stria did not differ significantly among the three groups. In contrast, there was a significant increase of @entity1603 + fibrocytes in the SL of @entity1483 -treated animals as compared to the young control group. Moreover, there was a significant decrease in labeled fibrocytes in the aged versus the young ears, particularly among the type II and type IV subtypes. The results suggest that the increased fibrocyte turnover in the SL after @entity1483 treatment may be related to the recovery of EP and CAP thresholds, supporting the hypothesis that fibrocyte proliferation may be essential for maintaining the EP and cochlear function in normal and damaged cochleas. Moreover, the decreased turnover of SL fibrocytes with age may be a contributing factor underlying the lateral wall pathology and consequent EP loss that often accompanies presbyacusis.
