Effects of Chronic Furosemide Treatment and Age on Cell Division in the Adult Gerbil Inner Ear

Abstract

Atrophy of the stria vascularis and spiral ligament and an associated decrease in the endocochlear potential (EP) are significant factors in age-related hearing loss (presbyacusis). To model this EP decrease, furosemide 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 SPL at high frequencies. Two weeks after withdrawal of furosemide, 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 furosemide-induced and age-related decline of the EP was examined using a mitotic tracer, bromodeoxyuridine (BrdU). Cell proliferation was examined in three groups: young control, furosemide-treated, and aged cochleas. Sections immunostained for BrdU were bleached with H 2 O 2 to eliminate ambiguities with melanin pigment in the inner ear. Cell types positively labeled for BrdU 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 BrdU-positive (BrdU+) intermediate cells in the stria did not differ significantly among the three groups. In contrast, there was a significant increase of BrdU + fibrocytes in the SL of furosemidetreated 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 furosemide 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.

Sox2 Up-regulation and Glial Cell Proliferation Following Degeneration of Spiral Ganglion Neurons in the Adult Mouse Inner Ear

“…12A, E). These results agree with previous observations on the proliferative activity of normal adult inner ear (Ruben 1967;Roberson and Rubel 1994;Yamashita et al 1999;Lang et al 2003). According to morphological characteristics, the BrdU + cells in the control ears are most likely the non-neuronal cells such as glial cells, fibroblasts, and vascular endothelial cells.…”

Divergent Aging Characteristics in CBA/J and CBA/CaJ Mouse Cochleae

“…Types I, II, and IV fibrocytes were assessed in the upper base using a 1,600 μm 2 area. These were identified based on location, an approach taken in previous studies (Hequembourg and Liberman 2001;Hirose and Liberman 2003;Lang et al 2003). Only nucleated profiles were included.…”

Chronic Reduction of Endocochlear Potential Reduces Auditory Nerve Activity: Further Confirmation of an Animal Model of Metabolic Presbyacusis

“…Pump implantation was similar to the procedures published previously Lang et al 2003). Animals were anesthetized with sodium pentobarbital (50 mg/kg) and were given atropine (0.2 mg/kg) to reduce respiratory secretions.…”