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Dominant white spotting W/W(v) and W(v)/W(v) mice are well-known mutants that lack strial intermediate cells in their cochlea and manifest hereditary sensorineural hearing loss. We recently reported marked thickening of and IgG deposition on the basement membrane of strial capillaries in W/W(v) mutant mice, similar to observations made in aged animals and in animals with autoimmune sensorineural hearing loss. The present study aimed to clarify the age-dependent changes in these pathological findings of strial capillaries in the W/W(v) mice. Male WBB6F1 +/+ and dominant white spotting W/W(v) mutant mice were sacrificed by transcardiac perfusion with paraformaldehyde solution. The cochlear ducts were isolated and subjected to light- and electron-microscopy, immunohistochemistry, immunoelectron microscopy. Alternatively, lanthanum chloride tracer examination in the isolated cochlear ducts was performed in order to compare the permeability of the strial capillaries between +/+ and W/W(v) mice. In the W/W(v) mice, thickening of and IgG deposition on the basement membrane of strial capillaries were observed as early as 1 week after birth and became more noticeable with age. Deposited IgG was preferentially localized to the thickened basement membrane and was also observed in partially the intercellular space between adjacent of endothelial cells. In addition, pinocytotic vesicles both in the apical and basal lesions of such cells also showed IgG deposition. Lanthanum chloride was retained along apical plasma membrane of the endothelial cells in the +/+ mice but penetrated through the endothelial layer in the W/W(v) mice. These results indicate that active transport via pinocytotic vesicles as well as increased permeability of strial capillaries in the W/W(v) mice occur in the early stage after birth, resulting in the morphological alterations in the strial capillaries of these mice.

This study attempts to investigate the development of sensorineural hearing loss following a head blow without skull fracture in association with physiological and histopathologic changes in an experimental animal model. With the head in a freely movable position, albino guinea pigs were given a single blow to the occipital region by a head blow device. At 1, 7, and 14 days after the blow, the animals' auditory brainstem response (ABR) and cochlear microphonics (CM) were examined, and both the temporal bone and brain stem were observed by light and electron microscopy. The ABR threshold was unchanged at day 1, was significantly increased at day 7, and was fully recovered at day 14. The I-V and I-II interpeak latencies were significantly prolonged at days 1 and 7, and wave I latency was significantly prolonged at day 7 only. These latencies were recovered to normal limits at day 14. On the other hand, no significant change in CM versus the control group was observed at any point in the measurements. Histopathologically, no abnormal finding was seen at the light microscopic level. However, at the electron microscopic level, there were some injuries to the eighth nerve. At day 1, the lamellar structure of the myelin sheath was irregular, and the periaxonal space was expanded; at day 7, the myelin sheath was disintegrated. At day 14, however, these changes were partially reversed. These results suggest that sensorineural hearing loss following a head blow in this model is attributed to dysfunction of the eighth nerve rather than to cochlear impairment.