Hearing impairment in WBN/Kob rats with spontaneous diabetes mellitus

Abstract

SummaryThe inner ear of spontaneously diabetic WBN/Kob rats was functionally and morphologically examined in order to elucidate the relationship between diabetes mellitus and hearing impairment. At 3 months of age, WBN/Kob rats were non-diabetic, and their hearing function was normal. At 6-7 months of age, they showed decreased glucose tolerance and an increasing tendency toward urinary excretion of glucose without high plasma concentration of glucose, and were therefore judged to be pre-diabetic. They also displayed a significant elevation of hearing threshold in the auditory brainstem response, but showed little morphological and histochemical changes in the inner ear. At 12-13 months of age, they were spontaneously diabetic and showed a more apparent elevation of hearing threshold in auditory brainstem response than that in pre-diabetic animals. In addition, they displayed a marked decrease in the number of spiral ganglion cells and oedematous changes in the stria vascularis. The stria vascularis also showed a decrease in the intensity of staining with some lectins, i.e., wheat germ agglutinin, succinylated wheat germ agglutinin, Soranum tuberosum lectin, and concanavalin A. In conclusion, hearing impairment is induced by diabetes in the WBN/ Kob rats first as an elevation of hearing threshold along with glucose intolerance; secondly, as a decrease in the number of spiral ganglion cells; and thirdly, as oedematous change of the stria vascularis with decreased intensity of lectin staining. [Diabetologia (1995) tional and morphological examinations simultaneously on human subjects. However, we studied WBN/Kob rats which are derived from Wistar rats [14] and develop diabetes spontaneously due to endocrine-exocrine pancreatic insufficiency [15][16][17][18][19]. They begin to excrete odorous urine abundantly at the age of about 9 months, and thereafter show hyperglycaemia and marked intolerance to glucose. Since they can survive for a long time after the onset of diabetes without insulin treatment, they are a pertinent animal model for analysis of various aspects of diabetes [20,21]. In the present study, therefore, male WBN/Kob rats with spontaneous diabetes underwent functional, morphological, and histochemical examinations to determine the effects of diabetes on auditory function.

Increased Inner Ear Susceptibility to Noise Injury in Mice With Streptozotocin-Induced Diabetes

“…This was as expected because the C57BL/6 mice used in the current study are well-known to develop sensorineural hearing loss much earlier in life than other mice (33–35). However, no significant differences in aging-related hearing impairment were observed between the diabetic and control mice, in accordance with a previous study using the STZ-induced diabetes model in CBA/CaJ mice (20) but in contrast with findings from the rat model of chronic pancreatitis and spontaneous diabetes (19). Most interestingly, we showed that recovery from noise-induced injury was significantly impaired in an experimental diabetes model, consistent with a previous report using the STZ-induced diabetes rat model (21).…”

“…A longitudinal study on diabetic rats (WBN/Kob) showed hearing impairment compared with age-matched Wistar rats (19). In middle-aged mice, type 2 diabetes induced by a high-fat diet led to significant hearing impairment over a period of 6 months.…”

“…Morphologically, loss of OHCs (19,22–25) and inner hair cells (IHCs) (22) has been reported in diabetic rodent models. Changes in intermediate and marginal cells of the stria vascularis (19,22,23), degeneration of spiral ganglion cells (SGCs) (19,25), and thickening of the basement membranes of capillaries in the stria vascularis (26) have also been reported.…”

“…Changes in intermediate and marginal cells of the stria vascularis (19,22,23), degeneration of spiral ganglion cells (SGCs) (19,25), and thickening of the basement membranes of capillaries in the stria vascularis (26) have also been reported. However, another study did not find any of these changes in diabetic rats (27).…”

Adiponectin deficiency exacerbates age-related hearing impairment

“…9 A diabetic condition generated by streptozotocin injection or a high-fat diet also leads to exacerbation of hearing loss in aged mice. 10, 11 In contrast, it has been shown that caloric restriction slows the progression of ARHI in various strains of mice. 12, 13 These data suggest that metabolic dysfunction under conditions of obesity is causally linked to the development of ARHI.…”