Evaluation of the Effects of Chronic Injection of D-Galactose on Auditory Brainstem Responses as a Model for Studying Age-Related Hearing Loss

The D-galactose induced mimetic aging rat model has been widely used in studies of age-associated diseases recently. Evidence indicates that D-GAL could also play a key role in age-related hearing loss. However, there is conflicting data about the relationship between the D-GAL injection and tone-burst auditory brainstem responses (ABRs). The present study aimed to compare ABRs in D-GAL injected rats compared with young and naturally aged rats. Tone-burst ABR was recorded and analyzed at the frequencies of 4,6,8,12 and 16 kHz in male young (3-month-old, n=10), naturally aging (18-month-old, n=10) and D-GAL injected (3-month-old, 500 mg/kg D-GAL injection for 8 weeks, n=10) Wistar rats. When the ABRs thresholds obtained in the D-GAL group and the natural aging group were compared with the thresholds in the young group, we observed a significant increase in thresholds, which affected all of the frequencies (P<0.05). A statistically significant decrease in amplitude of wave PI at 4 and 8 kHz, PII at 4,8 kHz, PIV at 4,6,8,12 and 16 kHz was also observed in naturally aging group compared with young group. However, in D-GAL group, a significant difference was exclusively detected in amplitude of PIII at 4 kHz. Latency did not reveal any significant difference between the groups (P>0.05). The present study confirmed that experimental injection of 500 mg/kg/day D-GAL for 8 weeks to Wistar rats could lead to ABRs threshold shifts but not latency. Because there are several types of presbycusis, further studies are needed to determine what type of presbycusis is induced by D-GAL and where is the first region affected by it to provide the best treatment and prevention methods.