Microglial Activation and Noise-Induced Cognitive Vulnerability in a Chronic Hearing Loss Model
Bo Hyeon Park1, Jong Chan Jeon 1, Do Eun Kim 1, So Young Kim 1,2
1 Department of Anatomy and Cell Biology, Seoul National University College of Medicine, Seoul, Republic of Korea
2 Sensory Organ Research Institute, Seoul National University Medical Research Center, Seoul, Republic of Korea
Objective: This study investigated changes of microglial activity and cognitive function in chronic noise-induced hearing loss (NIHL). Methods: SD rats were exposed to 2–20 kHz white noise at 115 dB for 3 h/day for 5 days. Animals performed Novel Object Preference Test (NOPT) at three phases: pre-NIHL, post-NIHL, and post-NIHL with sound. Brains were collected for Ionized calcium-binding adaptor molecule 1 (Iba1) immunofluorescence staining, and microglial activation was assessed by cell counting and Sholl analysis. Results: In NOPT, NIHL models showed higher discrimination index (DI) at post-NIHL phase (p<0.001) but lower DI at post-NIHL with sound phase (p<0.001). Cell counting revealed that microglial numbers increased under sound exposure in both the auditory cortex (ACx) and hippocampus (HC) in control and NIHL models. The exacerbation observed in NIHL with sound exposure was accompanied with hippocampal morphological changes, including enlarged soma and reduced mean peak intersections (p<0.001; p=0.04). Conclusion: Chronic NIHL increases cognitive vulnerability under sound-exposed condition, accompanied with enhanced microglial activation.
