Decreasing auditory input induces neurogenesis impairment in the hippocampus

Hearing loss is associated with cognitive decline and dementia risk. Sensorineural hearing loss suppresses hippocampal neurogenesis, resulting in cognitive decline. However, the underlying mechanism of impaired neurogenesis and the role of microglial activation and stress responses related to hearing loss in the hippocampus remains unknown. Using a conductive hearing loss (CHL) model, we investigated whether a decrease in sound level could induce impairment of hippocampal neurogenesis and examined the differences between unilateral CHL (uCHL) and bilateral CHL (bCHL). To establish the CHL mouse model, ears were unilaterally or bilaterally occluded for five weeks by auditory canal ligation. Although hearing thresholds were significantly increased following CHL, CHL mice exhibited no significant loss of spiral ganglion or hippocampal neurons. Hippocampal neurogenesis was significantly and equally decreased in both sides following uCHL. More severe decreases in hippocampal neurogenesis were observed in both sides in bCHL mice compared with that in uCHL mice. Furthermore, microglial invasion significantly increased following CHL. Serum cortisol levels, which indicate stress response, significantly increased following bCHL. Therefore, auditory deprivation could lead to increased microglial invasion and stress responses and might be a risk factor for hippocampal neurogenesis impairment.

Automated summary

The study found that sensorineural hearing loss, which causes hearing decline, suppresses hippocampal neurogenesis leading to cognitive decline. Using a CHL model, it was observed that both unilateral and bilateral CHL significantly decreased hippocampal neurogenesis, with more severe reduction in hippocampal neurogenesis in bilateral CHL compared to unilateral CHL. Additionally, microglial invasion and stress responses increased following CHL, suggesting auditory deprivation may be a risk factor for impaired hippocampal neurogenesis.