Reduced BDNF Expression in Auditory Cortex Contributed to Neonatal Pain Induced Hearing Impairment and Dendritic Pruning Deficiency in Mice

Abstract Hearing loss in children is common especially in NICU with consequences of worse outcomes in speech, language, education, social functioning, cognitive abilities, and quality of life. Whether neonatal pain is link to increase risks for hearing loss remains to be explored. Here, we implemented Complete Freund's adjuvant (CFA) plantar injection and needle prick model to mimic neonatal pain in NICU during critical period of hearing development. Auditory brainstem response (ABR) test was used to determine the hearing threshold at 4w and 8w postnatal. Sufentanil and Oxycodone were used as analgesic to treat neonatal pain. Hair cell and ribbon synapse stanning were performed to detect cochlear function. Golgi-cox staining and BDNF immunofluorescence of auditory cortex were performed to determine dendritic spine pruning in auditory cortex. The dendritic pruning related protein CaMKII and Rac1/2 level were detected by western blot. We found that CFA induced neonatal pain and ABR threshold increased at 4w and 8w postnatal and the impairment were attenuated after analgesic administration. Neither the inner hair cell (IHC) nor the synapse of CFA mice was damaged in cochlear. CFA mice showed increased dendritic spine density at auditory cortex and reduced BDNF level. Furthermore, Rac1/2 and CaMKII might contributed to the disrupt dendritic spine pruning. Our study suggested that neonatal pain could induced hearing impairment in adulthood ascribed to the reduced BDNF level and AC dendritic spine pruning deficiency, optimal analgesic in early-life could beneficial for hearing development.