Ken Kojima

Short duration high intensity sound (SDHIS) induced severe functional damage in adult rats.Previous reports showed that SDHIS induced severe histological changes in the cochleae of guinea pigs. This study examined the hearing functions of rats exposed to SDHIS.Animals were exposed for 1 min to a 137 dB sound pressure level (SPL) broadband noise. Auditory functions of the experimental animals were assessed using an auditory brainstem response (ABR) measurement system at frequencies of 8, 16, and 32 kHz before and 14 days after exposure to SDHIS.After SDHIS, none of the experimental animals showed any response when stimulated by maximum SPLs at all frequencies of our ABR system.

The mammalian inner ear derives from the otocyst. Molecular mechanisms underlying inner ear development are largely unknown. We have isolated a secreted molecule, OC29, from a rat otocyst cDNA library by the signal sequence trap method. OC29 was revealed to be a rat homologue of human WFIKKN. OC29 is preferentially expressed in the developing inner ear and the dorsal neural tube. In the inner ear, the expression of OC29 is first detectable at embryonic day 11.5 (E11.5), broadly in the dorsolateral region of the otocyst, which gives rise to the vestibular organ. At E12.5, the expression of OC29 becomes restricted to the presumptive sensory region, mainly to the BMP4‐positive presumptive cristae, and expression becomes reduced at later stages. These results suggest that OC29 may have a role in the early development of the inner ear sensory organ, particularly in the formation of the cristae of the semicircular canals. Developmental Dynamics 231:766–774, 2004.