Kentaro Ashida

Hair cell regeneration in the chick inner ear following acoustic trauma: ultrastructural and immunohistochemical studies

The regeneration of hair cells in the chick inner ear following acoustic trauma was examined using transmission electron microscopy. In addition, the localization of proliferation cell nuclear antigen (PCNA) and basic fibroblast growth factor (b-FGF) was demonstrated immunohistochemically. The auditory sensory epithelium of the normal chick consists of short and tall hair cells and supporting cells. Immediately after noise exposure to a 1500-Hz pure tone at a sound pressure level of 120 decibels for 48 h, all the short hair cells disappeared in the middle region of the auditory epithelium. Twelve hours to 1 day after exposure, mitotic cells, binucleate cells and PCNA-positive supporting cells were observed, and b-FGF immunoreactivity was shown in the supporting cells and glial cells near the habenula perforata. Spindle-shaped hair cells with immature stereocilia and a kinocilium appeared 3 days after exposure; these cells had synaptic connections with the newly developed nerve endings. The spindle-shaped hair cell is considered to be a transitional cell in the lineage of the supporting cell to the mature short hair cell. These results indicate that, after acoustic trauma, the supporting cells divide and differentiate into new short hair cells via spindle-shaped hair cells. Furthermore, it is suggested that b-FGF is related to the proliferation of the supporting cells and the extension of the nerve fibers.

Regeneration of Adult Budgerigar’s Hair Cells following Acoustic Trauma

The functional and structural changes of hair cells of the adult budgerigar following acoustic trauma were examined using auditory brainstem response (ABR), and both scanning and transmission electron microscopy. Just after exposure to a 1,500-Hz pure tone at 120 dBSPL for 98 h, severe damages and disappearance of short hair cells were observed in the middle region of the basilar papilla. Fourteen days after the exposure, the threshold of ABR recovered to the level before the exposure, and normal short hair cells, which have synapses with nerve endings, were rearranged all over the damaged region of the basilar papilla. These results indicate that the hair cells of the adult budgerigar have capability to regenerate, and to restore the auditory perceptive function following acoustic trauma.

The Ultrastructure of the Basilar Papilla of the Budgerigar's Inner Ear

The basilar papilla in the inner ear of the adult budgerigar was studied by scanning and transmission electron microscopy. The sickle-shaped basilar papilla has short hair bundles on the proximal tip and long ones on the distal tip. The tectorial membrane shows a honeycomb-like pattern and enclosed a hair bundle in its alveolus. The papilla consists of two different types of hair cells; short and tall hair cells. The short hair cells with large efferent nerve endings are located on the free basilar membrane in the inferior part. The tall hair cells with large afferent nerve endings are located in the superior part. The similarity and difference of the structure are discussed between the budgerigar and other birds, and between birds and mammals.

Glossopharyngeal Neurinoma Causing Hearing Loss and Tinnitus; A Case Report.

A 31-year-old man visited us complaining of hearing loss and right ear tinnitus. Pure tone audiometry showed moderate sensorineural hearing loss with poor speech discrimination. Ear X-ray was normal. ABR revealed no response except wave-I. MRI clearly demonstrated a spaceoccupying lesion in the right cerebello-pontine angle ; it showed a low intensity signal in the Ti-weighted picture and a high intensity signal in the gadoliniumenhanced picture.A posterior fossa craniotomy revealed a partially cystic tumor arising from the ninth cranial nerve. Subtotal removal of the tumor was performed, leaving the 10th, 11th and 12th cranial nerves intact. After operation, pure tone audiometry and ABR results became normal.

Electrocochleography of Vestibular Meniere's Disease

Clinical vestibular and auditory studies were done on 17 patients with vestibular Menieres disease characterized by recurrent episodes of vertigo. According to the duration of the vertigo attack, the subjects were dividided into two groups. Four of eight patients in the group with long duration of vertigo (more than 10 minutes) showed fluctuating hearing loss in the lower frequency ranges and later develo ped typical Menieres disease. All of them exhibited canal paresis and three of them have predominance of -SP in the affected ear. We concluded that in patients with vestibular Menieres disease with long vertigo attacks and predominance of -SP and canal paresis, vestibular symptoms would probably be followed by the development of typical Menieres disease.