-This study was designed to evaluate changes in auditory brainstem response (ABR) in the course of auditory disturbance in rats induced by Kanamycin (KM). KM was administered subcutaneously to 12 CD (SD) male rats aged 6 weeks for 10 days at a dose of 800 mg/kg. Death was observed in one male on day 8 and 2 males on day 10. It was thought that kidney damage was the cause of death from histopathological findings. ABR was recorded before KM treatment and on days 4, 8, 10 and 11 after KM treatment. The ABR changes after KM treatment in rats were as follows. On day 4, 6 rats showed an increase in amplitude of waves I and/or II and on day 8, among those, 4 rats still showed a high amplitude of waves I and/or II. On day 8, 2 rats showed an elevation of ABR threshold (15-40 dB SPL) and a decrease in amplitude of wave I and increase in amplitude of wave II at the same time. On day 11, 7 rats showed a decrease in amplitude of wave I. In addition, ABR threshold shifts 10-70 dB SPL were observed in those rats. In ABR recording, KM-induced auditory disturbance model rats showed an increase in amplitude of waves I and/or II earlier than an ABR threshold shift. By analyzing temporal alteration of amplitude of the ABR components, we could detect precursory phenomenon of the auditory disturbance at an early phase of treatment. By following the pathway of click-ABR and tone pip-ABR examination, the auditory disturbance of low-frequency to high-frequency range could be analyzed at an early date in detail.

SummaryUnilateral (left eye) optic nerve hypoplasia was detected in a six-month-old male Beagle dog. Vision testing indicated that the left eye had poor vision and testing the pupillary light reflex showed the left eye to have an absence of the afferent pathway of the reflex but it had a normal efferent pathway. Ophthalmoscopy revealed a small-sized optic disc, winding retinal artery and dilated retinal vasculature in the left globe. Electroretinography showed no abnormal findings even in the left globe. Histopathologically, the left optic nerve was markedly hypoplastic and was composed of sparse neural elements and a moderate amount of connective and glial tissues. In the retina of the left globe, the nerve fibre layer and the ganglion cell layer were reduced in thickness, although a small number of ganglion cells were still present. There were no abnormal findings detected in the right globe and the right optic nerve. The brain appeared normal macroscopically.