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Objective: To measure the cochlear compound action potential (CAP) and the densities of hair cells (HCs) along the whole length of the basilar membrane (BM) in adult chinchillas. And to investigate the relationship between the severity of inner hair cells (IHCs) loss and the changes of CAP by using carboplatin-cochlear lesion model. Methods: Totally 18 chinchillas were recruited after ontological evaluation. They were randomly divided into three groups (with 6 subjects in each), A: control, B and C: legion groups treated with one or two shot(s) of carboplatin respectively (76 mg/kg in one shot, i.p., one-week interval between the two shots). Endpoint tests were performed 30 days after the carboplatin treatment in groups B and C, and matched time in group A. A sliver-ball electrode was placed into round window niche via hypotympanic approach in anesthetized chinchilla. CAP was measured in response to clicks and tone burst of 0.5, 1, 2, 4, 8, 16 kHz respectively under anesthesia. CAP amplitudes and thresholds were measured and compared across the groups. After the recording, the whole cochlea surface preparation was made and the HCs were stained in histochemistry against substrate of succinate dehydrogenase (SDH). Images were taken with high-resolution digital camera under light microscope and across the whole cochlea. The length of the basilar membrane (BM) and the number of both IHCs and OHCs were counted. The HC density was calculated as the number of HCs per 10% BM length. Results: The CAP thresholds were (7.1±2.6), (25.4±5.0), (24.6±5.4), (10.4±5.0), (0.4±1.4), (4.2±6.3) and (17.1±14.1) dB SPL (from 6 subjects in group A, n= 12 ears) corresponding to stimuli of Click and 0.5, 1, 2, 4, 8, 16 kHz tone bursts respectively. The total number of cochlear HCs were measured as (8 936±643) ( x ± s ) and the average length of the BMs was (17.73±1.012) mm from the six subjects in the group A ( n= 12 ears). The HC density was found to be varied slightly across the BM. There was no significant CAP threshold difference between the control (group A) and the group B, which received one shot of carboplatin. However, the maximal CAP amplitude was reduced by 40% in the group B and compared with group A. Correspondingly, approximately 40% loss of IHCs were seen. In contrast, a significant CAP threshold shift was seen in subjects receiving two shots of carboplatin (group C), which was accompanied by a loss of 90% IHCs. Conclusions: The CAP thresholds of adult chinchillas show typical open-V shape with the lowest values at 2, 4, and 8 kHz. IHC loss by carboplatin in certain degree is well correlated with CAP amplitude reduction, but does not change the threshold when inner hair cell loss reaches 40%, however, if inner hair cell loss exceeds 80%, the threshold shift of CAP will be inevitable.

Objective: In order to observe the action of H2O2 on inner and outer hair cells of organ of Corti in mouse, and discuss whether Tiron can effectively resistant the injury of free radicals in cultured cochlea in vitro or not., Method: Using the culture technology of organ of Corti in newborn mouse in vitro, established the model of the injury of inner and outer hair cells caused by exogenous H2O2. And observed the protection to the damage by H2O2 at different concentration of Tiron., Result: When the concentration of H2O2 is higher than 1.0 mmol/L, the loss of hair cells in the bottom, middle, and parietal turn of basilar membrane vary, the injury of bottom turn is more severe. In lower than 0.5 mmol/L group, the injury of hair cells is no relationship with the location. Adding Tiron (10 mmol/L) in culture can apparently decrease the injury of hair cells caused by H2O2. When the concentration of H2O2 is 0.01-1.0 mmol/L, Tiron can almost inhibit the loss of hair cells completely., Conclusion: There is apparently preventive effection of Tiron on organ of Corti cultured in vitro, and the mechanism of inhibiting injury caused by H2O2 is probably by clearing O2- and combining irony ion.

Objective: This paper describes a convenient histochemical technique that allows one to simultaneously assess the cochlear efferent neurons and inner (IHCs) and outer hair cells (OHCs)., Method: Selective labeling of the sensory cells and efferent fibers was carried out by first labeling the hair cells for dehydrogenase activity and then staining the efferent fibers for acetylcholinesterase activity. Double-labeled specimens were prepared as a surface preparation and counts were made of the number of hair cells and the number of discreate fiber bundles crossing the tunnel of Corti along the entire length of the cochlea., Result: The utility of this technique for assessing ototoxic damage was demonstrated by constructing cochleograms showing the percentage of missing hair cells and tunnel-crossing efferent fibers in chinchillas treated with carboplatin. In the region of the cochlea associated with most IHC loss and a part of OHC missing showed by succinate dehydrogenase in the region of hair cells; however, the loss of tunnel-crossing efferent fibers showed by acetylcholinesterase staining was closely correlated with the percentage of OHC loss. But, if only damage the IHC, the efferent fibers showed normal., Conclusion: These results suggest that carboplatin damaged efferent systems may be due to the damage of OHC.

Objective: To introduce a method of chronic infusion of drugs into the cochlea using a osmotic pump., Methods: A stainless steel tube was surgically implanted into the basal turn of the chinchilla cochlea and connected to the pump. To assess the reliability of the procedure, and the pump, Hank's solution or L-buthionine-[S,R]-sulfoximine (BSO) was infused into the cochlea by this pump and inferior colliculus (IC) potential and hair cell morphology were examined., Results: In three Hank's solution infused cochleas, the thresholds of IC potential were kept in the normal level and no hair cell loss was found 14 days after the beginning of the infusion, suggested that the pump implantation and Hank's solution infusion had no significant effects on the cochlear functions. In contrast, threshold shifts of IC potentials and hair cell loss were found in two BSO infused animals, suggested that the infused solution had distributed into the whole cochlea., Conclusion: This study indicates that the osmotic pump can be used in chronic delivery of experimental drugs into the cochlea.