Experimental Study Of The Effect Of Hyperbilirubinemia On Auditory System Function In Newborn Guinea Pigs

ObjectiveThis paper attempts to provide a solid prophase experimental research foundation for further studies,by exploring the responsibility of mismatch negativity (MMN) in guinea pigs,and the effect on the latency and amplitude of MMN in juvenile and adult guinea pigs,setting up an animal model of MMN recording techniques,and finding an objective measure system of the central auditory discrimination function.The paper also attempts to establish an easy-implementing the jaundiced animal model using newborn guinea pigs with hyperbilirubinemia to study the effect on auditory system function.It compares the effects on hearing function using different proportion of hyperbilirubinemia,by exploring the responsibilities of distortion product otoacoustic emission(DPOAE),auditory brainstem response(ABR) and MMN in guinea pigs with hyperbilirubinemia,and integrating with the observation of cochlear surface preparation and paraffin sections.MethodsTen normal juvenile and ten adult guinea pigs,obtained from laboratory animal center at Southern Medical University,were served as subjects.Each guinea pig was anesthetized via peritoneum injection and recorded MMN and ABR with passive mode.Four silver-wire pin electrodes were positioned in specific places of the skull. Acoustic stimuli were given in "oddall paradigm" pattern.The inducing rate,latency and amplitude of MMN which were elicited by 1000Hz frequency and 50dB SPL intensity were compared.We find an animal detection method about MMN and an objective measure of the central auditory discrimination function.Normal neonatal guinea pigs were randomly divided into three groups:control group,low-dose group and high-dose group.Based on the establishment of the jaundiced animal model,each guinea pig was scored by clinical symptoms on a scale described previously.DPOAE,ABR and MMN were tested respectively and the responsibilities of hearing tests were compared among three groups.Guinea pigs were euthanized with an overdose of Nembutal and perfused transcardially with a fixative solution containing 4%paraformaldehyde.The cochlear was captured by decapitation. After silver staining in basilar membrane and hematoxylin-eosin staining(HE staining) in cochlear paraffin sections,we observed three groups' injury situation of the inner and outer hair cells and inner ear structures by light microscope,especially the spiral ganglion and nerve fibers.ResultsWe established an animal detection method about MMN with passive mode, which consistents with requirements of detecting MMN and auditory discrimination function.The average latency of adult guinea pigs was shorter than that of juvenile guinea pigs when eliciting MMN by 1000Hz frequency and 50dB SPL intensity,and the difference was statistically significant(P=0.002,P=0.006).But there was no significant difference in amplitudes(P＞0.05).The latencies and amplitudes of MMN evoked by two stimulation modes showed no significant difference by paired-samples T test(P＞0.05).There was no significant difference between right ear and left ear (P＞0.05).There was no significant difference between two groups in latencies for waveⅠ,ⅢandⅤ,interwaves latenciesⅢ～Ⅴ,Ⅰ～Ⅴand the threshold of waveⅢ(P＞0.05),except for interwaves latencyⅠ～Ⅲ(t=2.12,P=0.04).After establishing the jaundiced animal models,the score about clinical symptoms showed significant difference among three groups(H=25.707,P= 0.000).The inducing rate and amplitude of DPOAE showed no significant difference among three groups(P＞0.05).But in ABR,the delayed latency of waveⅢand waveⅤand interwaves latencyⅠ～Ⅲshowed significant differences between low-dose group and control group(P＜0.05).All of above parameters of ABR showed significant difference between high-dose group and control group(P＜0.05).The inducing rates of MMN were significantly different among three groups (x~2=7.438,P=0.024).The average latency of control group was shorter than that of high-dose group,which was statistically significant(P＜0.05).However,the amplitudes of MMN showed no significant differences among three groups(P＞0.05). Inner and outer hair cells were observed with no obvious morphological changes by light microscope,and so were the spiral ganglion and nerve fibers.Conclusion1.An animal model of MMN recording technique is set up.MMN,as an objective measure of the central auditory discrimination function and central auditory development,provides a research foundation not only for related researches,but also for further studies and clinical application;2.A similar MMN exists in both guinea pigs and human beings,which has a process of development,differentiation and maturation according to the aging process. Therefore,guinea pigs can serve as the candidate animal for MMN research. Compared with ABR,MMN is more sensitive to evaluate the central auditory function;3.Hyperbilirubinemia can impair the information processing in auditory center and auditory discrimination of acoustic characteristics,such as frequency,intensity and duration.And it affects cognitive function,learning and memory induced by auditory;4.With the increased serum bilirubin levels,hyperbilirubinemia may not only cause obvious clinical symptoms,but also damage the central auditory system function,which can lead to sensorineural auditory functional disorder;5.The results of present study suggest that hyperbilirubinemia can impair the hearing function of auditory system,especially retrocochlear.However,the influence on cochlear and auditory cortex function may be slight.