The Changes Of Auditory Brainstem Nuclei And Their Glutamic Acid Decarboxylase In The Aged Rat

Objectives:Presbycusis is a normal aged disease.lt is also one of the mostcommon hearing dysfunctions in old people.But the mechanism of presbycusis is not completely clear.The recent study indicated that old people's hearing loss is dued to the changes of terminal organ and brainstem. Neurotransmitters are involved in both of the two kinds of changes. They play an important role in the process of hearing signal being transmitted.The balance of excited and inhibitory neurotransmitters in neural system may guarantee hearing signal to be transmitted correctly.Once neurotransmitters change,the transmittance of hearing signal will be affected. Gamma-aminobytric acid(GABA)is a major inhibitory neurotransmitter in the central neural system of mammalian.In the auditory system,GABA plays neural inhibition role through combining with its corresponding receptor.So that it can inhibit endogenous and exogenous noise,and improve hearing and speech discrimination.GABA is produced through glutamate.Glutamic acid decarboxylase(GAD) is its limited enzyme.In the central neural system,GAD has two forms,GAD65 and GAD67.Research showed there are GABA and GAD immunoreactive positive neurons and terminals in auditory brainstem nuclei.On physiological conditions,the organism may compose certainly quantative GABA,its function is maintaining neural impulse to be conducted correctly.However,on pathological conditions,many factors may affect the product and activity of GAD.This will affect the synthesis of GABA and make neural impulse can't be conducted correctly. Combining with old people's poor speech discrimination and their reduction in inhibiting the stimulate of sound,especially in the presence of background noise,we deduce that the changes ofGABA in auditory brainstem nuclei may play some role in the mechanism of presbycusis.But,at present,the study on presbycusis is mainly concentrated on cochlea,the auditory center is little concerned.The research on whether GAD changes in auditory brainstem nuclei is less.In order to further discuss the role of auditory brainstem nuclei and GABA in the mechanism of presbycusis,this research used toluidine blue staining and the technology of immunohistochemistry to observe the changes of auditory brainstem nuclei and GAD65 and GAD67 in auditory brainstem nuclei in aged rat caused by D-galactose and analyse the reason.So that we provide theorectical basis for the prevention and therapy of presbycusis in clinic.Materials and Methods:1.Rats were used in this study.Sixty healthy Wistar ratswith sensitive ear reflection were randomly divided into two groups:an experimental group and a control group.Each group consisted of 30 rats.The experimental group was treated with ip injections of D-galactose for six consecutive weeks,in a daily dosage of 50mg/kg.The control group was received the same dosage of normal saline per day ip for six consecutive weeks.2.The animals in each group were examined the auditory brain response(ABR) thresholds,the latencies of wave I,IH,V and the interwave latencies of I-III,III-V,I-V.3.In addition,the vitality of superoxide dismutas(SOD) and the density of MDA in serum were measured.4.Just the final examination of ABR was completed,the chest was opened and 150-200ml normal saline was used to wash away the blood through the left ventricle rapidly.Soon after this,500ml 4% polyformaldehyde phosphate buffer(PH7.4)was used to perfused slowly.Then the skull was opened and the brain was removed and laid in the above buffer. The specimen was sheared the next day and the brainstem was placed into the same liquid to be fixed for a week.Finally,the specimen was embeded by paraffin and was sliced successively.4 parts of slices in each specific position were taken.These positions were cochlear nuclei,superior olivary complex,nuclei of the lateral lemniscus and inferior colliculus.One part of slices were stained with toluidine blue.Two parts of slices were studied by GAD65 and GAD67 immunohistochemistry staining respectively.The other part of slices were used to be negative c...