Experimental Study Of NNOS And INOS On Cochlea Injury In Newborn Rats Of Hypoxia-ischemia

Background and objectives: Hypoxic-ischemic encephalopathy (HIE) is a disorder of cerebral trauma in perinatal neonates. The survival of HIE will have neuronal sequela, the important one of which is sensorineural deafness. In recent years, study about HIE deals with a lot of fields, and people pay more and more close attention to the effect of NO in HIE and reports are increasing. NO is a kind of gas neurotransmitter and transfers information among cells. It has been approved that NO exert double effects. The shred release of NO transfers information messenger and exerts important effect in physiology condition. Hypoxia-ischemia will lead to a great deal of release of NO and then NO exerts powerful cell toxicity. In body, nitric oxide synthase (NOS) can reflect the level of NO, which is the restriction enzyme of NO synthesise. Now, people have make great progress about physiology of NO and NOS, but study about hearing is beginning and people are short of pathology and even animal models. Study of NO and NOS about cochlea injury in newborn rats of hypoxia-ischemia does not report. To investigate the roles of NO and NOS of HIE, this research measured ABR and AP and used the technology of immunohistochemistry to observe the changes of nNOS and iNOS. The study will try to detect if NO and NOS will exert effect in HIE. The researcher believes that to detect hearing loss after hypoxia-ischemia must benefit for the prevention and therapy of HIE.Materials and Methods:1. Seventy-two healthy Wistar rats of 7 days old, weighted from 9 to 20 g, not used ototoxicity drug, were randomly assigned to 5 groups (n=12): the normal control group, the sham operation group, hypoxia-ischemia 6h group, hypoxia-ischemia 12hgroup and hypoxia-ischemia 48h group.2. To make the HIE model: Ligate left common carotid artery (LCCA) and then the rats were laid in the room including of 5% O2 and 95% Na. Successful model of HIE must be proved by pathology. The normal control group was not being dealed with anything and the sham operation group only separated LCCA.3. The animals in each groups were examined the auditory brain response (ABR) thresholds, the latencies of wave I , II, III and the interwave latencies of II -III, and AP N1 thresholds and the latencies. The intensity of ABR and AP began with 90dB and reduced to disappearing of wave II . Statistical analysis was performed with SPSS 10.0 soft. Statistically significant level was considered as "alpha equals 0.05".4. Just the final examination of ABR and AP, endocardial perfusion were completed, the skull was opened. Then the brain and cochlea were removed. Slices of the brains and one part of slices of the cochleas were stained with HE. Others of the cochleas were studied by nNOS and iNOS immunohistochemistry staining respectively. The study used the HPIAS-1000 image-quantities analysis system to exam the average gray value of production of nNOS and iNOS positive reactivity. Statistical analysis was performed with SPSS 10.0 soft. Statistically significant level was considered as "alpha equals 0.05".Results:1 . The normal control group and the sham operation group had little change about the thresholds of ABR and AP, the latencies of wave I , II, III, and the interwave latencies of II -III and AP N1 (P>0.05). But the hypoxia-ischemia groups and the normal control group had oblivious changes (P<0.05).2. In the hypoxia-ischemia groups, the neurons decreased and were swelling, and the quantities of Nissl bodies decreased. But the normal control group was reverse.3. In the normal control group outer hair cells (OHC) ranged in order. In the hypoxia-ischemia 6h group OHC disarrayed and they became worse and stria vascularis (SV) was becoming thinner in the hypoxia-ischemia 12h and 48h groups. But inner hair cell (IHC) and tectorial membrane (TM) were normal.4. The quantities of nNOS and iNOS increased obviously in the cochlea of HIE rats. And the expression of nNOS and iNOS was the intensest early and late respectively. The image-quantity analysis indicated that...