| Using Elvax chronic releasing method, multicolor fluorescence in situ hybridization (McFISH), electrophysiological and behavioral methods, we studied the role of NMDA receptor in experience-dependent auditory developmental plasticity on early auditory experience experimental animal model at levels of receptor, molecular, cell and system, with animals' auditory spatial azimuth discriminating ability, auditory spatial orientation sensitivity of auditory neurons and the change in components/ratio of NMDA receptor subunits mRNAs expression as indexes, giving experimental evidence to determine mechanisms of brain functional developmental plasticity.The first part of this paper focused on the effects of early auditory experience on animal's auditory functional development, with the main contents as followed:1. Effects of auditory experience on auditory spatial discrimination behavior in rats of different postnatal-week ageThe auditory spatial discrimination ability of different animal groups were investigated in detail during the pre-foundation stage, post-foundation stage and fadeaway stage of sound-alimental conditional reflex in 24 SD rats. The results indicated the experience-dependent changes in animals' auditory spatial discrimination behavior caused by training with short-duration pure-tune of 3kHz at the right 45?azimuth in front of animals during postnatal developmental critical period, which were demonstrated by the significant preference to 3kHz sound of right 45? the shortened course needed in foundation of 45?orientation conditional reflex, the shorter mean reaction time, smaller orientation error, improved response success rate and the prolonged course needed in the orientation reflex fading-away. The results suggests that early postnatal experience cause the experience-dependent changes in auditory behavior of rats.2. Effects of auditory experience on response properties of neurons in auditory cortex in animals of different postnatal-week ageData obtained from 32 SD rats revealed that early auditory experience induced experience-dependent changes in response properties of auditory cortex neurons. Compared with normal group, the amount of 3 kHz-BF neurons became larger, response centers centralized to 45?in auditory space, with the sharper frequency tuning curves, lower threshold and larger QndB value. This trend displayed above was in accordance with the behavioral tests, suggesting that auditory experience in developmental critical periodwould improve the auditory spatial orientation sensitivity of neurons in auditory cortex AI area.3. Effects of auditory experience on space-time expression of NMDA receptor subunits mRNAs in auditory cortex in animals of different postnatal-week ageBy multicolor fluorescence in situ hybridization method, our research determined the changes in density and components/ratio of NMDARs single-labeled, double-label -ed and multi-labeled positive neurons in bilateral auditory cortex of auditory experienced animals of postnatal week (PNW) 3, 5 and 8, and found an unevenly increasing trend compared with normal group, with the change in PNW 3 especially larger. It means early auditory experience changed the expression of NMDARs mRNA, accordant with the results of electrophysiological and behavioral experiments, suggesting NMDA receptor play an important role in experience-dependent brain functional developmental plasticity.The second part of the paper studied the functional significance of NMDA receptor in auditory developmental plasticity after chronically blocking NMDARs expression in unilateral auditory cortex during animals' postnatal developmental critical period through Elvax-loaded drug chronic releasing technique. Followed are the main contents:1. Effects of NMDA receptor antagonist on experience-dependent auditory spatial discrimination behaviorThe auditory spatial discrimination behavior of drug-implanted group and control group at different PNW were investigated during the pre-foundation stage, post-foundation stage and fadeawa...
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