Effect Of Early Acoustic Experience On The Development Of Auditory Function In Central Auditory System And The Underlying Mechanism

Sensory experiences have important roles in the functional development of the mammalian auditory cortex.In our present study,we investigated the effects of early auditory experience on rat auditory function and the underlying mechanism.Out study is divided into four parts.1.The effect of early continuous white noise exposure on auditory azimuth sensitivity of A1 neurons.By rearing infant rat pups under conditions of continuous,moderate-level white noise,we found that noise rearing markedly attenuated the spatial sensitivity of A1 neurons.Compared with rats reared under normal conditions, spike counts of A1 neurons were more poorly modulated by changes in stimulus location and their preferred locations were distributed over a larger area.2.The effect of early continuous white noise exposure on expression of GAD65,GABA_A receptor subunits,AMPA receptor GluR2 subunit,and NMDA receptor subunits in rat auditory cortex.By rearing infant rat pups under conditions of continuous,moderate-level white noise,we found that early continuous noise rearing induced significant decreases in AMPAR GluR2 subunit expression,GAD 65 and GABA_A receptorα1 subunit expression,and an increase in GABA_A receptorα3 expression, which indicates a returned to the juvenile form of GABA_A receptor,with no effect on the expression of N-methyI-D-aspartate receptors(NMDARs).These observations indicate that noise rearing has powerful adverse effects on the maturation of balance between cortical inhibition and excitation,which might be responsible for the reduced spatial sensitivity.3.The effect of early continuous white noise exposure on expression of GAD65,GABA_A receptor subunits,AMPA receptor GluR2 subunit,and NMDA receptor subunits in rat inferior colliculus. By rearing infant rat pups under conditions of continuous,moderate-level white noise,we found that early continuous noise rearing induced significant decreases in AMPAR GluR2 subunit expression,GAD 65 and GABA_A receptorβ3 subunit expression,with no effect on the expression of GABA_ARα1,α3 subunits,and N-methyI-D-aspartate receptors(NMDARs).4.Early auditory enrichment with music enhances auditory discrimination learning and alters NR2B protein expression in rat auditory cortexIn our present study,we investigated the effects of early auditory enrichment with music on rat auditory discrimination learning.We found that early auditory enrichment with music from postnatal day(PND) 14 enhanced learning ability in auditory signal-detection task and in sound duration-discrimination task.In parallel,a significant increase was noted in NMDA receptor subunit NR2B protein expression in the auditory cortex. Furthermore,we found that auditory enrichment with music starting from PND 28 or 56 did not influence NR2B expression in the auditory cortex.No difference was found in the NR2B expression in the inferior colliculus(IC) between music-exposed and normal rats,regardless of when the auditory enrichment with music was initiated.Our findings suggest that early auditory enrichment with music influences NMDA-mediated neural plasticity,which results in enhanced auditory discrimination learning.