Mechanisms Underlying Band-limited Noise Induced Plasticity In Young Auditory Cortex

The critical period, as defined by Kennard in 1938, is a developmental epoch during which sensory (environmental) experiences have major and long-lasting impacts on brain processing. These experience-dependent changes in the brain during critical period have been suggested to enable individuals to adapt to a wide range of environments.In the auditory cortex, for example, representations of spectral, temporal, and intensive of sound can be easily distorted by passive exposure to sound stimuli during the critical period. Recent studies in our laboratory, however, have shown that exposure of young rats to continuous broadband noise even after the critical period, induces critical-period-like changes in their primary auditory cortexes (AI). In this study, young rats at age of 8 weeks were exposed to continuous band-limited noise for six weeks. Expression levels and distributions of excitatory receptor subunits, inhibitory receptor subunits, BDNF, PV and GAD67 in the cortical field AI were then examined by using immunofluorescence techniques, to explore the mechanisms underlying the noise induced cortical changes in these young rats. The results showed that 1) the expression of AMPAR subunit GluR2 in cortical area covered by spectrum of the band-limited noise increased when compared to CON, which, however, was decreased comparable to that of JUV; 2) the expression of NMDARs subunit NR2B in cortical area covered by spectrum of the band-limited noise decreased (particularly in the cortical layers Ⅱ-Ⅲ、Ⅳ and Ⅵ) but with no noticeable change in the expression of NR2A; 3) the expression levels of GABAAR subunit β1/2/3 decreased in cortical area covered by spectrum of the band-limited noise. That of α1, however, only decreased in the cortical layer Ⅵ; 4) both expressions of PV and BDNF in cortical area covered by spectrum of the band-limited noise decreased compared to CON. These studies indicate that changes in expression balance of excitatory and inhibitory receptors and that in BDNF, PV and GAD67 play critical roles in observed cortical plasticity in young rats induced by continuous band-limited noise after critical period.