some normal level of expression for each gene examined. In exposed animals, most glycine receptor subunits showed a trend towards an initial increase in expression followed by a decline in gene expressi- on; however only glyR2a showed statistically significant increases in expression at the 0 (p ≤ 0.035) and 5 (p ≤ 0.020) day time points with a return to normal expression levels by 29 days. A similar trend was seen among muscarinic receptors with increased expression immediately after exposure, followed by decreased expression at later time points. Again, only one of the receptors showed a statistically signi- ficant change in expression with muscR4 having decreased levels two (p ≤ 0.025) and five (p ≤ 0.033) days after exposure. Compared with agematched controls, ChAT expression after noise exposure sho- wed a different temporal pattern from those of glycine and muscarinic receptors, with no change in gene expression at the 0 day time point, a sustained increase in expression that was statistically significant by the 14 day time point (p ≤ 0.038) and a 65% decrease in expression at the 29 day time point (p ≤ 0.084). These results suggest that alterations in the expression of neurotransmitter receptors influencing inhi- bition are among the changes occurring in the DCN that are thought to underlie noise-induced tinnitus (Supported by R01 DC003258 to JAK).
The neural code of auditory phantom perception. J Neurosci. 2007 Feb 7;27(6):1479-1484. Weisz N, Muller S, Schlee W, Dohrmann K, Hartmann T, Elbert T Department of Psychology, University of Konstanz, D-78464 Konstanz, Germany. firstname.lastname@example.org
Tinnitus is defined by an auditory perception in the absence of an external source of sound. This conditi- on provides the distinctive possibility of extracting neural coding of perceptual representation. Previously, we had established that tinnitus is characterized by enhanced magnetic slow-wave activity (approxima- tely 4 Hz) in perisylvian or putatively auditory regions. Because of works linking high-frequency oscil- lations to conscious sensory perception and positive symptoms in a variety of disorders, we examined gamma band activity during brief periods of marked enhancement of slow-wave activity. These periods were extracted from 5 min of resting spontaneous magnetoencephalography activity in 26 tinnitus and 21 control subjects. Results revealed the following, particularly within a frequency range of 50-60 Hz: (1) Both groups showed significant increases in gamma band activity after onset of slow waves. (2) Gamma is more prominent in tinnitus subjects than in controls. (3) Activity at approximately 55 Hz determines the laterality of the tinnitus perception. Based on present and previous results, we have concluded that cochlear damage, or similar types of deafferentation from peripheral input, triggers reorganization in the central auditory system. This produces permanent alterations in the ongoing oscillatory dynamics at the higher layers of the auditory hierarchical stream. The change results in enhanced slow-wave activity reflecting altered corticothalamic and corticolimbic interplay. Such enhancement facilitates and sustains gamma activity as a neural code of phantom perception, in this case auditory.
Piezoelectricity increases outer hair cell high frequency response. (Abstract of ARO Meeting Denver, Colorado) Ning Yu, Hong-Bo Zhao University of Kentucky Medical Center
Outer hair cell (OHC) electromotility is a cochlear amplifier and can actively boost the basilar membrane vibration to enhance auditory sensitivity and frequency selectivity. OHC electromotility is membrane-po- tential dependent and driven by cross-membrane voltage. Although the conformation of prestin motor proteins can be rapidly changed up to 100 kHz, its driving force (cross-membrane voltage) would be dramatically attenuated at high frequency by membrane capacitance, which forms a low-pass filter with cut-frequency less than 1 kHz. Outer hair cells also have remarkable piezoelectricity. Mechanically elongating and compressing OHC can produce electric currents. Here, we report that
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