| Summary: | 碩士 === 國立成功大學 === 生理學研究所 === 92 === The inferior colliculus (IC) is a major auditory midbrain structure that is critical for speech-related information processing, sound localization and head reflex to sound. Increasing evidence indicates that IC neurons are very plastic to sound manipulation. For instance, previous electrophysiological studies have shown that in adult IC more neurons are found near the frequency of a priming tone (4 kHz, 65 dB SPL) presented to the animal during the neonatal period and their minimum thresholds are elevated. Currently the GABA-mediated inhibitory neural mechanism has been implicated in sharpening the response properties of IC neurons, which may be reflected in localized changes in properties of the GABAA receptor such as its sensitivity to GABA and its modulation by neurosteriods. Using the whole-cell voltage-clamp technique and pharmacological method, the major goal of this study is thus to determine the effect of prolonged pure tone exposure (4 kHz, 65 dB SPL for 7 days form postnatal day 7 to 14) on the GABA concentration-response curve and the activity of neurosteriods such as pregnenolone sulfate (PS) and 5α-pregnan-3α-ol-20-one (5α3α to modulate the GABA-induced current in acutely dissociated rat IC neurons. Results revealed that sound treatment decreased the GABA EC10-EC30 and the Hill coefficient with little effect on the GABA maximal response and EC50, indicating the enhancing effect of sound exposure on the response induced by lower concentrations of GABA. In addition, prolonged pure tone exposure had no effect on the inhibition by PS of the GABA-induced current. However, the same sound treatment dramatically enhanced the activity of 5α3α to positively modulate the GABAA receptor. Taken together, our results support the idea that the properties of GABAA receptors in IC neurons are subject to plastic changes by prolonged pure tone exposure, which may cause the IC neurons to elevate their minimum thresholds and to become habituated after repeated sound exposure.
|
|---|
