Influence of Monaural Plugging on Postnatal Development of Auditory Spatial Sensitivity of Inferior Collicular Neurons of the Big Brown Bat, Eptesicus fuscus

單耳阻塞對大灰褐色蝙蝠出生後下丘神經元聽方向靈敏性形成的影響

任晃蓀(Philip H. S. Jen) ； 孫心德(Xin-De Sun)

《The Chinese Journal of Physiology》 33卷3期 (1990/09) Pp. 231-246

摘要

本實驗係探討單耳阻塞對大灰褐色蝙蝠出生後聽覺神經元方向靈敏性形成的影響。實驗分别在出生後58-69天的對照組及實驗組小蝙蝠下丘視神經元進行。實驗組小蝙蝠依次出生後7,14, 及35天以棉花及牙膠進行單耳阻塞。每一下丘聽神經元方向靈敏性的測定係以測量該神經元對一最佳頻率的聲源以等距離循序置於不同水平方位時該神經元動作電位的發放數目及其最低閾值的變化程度來決定。實驗结果顯示單耳阻塞雖不影響兩組小蝙蝠下丘聽神經元的動作電位發放樣式以及最佳頻率與反應潛伏期的分佈範圍，但郤提高了實驗組小蝙蝠下丘神經元的最低閾值約21-24分貝，並改變其方向靈敏性。因此實驗小蝙蝠下丘聽神經元的方向靈敏性在耳塞移去較移去前後靈敏。尤有進者，下丘神經元之方向靈敏性以及神經元反應中心在聽空間的分佈在耳塞移去前的測量结果與控制組的測量結果極為類似。此結果顯示形成實驗組小蝙蝠聽神經元方向靈敏性的神經網路在出生後經過重整以適應因單耳阻塞而造成的不自然雙耳聲刺激偏差。本實驗亦對出生後49及60天的控制組小蝙蝠及一支大於一歲的成年蝙蝠的聽方向靈敏性進行測量。測量結果顯示，下丘聽神經元的方向靈敏性在出生後一直不斷地加强，此加强的過程至少在出生後60天尚在持續。

並列摘要

Postnatal development of auditory sensitivity in the big brown bat, Eptesicus fuscus, was studied by determining the auditory spatial sensitivity of inferior collicular (IC) neurons of juvenile bats which were raised under normal (control) or monaurally plugged conditions. The auditory spatial sensitivity of each IC neuron was determined by measuring its variation in number of impulses and minimum threshold to a best frequency sound delivered from different azimuthal angles under free field stimulation conditions. Monaural plugging was performed on different juvenile bats at 7, 14, and 35 days of age. Auditory spatial sensitivity was then determined for IC neurons of monaurally plugged bats at 58-69 days after birth. Monaural plugging did not alter the discharge pattern, distribution of best frequency and latency of IC neurons, but it raised the minimum threshold of IC neurons of plugged juvenile bats by an average of 21-24 dB. Monaural plugging also appeared to modify postnatal development of auditory spatial sensitivity. The auditory spatial sensitivity of IC neurons was sharper when the earplug was intact than when the earplug was removed. Thus, the distribution of response center and the spatial sensitivity of IC neurons of the monaurally plugged bats was more comparable to IC neurons of the control bats before the earplug was removed. These findings suggest that the neural circuits underlying auditory spatial sensitivity of IC neurons of the monaurally plugged juvenile bats have undergone modifications to compensate for the unnatural binaural disparity during postnatal development. The auditory spatial sensitivity was also determined for two control juvenile bats at 49 and 60 days of age and for an adult bat (more than 1 year). Our data show that auditory spatial sensitivity of IC neurons sharpens with postnatal age. Furthermore, the sharpening process appears to be still in progress even at 60 days after birth.

並列關鍵字

inferior colliculus ； auditory spatial sensitivity ； postnatal development ； bats