乙醯膽鹼如何調控螯蝦的尾端感光細胞?

在螯蝦(Procambarus clarkii)的神經網路裡，有些特定刺激會產生特定行為，並不需要經過大腦思考。若兩種刺激引發的行為不能同時執行，螯蝦最後只會出現一種行為，神經網路要如何協調呢？在這篇論文裡面，我們利用螯蝦對於光線和碰觸兩種刺激，引發兩種不能同時執行的行為反應，來討論協調機制。螯蝦突然暴露在明亮的環境，會步行後退(backward walking)，但是尾扇被碰觸則會引起步行前進。根據我們的觀察，光線和碰觸這兩種刺激同時給予，通常導致螯蝦前進，這和純粹碰觸尾扇造成的行為相同。將螯蝦去除視覺之後，螯蝦仍然擁有避光行為，其感光能力是來自尾端的一對感光細胞(caudal photoreceptor)，簡稱CPR。它的感光部分位在腹部最後一個神經節，當黑暗中突然受到光線刺激時，CPR會產生高頻神經衝動，最後造成螯蝦產生後退行為，這一連串動作通常是蜷曲腹部收起尾節，並一路倒退步行到陰影內。而CPR也會接受機械感受神經元(mechanoreceptor neuron，簡稱MRN) 調控，MRN是螯蝦用來感受水流及碰觸的偵測器。利用電生理技術量測CPR的神經衝動頻率，我們的實驗結果支持，尾扇周圍水流的刺激經由MRN，可以壓抑光所誘發的CPR高頻神經衝動，可能進而阻止CPR誘發的後退行為。更進一步研究，支持MRN透過乙醯膽鹼調控CPR的神經衝動頻率；活化尼古丁類(nicotinic)和毒蕈膽鹼類(muscarinic)兩種乙醯膽鹼受器，都可以壓抑光誘發CPR所產生高頻神經衝動。

關鍵字

螯蝦；尾端感光細胞；乙醯膽鹼

並列摘要

For crayfish (Procambarus clarkii), the brain is not necessary for some specific behaviors elicited by certain external stimuli. How do the neural network coordinate and/or integrate with two stimuli which evoke incompatible behaviors? In this study, we will investigate the possible regulatory mechanism by examining the incompatible behaviors elicited by light and touch . Crayfish walks backward when abruptly exposed to light but moves forward when its tail fan is stimulated by mechanical stimulation. Based on our observation, if light and touch were given simultaneously, crayfishes usually moved forward, which is in line with the behavior caused by simply touching the tail fan. Crayfish still have photonegative behavior while deprived of vision. Its photosensitivity comes from a pair of caudal photoreceptors (CPR). The light sensor of CPR is at the last abdominal ganglion. CPR will produce high-frequency impulses when suddenly exposed to light in the dark and then lead the crayfish to walk backward to the shadow. The backward walking is usually accompanied by the abdominal and tail flexion. CPR will also be regulated by mechanoreceptor neuron (MRN), which senses mechanical stimulation such as water flow and touch. We measure the spike rates by the electrophysiological technique. Our results supported that the mechanical stimulation on the tail fan can inhibit the high-frequency impulses evoked by CPR via MRN. It implies that mechanical stimulation on the tail suppresses the CPR-induced backward walking by MRN inhibiting CPR. Another research suggested that MRN could regulate the spike rates of CPR by acetylcholine. Activating nicotinic and muscarinic acetylcholine receptors could also depress the light-evoked high frequency impulses of CPR.

並列關鍵字

crayfish ； caudal photoreceptor ； CPR ； acetylcholine ； nicotinic ； muscarinic

參考文獻

Beall, S.P., Langley, D.J., and Edwards, D.H. (1990). Inhibition of escape tailflip in crayfish during backward walking and the defense posture. J Exp Biol 152, 577-582.

Bristol, A.S., and Carew, T.J. (2005). Differential role of inhibition in habituation of two independent afferent pathways to a common motor output. Learn Mem 12, 52-60.

Calabrese, R. (1976b). Crayfish mechanoreceptive interneurons. II. Bilateral interactions and inhibition. J comp Physiol 105, 103-114.

Cattaert, D., Araque, A., Buno, W., and Clarac, F. (1994). Nicotinic and muscarinic activation of motoneurons in the crayfish locomotor network. J Neurophysiol 72, 1622-1633.

Cattaert, D., Pearlstein, E., and Clarac, F. (1995). Cholinergic control of the walking network in the crayfish Procambarus clarkii. J Physiol Paris 89, 209-220.

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乙醯膽鹼如何調控螯蝦的尾端感光細胞?

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