蚯蚓(纖細遠盲蚓)照射紫外線B後產生激烈運動行為的研究

Abstract

蚯蚓多生活於土壤中，但在大雨過後的清晨，常可看到許多蚯蚓爬出地表，進而陳屍於地表。根據前人的研究發現，紫外線照射會影響蚯蚓的爬行，推測紫外線可能為造成蚯蚓陳屍地表的原因。本實驗以在台灣大雨過後常可見爬出地表的物種纖細遠盲蚓(Amynthas gracilis)作為研究對象，該物種在照射紫外線-B (UV-B)時會產生不正常的S形運動和跳動等行為反應，並且對碰觸刺激變得敏感，因此本實驗目的在探討紫外線-B (UV-B)影響蚯蚓運動模式的機制。首先，在c-Fos做為神經細胞活性指標的實驗中發現，蚯蚓經過紫外線B的照射後，蚯蚓的腹神經索中確實有神經細胞被活化，表示紫外線B確實可以影響蚯蚓神經的活性，於是進一步探討紫外線B如何調控蚯蚓的神經系統以達到影響運動的效果。蚯蚓照射紫外線B會影響蚯蚓的AChE活性，並使神經的PKCα活性上升，而這樣的活性變化皆不是酵素直接吸收紫外線所造成的，AChE是神經突觸間重要的酵素，可分解acetylcholine (ACh)，調控神經傳導物質作用的時間; PKC已知為脊椎動物神經細胞內重要的細胞訊息傳遞物質，可調控鈣離子通道，影響神經傳導物質ACh的釋放，或是調控合成ACh的酵素choline acetyltransferase的活性，達到調控神經傳導的效果。利用PKC活化劑PMA以及鈣離子通道A23187改變PKC的活性，皆可發現會促進蚯蚓照射紫外線B時的運動行為，而鈣離子通道的抑制劑則會抑制蚯蚓照射紫外線B產生的運動，AChE抑制劑chlorpyrifos的處理也會對蚯蚓的運動產生促進效果，由此可知，AChE和PKC活性的改變，確實會影響蚯蚓在紫外線照射下所出現的行為反應，因此推論紫外線會藉由改變這兩個酵素活性來影響蚯蚓的運動模式。

Earthworms usually live in the soil, but some earthworms could be found lying dead on the surface of the ground after a heavy rain. UV radiation was suspected to affect earthworm crawling. Since earthworms, Amynthas gracilis, are often observed lying on the soil surface after a heavy rain in Taiwan, the earthworms were used as an animal model in this experiment. Under UV-B exposure, they showed the abnormal behaviors, the S-shape movement and the jumping behavior. Therefore, the purpose of this experiment is to determine how the UV-B radiation affects the earthworm movement behaviors. Some Fos-labelled cells in earthworm ventral nerve cord were shown after the UV-B radiation. This suggested that some neurons were activated by UV-B radiation. The UV-B radiated nerves were found to have higher protein kinase Cα (PKCα) activity, an effect not mediated by direct UV-B absorption. PKC might regulate the calcium channel(s) to increase the intracellular calcium concentration to alter acetylcholine (ACh) release and choline acetyltransferase to affect ACh synthesis in presynaptic cells. The treatment of PKC activator, PMA and calcium ionophore, A23187 both enhanced the abnormal behavior caused by UV-B radiation. And calcium channels blocker, verapamil blocked the jumping behavior caused by UV-B radiation. On the other hand, the UV-B radiation also affected the activity of acetylcholinesterase (AChE), a key enzyme in the synaptic cleft for ACh hydrolysis. Again, AChE activity was not affected by direct UV-B absorption. And AChE inhibitor, chlorpyrifos, treatment enhanced the earthworm behavior. Together, all of those results support that PKCα and AChE are involved in the regulation of earthworm movement caused by UV-B radiation.