多巴胺參與調控德國蜚蠊活動行為

Abstract

日周律動是一個周期大約為24小時且存在於大部分的生物體中的生物時鐘。在德國蟑螂雌成蟲的性接受期中，具有日周律動的活動行為被找尋配偶的活動行為所遮蓋並且呈現整天均勻分布，然而德國蟑螂雄成蟲找尋交配的活動行為仍然局限於夜間。由於多巴胺(dopamine)是一種神經傳導物質，參與從腦到肌肉的訊息傳導，最後影響到活動行為，故我們推測多巴胺可能是日周律動活動行為的遮蓋因子。此外，多巴胺在昆蟲內扮演非常重要的角色，它參與學習、取食、活動行為及生殖的調控。酪胺酸羥化酶(tyrosine hydroxylase)及多巴脫羧酶(dopa decarboxylase)是生物體內合成多巴胺的必要酵素，並且在雄成蟲及雌成蟲中，它們的mRNA表現量與活動行為的模式相符合。在雄成蟲的頭中，酪胺酸羥化酶及多巴脫羧酶的mRNA表現量均表現日周律動，在雌成蟲的頭中，則沒有呈現日周律動。另外，酪胺酸羥化酶及多巴脫羧酶的mRNA表現量在性接受及非性接受期雌蟲的卵巢並無顯著差異，且多巴胺接受器1及2的mRNA在非性接受期雌蟲的卵巢沒有偵測到。在注射多巴胺及多巴胺拮抗劑至雄成蟲和雌成蟲體內後，活化劑造成總活動量的上升，拮抗劑造成總活動量的下降，但此效果只能維持一天。除此之外，注射活化劑及拮抗劑後儘管可以改變總活動量，卻不改變活動量的日周律動表現。這些結果顯示多巴胺確實參與較下游活動行為的調控，但不影響生物時鐘的表現。

Circadian clock is a 24-hour internal clock existing in almost every organism on Earth. The locomotor circadian rhythm of virgin female adults of the German cockroach is masked by increasing mate-finding activity and even-distributed throughout the day during sexually receptive period, even though male adults still cofine their mate-finding activity at night. Since dopamine (DA) is a neurotransmitter involving in signal transduction from brain to muscle, it serves as a potential masking factor on locomotor circadian rhythm. Furthermore, it plays multiple roles in the regulation of learning, feeding, locomotion and reproduction in insects. In the synthesized cascade of dopamine, tyrosine hydroxylase and dopa decarboxylase are the essential enzymes, and circadian rhythmicity of their mRNA expression levels are consistent with locomotor activity patterns of male and female adults. The mRNA expression level of tyrosine hydroxylase and dopa decarboxylase in male adults displayed circadian rhythm, but none of them displayed circadian rhythm in virgin female adults. Moreover, tyrosine hydroxylase and dopa decarboxylase mRNA expression levels had no significant difference between sexually and non-sexually receptive female adults’ ovary and dopamine receptor 1 and receptor 2 mRNA were not detected in the non-sexually receptive female adults’ ovary. The effect of extra dopamine and antagonist (cis(Z)-flupenthixol) on locomotor activities of male and female adults only last for one day. In addition, extra dopamine and antagonist injection did not alter the expression of circadian rhythm in both male and female adults regardless the changes in total locomotor activities. These results suggest that dopamine does participate in downstream regulation of locomotion without affecting the circadian clock.