動機，像是口渴和飢餓，對於生存非常重要，在構造簡單的生物裡也是。生物運 用神經系統調控這些行為。但口渴究竟如何驅使神經系統去控制找水行為依舊不 清楚。因此我們利用果蠅(Drosophila melanogaster)去探討此動機行為。 先前文獻指出，多巴胺在果蠅找水行為中扮演重要角色。當我們讓果蠅缺失 dopamine receptor 中的 DAMB 時，發現到會影響找水行為。同樣的，我們在 Kenyon cell 和特定的 mushroom body output neuron (MBON)裡缺失 DAMB 也會影 響找水行為。Mushroom body (MB)在嗅覺的學習和記憶扮演重要的角色，而 Kenyon cell 和 MBON 都是 MB 的一部分。以上我們的實驗顯示，dopamine 在 MB 裡 可能調控找水行為。此外，發現這機制出現在能偵測濕度的感覺神經裡，DAMB 在 感覺神經裡缺失也會影響到找水行為。先前我們實驗室的數據指出，渴的果蠅中 Leucokinin (LK)神經的活性會上升，這代表渴可能調控 LK 的釋放。同時我們發 現在 DAN (Dopaminergic neuron)裡減弱 LK 受器的表現也會影響到找水行為。由 以上的結果，我們推測渴可能調控 LK 的釋放，並且影響到 dopamine 的釋放，進 而影響找水行為。綜合以上實驗結果，我們推測出找水行為的神經迴路。;Primary motivations, such as hunger and thirst, are essential for survival, even in simple animals. How thirst affects the nervous system to control water-seeking behavior is still unknown. We investigate these questions in the fruit flies Drosophila melanogaster. Previous studies have suggested that dopamine is important for thirst-driven water- seeking behavior in the flies, but detail mechanisms remain elusive. Here, we showed that flies lacking dopamine receptor DAMB exhibit impaired water-seeking behavior. Knockdown of DAMB in Kenyon cells (KCs) and mushroom body output neurons (MBONs) caused defective water-seeking behavior in thirsty flies. KCs and MBONs are two major cell types in the mushroom body (MB), a paired neuropil important for olfactory learning and memory. Our data, therefore, suggest that thirst regulates water- seeking behavior via dopamine signals in the MB circuit. Furthermore, we found that RNAi knockdown of DAMB in sensory neurons that detect environmental humidity as well as in the neurons postsynaptic to these sensory neurons also compromised thirsty flies’ water-seeking behavior. These data indicate that thirst might modulate both periphery and central neural circuits to control flies’ response to water vapor. We recently found that the neuronal activity of a pair of leucokinin-releasing neurons in the fly’s brain elevates when a fly is deprived of water. Interestingly, knockdown of leucokinin receptor in dopaminergic neuron (DANs) innervating the MB impaired water-seeking behavior in thirsty flies. We hypothesize that the motivational property of thirst in the fruit flies is mediated by leucokinin and dopamine signals. We found that thirst regulates water- seeking behavior by inhibiting PAM-β′2mp DANs as well as activating PAM-β2β′2a and PAM-β′2a DANs. Taken together, we propose a putative circuit mechanism mediating thirst-control of water-seeking behavior in Drosophila.
