催產素神經於斑馬魚低溫適應之角色

Abstract

面對環境溫度波動，外溫動物的行為與代謝的生理調整是抵禦外界壓力的主要方法；水體溫度降低促使魚類增加離子調節機制以維持細胞運作，而催產素具有協助滲透壓調節的功能，推測催產素參與低溫適應中的生理調節。而催產素受中樞神經系統中的催產素神經元所分泌，該神經元具有釋放分子進入血液循環與調控其他神經活化的功能，影響器官生理以及社交、攝食等行為。催產素在魚類低溫適應下除了生理調節功能外，催產素神經元的活性與行為上的影響尚未明瞭，本研究主要探討斑馬魚低溫適應下催產素神經元活性變化及其迴路與打鬥與攝食行為調控關係與代謝反應。 低溫處理下，斑馬魚體內催產素在短時間釋放增加，長期適應以增生腦中催產素神經細胞，增加催產素功能。在受24小時處理後斑馬魚有較高的機會成為輸的一方以及打鬥行為表現的減少。催產素神經纖維投射至與打鬥與攝食行為相關核區：背側腳間窩（dorsal interpeduncular nucleus, dIPN）、背縫核區（median raphe nucleus, MR）以及後端中央灰層（griseum centrale, GC）。然而催產素神經細胞活化情形並未受到低溫影響。另外在攝食減少上推測是背縫核反應相關，但代謝的降低並沒有明顯趨勢。本研究提出了低溫適應下催產素神經迴路對於攝食行為調控的可能路徑，以及低溫生理代謝對於其行為表現之影響，然而催產素與打鬥行為的關聯性有待更多證據支持。

Behavioral changes and physiology modifications are the most important way to adapt temperature fluctuations such as enhanced ionic regulation under cold stress in fish. Isotocin, which is produced by isotocin neurons in the central nervous system, have been demonstrated to play a role in osmoregulation in fish. Isotocin can affect behavior such as regulate feeding and social responses through the nervous system. It can also be released as a neurohormone to modulate targeted organs. However, because the understanding of the role of isotocin in fish during cold acclimation is mainly focused on physiological adjustment, the influence of isotocin neuron on nervous system and the change of behavior regulated by isotocin neuron under cold stress in fish are unclear. The number of isotocin neuron in the brain increased under 7 days cold treatment. The 24 hours cold treated fish had a tendency to lose in the dyadic fighting test, the fighting rate also decrease in cold water. Isotocin neural projections to many nuclei in a neural circuit related to fighting and feeding behavior, including the dIPN (dorsal interpeduncular nucleus), MR (median raphe) and the GC (griseum centrale). However, the activation of isotocin neurons is same in normal and cold water in zebrafish. The foraging behavior was significantly suppressed after cold treatment, the activation of the MR supposed to regulate this suppression. In addition, we also observe physiological adjustment. There is a tendency to increase plasma isotocin concentration under 3 hours cold treatment. The oxygen consumption did not change upon cold treatment. However, the protein metabolism decreased for short term cold acclimation. Overall, this study suggests that the neural activity of isotocin increase during cold acclimation and the isotocin-related neural pathways may regulate foraging behavior. We will further investigate the relationship between isotocin neural circuit and behavior.