School of Science and Technology, University of New England, Armidale 2351, NSW, Australia.
Brain-Behaviour Research Group, University of New England, Armidale 2351, NSW, Australia.
Rev Neurosci. 2018 Aug 28;29(6):629-643. doi: 10.1515/revneuro-2017-0072.
Gut microbiome diversity has been strongly associated with mood-relating behaviours, including major depressive disorder (MDD). This association stems from the recently characterised bi-directional communication system between the gut and the brain, mediated by neuroimmune, neuroendocrine and sensory neural pathways. While the link between gut microbiome and depression is well supported by research, a major question needing to be addressed is the causality in the connection between the two, which will support the understanding of the role that the gut microbiota play in depression. In this article, we address this question by examining a theoretical 'chronology', reviewing the evidence supporting two possible sequences of events. First, we discuss that alterations in the gut microbiota populations of specific species might contribute to depression, and secondly, that depressive states might induce modification of specific gut microbiota species and eventually contribute to more severe depression. The feasibility of both sequences is supported by pre-clinical trials. For instance, research in rodents has shown an onset of depressive behaviour following faecal transplantations from patients with MDD. On the other hand, mental induction of stress and depressive behaviour in rodents resulted in reduced gut microbiota richness and diversity. Synthesis of these chronology dynamics raises important research directions to further understand the role that gut microbiota play in mood-relating behaviours, which holds substantial potential clinical outcomes for persons who experience MDD or related depressive disorders.
肠道微生物多样性与情绪相关行为（包括重度抑郁症（MDD））密切相关。这种关联源于肠道和大脑之间最近被描述的双向通讯系统，由神经免疫、神经内分泌和感觉神经途径介导。虽然肠道微生物组与抑郁症之间的联系得到了研究的充分支持，但需要解决的一个主要问题是两者之间联系的因果关系，这将有助于理解肠道微生物在抑郁症中的作用。在本文中，我们通过检查一个理论“时间顺序”来解决这个问题，回顾支持两种可能事件顺序的证据。首先，我们讨论特定物种的肠道微生物种群的改变可能导致抑郁症，其次，抑郁状态可能诱导特定肠道微生物物种的改变，并最终导致更严重的抑郁症。这两个序列的可行性都得到了临床前试验的支持。例如，对啮齿动物的研究表明，接受 MDD 患者粪便移植后，会出现抑郁行为。另一方面，在啮齿动物中进行精神诱导应激和抑郁行为会导致肠道微生物丰富度和多样性降低。对这些时间动态的综合分析提出了重要的研究方向，以进一步了解肠道微生物在情绪相关行为中的作用，这对经历 MDD 或相关抑郁障碍的人具有重要的临床应用潜力。
