School of Environmental Sciences, University of Liverpool, Liverpool L69 3GP, UK.
Department of Electrical Engineering and Electronics, University of Liverpool, Liverpool L69 3GJ, UK.
J Exp Biol. 2020 Jul 22;223(Pt 14):jeb224527. doi: 10.1242/jeb.224527.
The state of an animal prior to the application of a noxious stimulus can have a profound effect on their nociceptive threshold and subsequent behaviour. In mammals, the presence of acute stress preceding a painful event can have an analgesic effect whereas the presence of chronic stress can result in hyperalgesia. While considerable research has been conducted on the ability of stress to modulate mammalian responses to pain, relatively little is known about fish. This is of particular concern given that zebrafish () are an extensively used model organism subject to a wide array of invasive procedures where the level of stress prior to experimentation could pose a major confounding factor. This study, therefore, investigated the impact of both acute and chronic stress on the behaviour of zebrafish subjected to a potentially painful laboratory procedure, the fin clip. In stress-free individuals, those subjected to the fin clip spent more time in the bottom of the tank, had reduced swimming speeds and less complex swimming trajectories; however, these behavioural changes were absent in fin-clipped fish that were first subject to either chronic or acute stress, suggesting the possibility of stress-induced analgesia (SIA). To test this, the opioid antagonist naloxone was administered to fish prior to the application of both the stress and fin-clip procedure. After naloxone, acutely stressed fin-clipped zebrafish exhibited the same behaviours as stress-free fin-clipped fish. This indicates the presence of SIA and the importance of opioid signalling in this mechanism. As stress reduced nociceptive responses in zebrafish, this demonstrates the potential for an endogenous analgesic system akin to the mammalian system. Future studies should delineate the neurobiological basis of stress-induced analgesia in fish.
动物在受到有害刺激之前的状态会对其痛觉阈值和随后的行为产生深远影响。在哺乳动物中，疼痛事件前存在急性应激会产生镇痛作用，而慢性应激则会导致痛觉过敏。尽管已经对应激调节哺乳动物对疼痛反应的能力进行了大量研究，但对鱼类知之甚少。鉴于斑马鱼（）是一种广泛使用的模式生物，它们会经历各种侵入性程序，而实验前的应激水平可能是一个主要的混杂因素，这一点尤其令人关注。因此，本研究调查了急性和慢性应激对斑马鱼进行潜在疼痛实验室程序（鳍夹）时行为的影响。在无应激个体中，那些接受鳍夹的个体在水箱底部停留的时间更长，游动速度降低，游动轨迹更简单；然而，在首先经历慢性或急性应激的鳍夹鱼中，这些行为变化不存在，这表明可能存在应激诱导的镇痛（SIA）。为了验证这一点，在施加应激和鳍夹程序之前，向鱼施用阿片拮抗剂纳洛酮。在纳洛酮之后，急性应激的鳍夹斑马鱼表现出与无应激鳍夹鱼相同的行为。这表明存在 SIA 和阿片信号在这种机制中的重要性。由于应激降低了斑马鱼的痛觉反应，这表明存在类似于哺乳动物系统的内源性镇痛系统的可能性。未来的研究应该阐明鱼类应激诱导镇痛的神经生物学基础。
