Effects of Fasting-Induced Torpor in Mice

全世界许多实验室在行为神经科学、代谢和昼夜神经生物学研究的背景下常规使用小鼠的食物限制、禁食或定时喂养。饥饿与血糖降低有关，血糖降低会引发失眠和觅食行为。许多物种在面临食物短缺时采用的另一种策略是节能，这可以通过进入休眠来实现。麻痹是一种独特的适应，其特征是生理功能的严重衰减，其中体温可以下降到环境温度的几度之内。有人提出，禁食阻断冷诱导的产热，同时引发能量消耗和体温下降，导致麻木。令人惊讶的是，很少有研究人员意识到，实验室小鼠是一种兼性异温物种，在动物设施常用的温度水平下，当食物匮乏时，它们很容易表现出麻木。虽然昏睡本身是对有限食物供应的适应性反应，并且很容易逆转，但人们对昏睡对生理，睡眠和大脑功能的持久影响知之甚少，因此它可能是科学数据中重要生物变异的潜在来源。研究表明，麻木和体温过低会导致整个大脑的突触大量丢失，包括海马体，皮层和丘脑，这表明它可能会对行为和学习产生根本性的影响。有证据表明，睡眠迟钝与代谢率的深刻变化和瘦素等激素的变化有关。因此，由于大多数研究人员不知道禁食小鼠可能会经历长时间的麻木，因此有必要在常用的食物限制范式的背景下研究这一过程，以确定麻木对后续数据的影响。本项目将研究常用的食物限制方案对小鼠麻木的影响，麻木对后续行为表现和睡眠的影响，并会制订一套标准化的方法，以侦测食物限制期间出现的昏睡情况。我们的项目将为广泛使用食物限制的小鼠的行为和生理研究提供信息。我们的初步研究表明，即使是短时间的食物限制也会导致麻木，这与对睡眠和清醒的深刻影响有关。鉴于睡眠对认知功能和能量稳态至关重要，因此，麻痹的发生将对动物随后的行为任务表现和许多生理变量产生显著影响。因此，我们的项目将为未来研究的实验设计提供信息，以确保禁食足够而不会诱导麻木。这将提供一个主要的3R影响，因为它将允许食物限制协议得到优化，同时避免与麻木相关的主要代谢紊乱，这有可能破坏行为和学习（细化）。此外，我们预测这也将减少数据的方差，减少此类研究所需的动物数量（减少）。科学性，以及提高可重复性和避免混淆，这个模型提供了一个独特的机会，了解麻木作为第三个基本的警觉状态，除了清醒和睡眠。

Food restriction, fasting or scheduled feeding in mice are routinely used in many laboratories worldwide in the context of behavioural neuroscience, studies on metabolism and circadian neurobiology. Hunger is associated with a reduction in blood glucose, which triggers wakefulness and food-seeking behaviour. An alternative strategy that many species employ when facing food scarcity is energy conservation, which can be achieved by entering torpor. Torpor is a unique adaptation, characterised by a profound attenuation of physiological functions, wherein body temperature can drop to within a few degrees of ambient temperature. It has been proposed that fasting blocks cold-induced thermogenesis while triggering a decrease in energy expenditure and body temperature, resulting in torpor. Surprisingly few researchers are aware that laboratory mice are a facultative heterothermic species that readily display torpor bouts in response to food deprivation at the temperature levels commonly used in animal facilities. While torpor itself is an adaptive response to limited food supply, and is easily reversible, little is known about the lasting consequences of torpor on physiology, sleep and brain function, and thus it may be a potential source of significant biological variation inscientific data. Studies suggest that torpor and hypothermia lead to a substantial loss of synapses across the brain including the hippocampus, cortex, and thalamus, suggesting that it will likely have fundamental influences on behaviour and learning. Evidence also suggests that torpor is associated with profound changes in metabolic rates and changes in hormones such as leptin. Therefore, since most researchers are unaware that fasted mice may undergo prolonged periods of torpor, it is essential to investigate this process in the context of commonly used food restriction paradigms to determine the influence of torpor on subsequent data.This project will investigate the effects of commonly used food restriction protocols on torpor in mice, the effects of torpor on subsequent behavioural performance and sleep, and will develop a standardized approach to detect the occurrence of torpor during food restriction. Our project will inform behavioural and physiological studies in mice, where food restriction is widely used. Our preliminary study suggests that even a short period of food restriction can induce torpor, which is associated with profound effects on sleep and waking. Given that sleep is crucially important for cognitive functions and energy homeostasis, the occurrence of torpor will therefore have a marked influence on animal's subsequent performance in behavioural tasks and on many physiological variables. Our project will therefore inform the experimental design of future studies to ensure that fasting is sufficient without inducing torpor. This will provide a major 3Rs impact, as it will allow foodrestriction protocols to be optimised whilst avoiding the major metabolic disturbances associated with torpor, which have the potential to disrupt behaviour and learning (Refinement). Moreover, we predict that this will also decrease variance in the data reducing the number of animals required for such studies (Reduction). Scientifically, as well as improving reproducibility and avoiding confounds, this model offers a unique opportunity to understand torpor as a third fundamental state of vigilance, in addition to wake and sleep.