Impact of anaesthesia on circadian rhythms and implications for laboratory experiments

General anaesthesia is a widely used tool to enable surgery in animal experimentation. There is now convincing evidence that general anaesthesia can cause profound and strongly time-dependant shifts in circadian rhythms of behaviour (sleep-wake cycles), physiology (core body temperature, blood pressure, heart rate and hormone release) and cognitive parameters (learning and memory) in a range of species. These effects have the potential to confound laboratory experiments, and may lead to misinterpretation of results. Here, we summarise these effects and advise caution to those conducting laboratory experiments in which anaesthesia forms part of the protocol.