https://doi.org/10.36866/pn.113.13

Chronobiology is at the forefront of many researchers’ minds. The Physiological Society’s 2018 theme is “Physiology of our Body Clocks”, there is a Society Meeting called “Sleep and Circadian Rhythms: From Mechanisms to Function”, and the 2017 Nobel Prize for Physiology or Medicine was awarded for work elucidating the genetic makeup of the circadian clock.

Following suit with this themed issue, we asked our journals’ Editors-in-Chief to weigh in on the impact of chronobiology on physiological research from the perspectives of experimental design and journal policy. We would like to thank Kim Barrett (The Journal of Physiology), Mike Tipton (Experimental Physiology), and Thomas Kleyman (Physiological Reports) for their time and informative answers.

Should journals make providing time-of-day information for all experimental interventions and measurements compulsory? Similarly, do you think light intensities and timing of exposure of animals (to handling for health checks, cage cleaning, adding food etc.) should be reported?

KB: There is increasing evidence that a wide range of physiological processes are influenced by factors such as time of day, as well as light exposure during normally dark periods or feeding periods. We have not yet attained sufficient understanding of the impact of chronobiology on all physiological mechanisms studied by our authors to mandate time-of-day reporting for all studies. However, it would not be unreasonable to encourage such reporting, where relevant.

MT: This is already standard practice in some areas (e.g. human physiology) where you will see statements like “the experiments were conducted at the same time of day to avoid circadian variation.” I would leave this consideration to editors and reviewers at present. They should be considering this along with all other possible sources of pre-exposure variation (familiarisation, diet, fluid intake, exercise etc.).

TK: I agree with Mike’s and Kim’s responses. I would not require that authors address issues related to chronobiology. I think it is reasonable to suggest that authors provide a limited amount of information regarding chronobiology in the methods section, including the timing of the day/night cycle and the timing of studies (day vs. night), where applicable.

Do you think that policy concerning aligning the activity periods of nocturnal animals with times when they are more likely to be visited and handled by animal facility staff and researchers, should be implemented? (Staff and researchers would need night-vision goggles).

KB: This is a tricky one. Experimental outcomes in some studies may be influenced by artefacts introduced when normally nocturnal animals are disturbed during their rest periods. However, there are also health and safety issues to be considered for the staff and researchers, to say nothing of the fact that the animals might be subjected to greater stress and even the potential for injury when they are handled or maintained in the dark (even with the benefit of night vision goggles)! Based on my understanding of the latter, I don’t think the technology is currently adequate to allow for appropriate and safe use, particularly when surgical manipulations are planned. The bottom line is that more research is definitely needed.

MT: More studies need to determine the criticality of this aspect. Unanswered questions concern not only laboratory housing but also the choice of animal models and isolation from other factors present in the natural environment e.g. moonlight (Kronfeld-Schor et al., 2013). This question also applies to human studies. For example, should elite athletes preparing to perform in another country (e.g. Tokyo 2020) train at the time of their event in UK time or Japanese time? What about if they go to Japan early enough to adjust their circadian rhythm? There are also limited data to suggest that the timing of acclimatisation is important (Shido et al., 1999) – threshold reductions for the onset of sweating were mostly observed if thermal loading was applied at the same time of day as the original adaptation impulse (“adaptation memory”). Finally, all of our data on humans tend to be collected between 9 am and 5 pm on Monday to Friday. How valuable are these data (e.g. survival time estimations) when a ferry sinks outside of this period?

TK: My impression is that carefully addressing questions related to chronobiology in mammalian systems requires that staff (investigators, postdocs, predocs, techs) be flexible regarding work hours, and be willing to work nights. This is a lot to ask of trainees and technicians, including animal care technicians. Reminds me of when I was training in medicine, and frequently on
night call.

References

Kronfeld-Schor N, Bloch G, Schwartz WJ (2013). Animal clocks: when science meets nature. Proceedings of the Royal Society B: Biological Sciences 280, 20131354.

Shido O, Sugimoto N, Tanabe M, Sakurada S (1999). Core temperature and sweating onset in humans acclimated to heat given at a fixed daily time. American Journal of Physiology 276, R1095-101.