It's all in the Timing! The Effects of General Anaesthesia and Light on the Mouse Circadian Clock

Abstract

Postoperative patients often develop sleep disturbances which can significantly impair their recovery. General anaesthesia (GA) may be a significant contributing factor as there is increasing evidence of GA disrupting the circadian clock, which controls sleep. In honeybees, daytime administration of isoflurane anaesthetic elicits behavioural phase delays under constant conditions (3.5-hours) and in the presence of strong light/dark cycles (1.24 hours). Concurrent exposure to light and anaesthesia effectively eliminated this phase shift. Historical work in hamsters suggested GA blocked the effects of light on the mammalian clock. However, preliminary work from our group indicate the effects of GA and light on the circadian clock is more complex and potentially time-dependent in nature. This thesis aimed to: 1) characterize the time-dependent interaction of GA and light on mammalian behavioural rhythms and 2) to investigate whether GABAA receptors (GABAA-R) mediated the effects of GA on the circadian clock. Phase response curves for 4-hours of light (400 lux, n=58) and 4-hours of isoflurane + light (1.5% in 100% oxygen, n=60) were constructed using an Aschoff type I protocol. Locomotor activity rhythms of adult, male C57BL/6 mice were recorded before and after treatment. Immunohistochemistry and density analysis of α1 and γ2 GABAA-R subunits were conducted on mouse brain tissue collected from isoflurane + light (n=10) and light-only (n=10) treatment groups at distinct circadian times (CT2-4 and CT8-12). Concurrent administration of isoflurane and light was found to induce behavioural phase shifts in a time-dependent manner. The maximum elicited phase delay (-1.05 hours) was comparable to isoflurane-only treatment (-1.11 hours) but significantly smaller than light-only treatment (- 3.34 hours). A weak trend suggested increased γ2 subunit expression in the SCN following treatment with GA exposure. In addition, there was a strong association between α1 subunit expression in the SCN and CTs of sizeable behavioural phase shifts, suggesting a potential role as a marker of circadian phase shifting. These findings demonstrate a time-dependent interaction between GA and light that may be partly mediated by different GABAA-R’s subpopulations. Elucidating the mechanisms underlying the effects of GA on the circadian clock will lead to new ways of combating postoperative sleep disruption.