Remimazolam-induced anesthesia does not affect circadian rhythms significantly in mice

Although inhalational general anesthesia affects mammalian circadian rhythms, which are generated through oscillations in expression of clock genes in the suprachiasmatic nucleus (SCN), the impact of intravenous benzodiazepine (BDZ)-induced general anesthesia is not well understood. We investigated the effects of remimazolam (RMZ), an ultra-short-acting BDZ that has recently gained widespread use in clinical anesthesia, on circadian rhythms and clock gene expression in the SCN in male C57BL/6J mice. Phase shifts in behavioral rest-activity circadian rhythms were quantitatively measured under constant dark conditions. No significant differences were detected among the interventions tested: continuous RMZ injection, bolus RMZ injection, and saline injection at different circadian times. Analyses of day/night activity distribution and the percentage of mice in inactivity bouts showed no significant differences among these groups. To assess the effects of RMZ on clock gene expression, we used continuous RMZ injection, which better reflects clinical anesthesia conditions. Quantitative real-time polymerase chain reaction revealed that the mRNA expression levels of major clock genes Per2, Bmal1, Cry1, and Npas2 in the SCN were decreased, whereas the neuronal activity marker Egr1 was increased. The period of circadian oscillations in clock gene Per2 expression-analyzed by bioluminescence rhythms of cultured SCN tissue from PER2::LUC mice-did not change with any concentration of RMZ administration. Our findings show that RMZ has minimal effects on circadian rhythms under our experimental protocols, suggesting that RMZ has the potential to reduce complications related to circadian rhythm disruption by general anesthesia.