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Resetting the Circadian Clock
Fatigue and other symptoms of jet lag arise when the body's internal circadian clock is out of sync with environmental light-dark cycles. Studying genetically modified mice lacking two receptors for the peptide hormone vasopressin under experimental conditions simulating jet lag, Yamaguchi et al. (p. 85; see the Perspective by Hastings) concluded that vasopressin signaling in the suprachiasmatic nucleus (SCN)—a region of the brain known to control circadian rhythms—impedes adjustment to the environmental clock. Infusion of vasopressin receptor antagonists directly into the SCN of wild-type mice accelerated their recovery from jet lag, suggesting that this pathway may merit further investigation as a pharmacological target for treating jet lag.
Jet-lag symptoms arise from temporal misalignment between the internal circadian clock and external solar time. We found that circadian rhythms of behavior (locomotor activity), clock gene expression, and body temperature immediately reentrained to phase-shifted light-dark cycles in mice lacking vasopressin receptors V1a and V1b (V1a–/–V1b–/–). Nevertheless, the behavior of V1a–/–V1b–/– mice was still coupled to the internal clock, which oscillated normally under standard conditions. Experiments with suprachiasmatic nucleus (SCN) slices in culture suggested that interneuronal communication mediated by V1a and V1b confers on the SCN an intrinsic resistance to external perturbation. Pharmacological blockade of V1a and V1b in the SCN of wild-type mice resulted in accelerated recovery from jet lag, which highlights the potential of vasopressin signaling as a therapeutic target for management of circadian rhythm misalignment, such as jet lag and shift work.