Neuropeptide signals from the side hypothalamus change daily rhythms in mice

Orexin and MCH peptides influence circadian rhythms in the suprachiasmatic nucleus (SCN) of both sexes.

• Ablation of orexin and MCH neurons results in lengthened circadian behavioral rhythms under constant darkness.
• Orexin and MCH neurons project to the SCN, indicating a direct connection between these neurons and the circadian clock.
• Application of orexin and MCH peptides to cultured SCN slices shortens circadian rhythms and lowers intracellular cAMP levels.
• Pharmacological reduction of intracellular cAMP levels also leads to a shortened circadian period in SCN slices.
• These findings suggest that orexin and MCH peptides may modulate the circadian period in the SCN.

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