A team of researchers has found that the body’s circadian rhythm increases feelings of thirst a couple of hours before sleep. The findings may help scientists better understand how the biological clock works, potentially leading to treatments for problems resulting from jetlag and graveyard shifts. The details are in a paper that was just published in the journal Nature.
Past research had already shown that mice become thirsty in the hours leading up to sleep. This wasn’t due to dehydration and the mice would drink water even when completely hydrated.
Scientists from the Research Institute of the McGill University Health Centre withheld water from a group of mice during the time before sleep when they would normally become thirsty. The mice became dehydrated by the end of their sleep period, showing that the increased thirst was a safeguard to keep them hydrated throughout the night.
The team wondered which mechanisms were controlling this scheduled thirst response. They used special cells that fluoresce in the presence of vasopressin, a neuropeptide that was suspected to be involved. Vasopressin is released by the suprachiasmatic nuclei, a region of the brain that helps control the circadian clock. As expected, the team noticed a surge in vasopressin release when they artificially stimulated the suprachiasmatic nuclei. Further research, accomplished by turning neurons on and off, confirmed that vasopressin switches thirst neurons “on”. This causes increased thirst in mice and other animals, including humans.
The team’s findings provide new insights into the brain’s circadian clock. In order to keep the body hydrated throughout the entire sleep period, the suprachiasmatic nuclei release vasopressin, stimulating thirst. The study’s authors believe that this new information could help researchers better understand how circadian rhythms work. Third shift workers are forced to go against their natural circadian clock, for example, and they could potentially be treated for problems that arise.
Gizowski et al. Clock-driven vasopressin neurotransmission mediates anticipatory thirst prior to sleep. Nature (2016).