Most adults produce less urine at night than during the day, and store more of what is made, thanks to the circadian regulation of daily urination patterns.

Hitoshi Okamura and Osamu Ogawa at Kyoto University in Japan and their colleagues developed a machine that measures the urine discharges of mice, as stains on paper (pictured), over time. They focused on a protein, connexin43, which increases the frequency of urination by making the bladder muscles more sensitive to neural signals. They found that connexin43 levels peaked during the night when the nocturnal creatures were active. Mice without the circadian clock gene Cry produced less connexin43 during the night than did normal mice, and did not show daily rhythms in urination patterns. Another clock gene, Rev-erbα, regulates connexin43 expression.

The authors suggest that other genes related to bladder-muscle contraction and daily cycles might also have a role in staving off night-time trips to the toilet.

Nature Commun. http://dx.doi.org/10.1038/ncomms1812 (2012)