Circadian regulation of maternal and feeding behaviors in lactating mice.

Maternal care is essential for offspring survival. Circadian regulation of maternal behavior and feeding behavior was determined in mice after parturition. The maternal crouching behavior (covering over pups) occurred intensively in the late half of the dark phase (nighttime), referred to as the "crouching-dominant time." Interestingly, a rapid decrease in body temperature preceded the onset of crouching-dominant time. Feeding behavior during lactation increased in line with the increased energy demand. However, during the night, feeding behavior intensively occurred in the first half of the nighttime, as seen during the non-lactation period, and intermittent feeding behavior was added during the daytime. The clock genes expression of the suprachiasmatic nucleus (SCN) showed robust oscillation even during lactation. In contrast, marked changes in expression profiles of peroxisome proliferator-activated receptor α (PPARα)-regulated metabolic genes in the liver during lactation (postpartum 7 to 12 days) were dissociated from the peripheral clock control, compared to those in virgin mice. During lactation, a critical time for the survival of the species, the maternal circadian clock may regulate multiple important behaviors so that they can occur in the appropriate time frame while adapting to energy requirements.