![]() ![]() Remarkably, however, the reduction in RWA starts very early in pregnancy before there is any significant increase in metabolic load, even before implantation ( Ladyman et al., 2018a Slonaker, 1925), and thus, can be considered an anticipatory adaptation in preparation for the future metabolic demands. This profound change in behavior is likely important to offset the prolonged elevation in basal metabolic rate characteristic of pregnancy ( Ladyman et al., 2018a Forsum and Lof, 2007 Morrison, 1956). Using a mouse model to characterize metabolic adaptations in pregnancy, we have shown that along with increases in energy intake, pregnant females rapidly lower their energy expenditure and physical activity levels, as measured by daily voluntary running wheel activity (RWA Ladyman et al., 2018a). ![]() To enable the pregnant female to cope with these demands, hormonal changes associated with pregnancy drive a wide range of adaptations to maternal physiology, and in particular, complex changes in metabolic function ( Napso et al., 2018). The sustained changes in metabolic rate typical of pregnancy have been described as ‘at the limits of human physical capability,’ similar to that expended in extreme physical activity such as an ultramarathon, but over a longer timeframe ( Thurber et al., 2019). Pregnancy and lactation represent profound physiological challenges. Our data demonstrate a key role for prolactin in suppressing voluntary physical activity during early pregnancy, highlighting a novel biological basis for reduced physical activity in pregnancy. As pregnancy progresses, prolactin action continues to contribute to the further suppression of RWA, although it is not the only factor involved. Deletion of Prlr specifically from the medial preoptic area, a brain region associated with multiple homeostatic and behavioral roles including parental behavior, completely abolished the early pregnancy-induced suppression of RWA. We show that prolactin can acutely suppress RWA in non-pregnant female mice, and that conditional deletion of prolactin receptors (Prlr) from either most forebrain neurons or from GABA neurons prevented the early pregnancy-induced suppression of RWA. ![]() Here, we evaluate the hypothesis that prolactin, one of the first hormones to change secretion pattern following mating, is involved in driving this suppression of physical activity levels during pregnancy. As part of the maternal adaptations to pregnancy, mice show a rapid, profound reduction in voluntary running wheel activity (RWA) as soon as pregnancy is achieved. ![]()
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