Thermoregulatory and maternal nestbuilding in Syrian hamsters: Interaction of ovarian steroids and energy demand

Abstract

To investigate the relationship between energy demand, ovarian hormones, and behavioral thermoregulation, we measured nestbuilding of female Syrian hamsters ( Mesocricetus auratus) under conditions where energy demand and circulating ovarian hormone levels varied. Hamsters increased nestbuilding under conditions of chronically elevated estradiol and progesterone levels (late gestation; ovariectomized animals treated with estradiol ± progesterone) and increased energy demand (late gestation or cold exposure). When hormone treatments were withdrawn, hamsters gained weight and reduced nestbuilding activity. Nestbuilding was not affected by lactation (characterized by low ovarian steroid levels and high energy demand), or by estrous cycle phase (characterized by relatively transient changes in ovarian steroid levels and subtle changes in energy demand). Thus, nestbuilding in Syrian hamsters was responsive to increased energy demand from cold exposure, late gestation, and to ovarian hormones. However, during lactation and estrous cycles, nestbuilding did not always change predictably according to known changes in energy expenditure and steroid hormone levels. Thus, levels of nestbuilding are influenced by factors in addition to ovarian hormones and energy expenditure under some circumstances.