Thermal control of mother-young contact in rats

Abstract

The factors involved in the control of nest bout duration by mother rats were analyzed. Disruption of prolactin or adrenocortical secretions halted the normal progressive decline in daily nesting time, but the behavioral effects of hormone disruption were not mediated by a suppression of milk delivery. Rather, these hormones stimulate a chronic elevation in the body temperature of mother rats which makes mothers vulnerable to the acute thermal consequences of huddling with their litter. The temperature of a mother rat rises further after her ability to dissipate heat decreases when she comes in contact with her young, a rise that eventually limits the duration of nest bouts. Decreasing the efficiency of heat dissipation during nest bouts by elevating room temperature, pup temperature, or by removing the tail (a major pathway for heat dissipation) decreased nest bout duration. Increasing the rate of maternal heat loss by decreasing room temperature, pup temperature, or by partially removing the insulating fur of dams increased nest bout duration. We conclude that nest bouts are normally limited by a rise in maternal temperature, and that the rate of temperature rise determines the duration of each bout.