Maternal thermal stimulation changes metabolic activity in fetal hypothalamus

To study whether the central nervous system in the perinatal fetal rat can operate during maternal cooling and warming, we examined the 2-deoxy-D-[14C]glucose ([14C]DG) uptake in the fetal brain. Full-term pregnant rats were placed at three different ambient temperatures of 35-37 degrees C, 24-25 degrees C and 0-10 degrees C. Saline containing 20 microCi/100 g of [14C]DG was injected into the superior caval vein in the pregnant rats. Forty-five min after the injection, the mother rats were decapitated and the fetal brains were taken out for autoradiography. The [14C]DG uptake was significantly influenced by maternal thermal stimulation in the hypothalamus and not in other brain regions examined such as the cerebral cortex, the basal ganglia and the limbic nuclei. Glucose utilization in the fetal anterior hypothalamus, paraventricular hypothalamus and dorsomedial hypothalamus significantly increased when the mother rat was exposed to heat compared to when the mother rat was in the thermoneutral condition. During maternal cooling, glucose utilization in the ventromedial hypothalamus and dorsomedial hypothalamus significantly decreased. There was no area activated by cooling and/or inhibited by warming. Compared to a similar study in adult rats (Am. J. Physiol., 248 (1985) R84-92), the present results suggest that although the perinatal fetal brain does not respond to thermal stimulation in terms of glucose utilization as fully as the adults, a few hypothalamic nuclei have already acquired thermal responses, which might be a possible neuronal basis for the thermoregulatory responses just after birth in rats.