[The characteristics of the motor activity of rat pups during the milk ejection reflex]

The motor activity of newborn rats sucking on anesthetized mothers was studied during the milk ejection reflex. When sucking before obtaining milk every 22 +/- 12 sec, newborn rats displayed an increased motor activity which lasted for 5 +/- 3 sec and coincided with the period of high-amplitude fluctuations of the pressure exerted on the nipple. The periods (5-10 sec) of increased motor activity were observed simultaneously in two or more rats at intervals of 25-30 sec. Simultaneous activity of the newborn rats was most frequently observed 10-30 sec before reflex rise of milk pressure in the mammary gland. Factors regulating the milk ejection reflex in rats, are discussed.