Anoxia in the newborn rat

A technique was developed for studying the effect of anoxia in the newborn rat with particular reference to persistence of electrical activity in the heart. In contrast to previous investigations in this field, no drastic surgical procedures were used, and the animals were held in a relatively undisturbed state in a closed temperature regulated chamber which could be filled with a gas mixture of any desired composition. Eleven newborn rats could be placed in the chamber at the same time under the same conditions, and electrocardiographic recordings could be obtained simultaneously from four animals at a time. Anoxia was produced by flushing and filling the chamber with tank nitrogen (99.9% N₂), and the period of persistence of electrocardiographic activity was determined taking as endpoint the last recorded electrical potential from the heart. Two hundred and thirty-two rats were used, ranging in age from three hours to eight days postnatal. The results obtained agree substantially with those reported by other workers using cruder methods. The "survival time" of electrocardiographic activity in the four day old group was only half that observed in newborn rats less than twelve hours postnatal, the difference being highly significant. However, there was no further significant change in "survival time" during the period from four to eight days. The technique developed should prove useful in studying many problems of neonatal physiology.Medicine, Faculty ofCellular and Physiological Sciences, Department ofGraduat