Study of cardiac, respiratory, and motor activities in rat fetuses

Development of the cardiac, respiratory, and motor activities in rat fetuses with preserved placental circulation was studied at the 16th, 18th, and 20th gestation days. The presence of three main movement types has been found: complexes of generalized activity, local movements, and jerks. In development of respiratory function, there is observed a gradual transition from individual inspirations to series of breathing movements and then to formation of periodic breathing episodes. At the studied period, the heart rate has been found to increase. The existence of the slow-wave modulations of the heart rate with a period of 2040 s has been revealed. Analysis of interrelations between the respiratory and motor systems has shown that in the 16-day fetuses, each breathing movement is accompanied by extensor jerk. By the 20th days of embryonic development (E20), uncoupling of the respiratory and motor activities occurs. Comparison of the activity observed in the cardiac and somatomotor systems has shown that at E16, the cardiac rhythm fluctuations do not depend on the motor excitation jerks. In the 18-day fetuses, brief slowing down (decelerations) of the cardiac rhythm appeared during the motor activity jerks, whereas at E20, on the contrary, an increase of frequency (accelerations) of the cardiac rhythm occurred.