[Study of cardiac, respiratory, and motor activity in rat fetuses]

Development of the cardiac, respiratory, and motor activity was studied in rat fetuses with preserved placenta circulation was studied at the 16th, 18th, and 20th gestation days. The presence of three main movement types has been found: complexes of generalization activity, local movements, and jerks. In development of respiratory function, there is observed a gradual transition from individual inspirations to series of respiratory movements and then to formation of periodic respiration episodes. At the studied period, the heart rate has been found to increase. The existence of the slow-wave modulations it the heart rate with a period of 20-40 s has been revealed. Analysis of interrelations between the respiratory and motor systems has shown that in the 16-day fetuses, each respiratory 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.