CARDIOVASCULAR-RESPONSES DURING SPONTANEOUS OVERGROUND LOCOMOTION IN FREELY MOVING DECEREBRATE CATS

To examine whether the cerebrum is essential for producing the rapid c ardiovascular adjustment at the beginning of overground locomotion, we examined heart rate (HR), mean arterial blood pressure (MAP), and int egrated electromyogram (iEMG) of the forelimb triceps brachialis muscl e in freely moving decerebrate cats during locomotion. Two to four day s after decerebration surgery performed at the level of the precollicu lar-premammillary body, the animals spontaneously produced coordinated overground locomotion, supporting body weight. HR began to increase i mmediately before the onset of iEMG, and MAP began to rise almost simu ltaneously with the iEMG onset. Their increases in HR and MAP (24 +/- 3 beats/min and 22 +/- 4 mmHg) were sustained during locomotion. Sinoa ortic denervation (SAD) did not affect the abrupt changes in HR and MA P at the beginning of locomotion (0-4 s from the onset of iEMG), where as SAD had a contrasting effect during the subsequent period, a decrea se in the HR response (9 +/- 1 beats/min) and an increase in the MAP r esponse (30 +/- 3 mmHg). These results suggest that the cerebrum and t he rostral part of the diencephalon are not essential for producing th e rapid cardiovascular adjustment at the beginning of spontaneous over ground locomotion. The arterial baroreflex does not contribute to this rapid adjustment but plays an important role in regulating the cardio vascular responses during the later period of spontaneous locomotion.