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The purpose of this study was to develop a dynamic exercise model in the rat that could be used to study central nervous system control of the cardiovascular system. Rats of both sexes were decerebrated under halothane anesthesia and prepared for induced locomotion on a freely turning wheel. Electrical stimulation of the mesencephalic locomotor region (MLR) elicited locomotion at different speeds and gait patterns and increased heart rate and blood pressure. Two maneuvers were performed to illustrate the potential use of the preparation. The first maneuver consisted of muscular paralysis, which prevents excitation of muscle mechanoreceptors and chemoreceptors resulting from exercise. MLR stimulation still increased blood pressure. The second maneuver was performed to determine whether the blood pressure response obtained during paralysis was an artifact of electrical stimulation of the MLR. After microinjection of gamma-aminobutyric acid into the MLR, electrical current thresholds for blood pressure and locomotion increased in parallel. gamma-Aminobutyric acid injection also reduced the pressor response to suprathreshold electrical stimulation by 76%. The injection results suggest that electrical stimulation of the MLR activates cells rather than fibers of passage. The blood pressure response of the exercise model is probably not an artifact of stimulation. The decerebrate rat locomotor preparation should offer another approach to investigate difficult problems in exercise physiology.
Bedford et al. (1992) studied this question.