Suprapontlne Contributions to the Carotld Sinus Reflex in the Cat

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Abstract
Carotid sinus reflex response was measured before and after decerebration in 27 cats with and without the vagus nerves intact. Body temperature, central venous pressure, arterial oxygen saturation, PCO2 and pH were kept within normal limits. The anesthetized animals were uniformiy subjected to a wide range of controlied sirius pressure changes in each condition. A mathematical analog with four parameters was empioyed to relate carotid sinus pressure to systemic arterial pressure. The expression takes the form of a logistic curve, describes the reflex response with an accuracy of 98%, and provides a design in which errors are normally distributed for statistical testing of differences in parameters occurring with experimental intervention. The major effect on the sinus reflex of brainstem transection at the collicular level was a decrease in the effective range over which arterial pressure could be varied by changes in sinus pressure. Although a given change in sinus pressure in the median range of 70 to 100 mm Hg produced a proportional change in arterial pressure, transection markedly decreased reflex responses to lower sinus pressures. It was concluded that a transection at the coflicular level may not significantly change mean systemic pressure, but it does decrease the animal's ability to adjust to variations in arterial pressure. The data lend credence to the hypothesis that supramedullary areas can and do function in directing autonomic activity during the carotid sinus reflex.