Localization of central cardiovascular control mechanism in lower brain stem of the cat

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Abstract
The lower brain stems of 42 vagotomized, midcollicular decerebrate cats under chloralose anesthesia were explored for vasomotor and cardiac responses by means of the stereotaxic technique. When a stimulus was given through bipolar coaxial electrodes with minute exposures at the tips, it was found possible to localize these responses in very discrete areas in the dorsal reticular formation and the adjacent periventricular gray. With current of slightly higher intensity, comparable responses could also be obtained in the ventrolateral reticular formation. It is suggested that the latter constitutes the hypothalamic efferent pathways, while responses from the dorsal medulla signal the activation of the bulbar pressor and cardioaccelerator mechanism. Further, pressor responses from the medulla on the right side are very often accompanied by marked cardioacceleration and only slight or moderate augmentation of cardiac contractions, whereas those from the left are accompanied by marked augmentation and moderate cardioacceleration. This finding suggests that the medullary sympathetic system descends predominately in the spinal cord of the homolateral side.