AUTONOMIC RESPONSES MEDIATED VIA THE CORTICOSPINAL TRACT

Abstract

Autonomic responses to medullary pyramidal tract stimulation were studied in 66 unanesthetized decerebrate cats. The pyramids were stimulated under direct vision and the stimulus intensities used were sufficient to produce vigorous, but not maximal movements of the contralateral limbs. Changes were recorded in autonomic nerves: sweating, blood pressure, pulse rate, bladder contraction, gastric antral contraction, nictitating membrane, pupils and piloerection. Patterns of response were variable and this was especially true in structures which showed a high degree of spontaneous activity. The general routine used to prove the relation of the autonomic responses to descending activity in the pyramidal tract was sectioning of the pyramid oral to the stimulating electrode and admn. of curare. Neither affected the response. Sectioning of the pyramid below the point of stimulation abolished the reaction. Subsequent to the latter section, stimulation below it or of the contralateral pyramid produced the response. It is concluded that the cerebral cortex can influence most autonomic functions by direct impingement in the spinal cord separately from the hypothalamus and its descending path. It is suggested that the predominant pyramidal effect on visceral structures is one of facilitation of activity patterns essentially detd. at spinal and peripheral levels.