Effects of hypothalamic lesions on the cardiorespiratory responses to muscular contraction.

Recent studies have suggested that descending central command from a hypothalamic site (subthalamic locomotor region) is involved in the control of the respiratory and cardiovascular systems during exercise. The purposes of this study were to determine if this hypothalamic area provides tonic drive to the cardiorespiratory systems and modulates the cardiorespiratory responses to static muscular contraction. Anesthetized cats were studied before and after bilateral electrolytic lesioning of the subthalamic locomotor region. Muscular contraction was evoked by stimulation of the L7-S1 ventral roots. Bilateral hypothalamic lesions produced a fall in resting levels for respiratory frequency, minute ventilation, heart rate and arterial pressure. The lesions did not alter the significant increases in arterial pressure and minute ventilation produced by muscular contraction. However, larger heart rate and respiratory frequency responses to muscular contraction occurred post-lesion. We conclude that this area of the hypothalamus provides tonic drive to the cardiorespiratory systems. Furthermore, the subthalamic locomotor region may participate in the modulation of some cardiorespiratory responses to neural feedback from contracting muscles.