The overall aim of the experiments proposed in this application is to determine whether dynamic exercise differentially affects the discharge of group III and IV muscle afferents. Exercise will be induced in decerebrate unanesthetized cats by electrical and chemical stimulation of the mesencephalic locomotor region. The effects of various levels of exercise and ischemia on the discharge of the group III and IV muscle afferents will be determined. Particular attention will be paid to afferent's responses to post-exercise circulatory occlusion, a """"""""pure"""""""" metaboreflex stimulus. Attention will also be paid to the role played by cyclooxygenase metabolites and bradykinin in stimulating these afferents during dynamic exercise. Finally, the proposed experiments will examine the effect of muscular fatigue on the responses of group III and IV afferents to exercise. These thin fiber afferents have been hypothesized to be responsible for the reflex inhibition of alpha motoneurons during fatiguing muscular contractions in humans. The autonomic and ventilatory response to dynamic exercise are well established and include increases in sympathetic discharge influencing the vasculature, heart rate, contractility, breathing frequency and tidal volume. The neural mechanisms causing these increases are controversial. The experiments proposed in this application will determine the mechanical and metabolic stimuli to these afferents during exercise.
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