Identifying the Neurocircuitry Involved in the Exercise Pressor Reflex during Exercise in Humans

Abstract

The neurocircuitry responsible for the muscle pressor reflex in humans remains incompletely identified. Group III and IV afferents carry sensory information regarding this reflex, although central integration is still poorly defined. Emerging evidence reports that the periaqueductal grey (PAG) in humans could be a major site for controlling the cardiovascular response to exercise. We assessed the spectral changes in local field potentials (LFPs) recorded from deep brain nuclei in patients who had undergone neurosurgery for movement or pain disorders. Patients with electrodes implanted were asked to perform light handgrip exercise, followed by arterial occlusion of the exercised limb in order to maintain the pressor response. We focussed on the PAG, and compared it to control areas, i.e. the internal globus pallidus (GPi) and thalamus. The PAG showed significant increases in LFP power at frequencies from 0‐100Hz (p<0.001) during occlusion. This period was associated with maintained elevated arterial blood pressure. Cuff inflation without prior exercise resulted in a small increase in PAG activity suggesting that the inflation itself may, in part, contribute to the pressor response associated with occlusion. No change in GPi or thalamus activity was observed during occlusion. These data suggest the PAG is a part of the subcortical neurocircuitry involved in the exercise pressor reflex.