Sympathetic nerve activity during deep brain stimulation

Electrical ‘deep brain’ stimulation (DBS) in humans has previously been shown to alter cardiovascular parameters such as blood pressure, pulse pressure and the response of blood pressure to standing. An alteration in the autonomic nervous system is likely to be responsible for these changes. The aim of this study was to directly measure muscle sympathetic nerve activity (MSNA) in humans with electrodes simultaneously stimulating the periaqueductal grey (PAG) and other areas known to modulate arterial blood pressure. MSNA has been successfully recorded in nine patients with electrodes in the PAG (n=4) and the subthalamic nucleus (STN) (n=5). Our preliminary results show, that when stimulating the PAG, the occurrence of sympathetic bursts remained unchanged, while the burst amplitude distribution demonstrated a transfer from low amplitude bursts towards a greater number of medium to high amplitude bursts during stimulation. Blood pressure variability changed in parallel with changes in MSNA. Stimulation of the STN resulted in unchanged burst amplitude distribution, whereas the occurrence of sympathetic bursts changed, which was paralleled by alterations in blood pressure and heart rate. Evidence of a differentiated control of occurrence and strength of sympathetic bursts has been reported previously. While it is not known how the differentiated control of sympathetic bursts is brought about, it has been suggested that the baroreflex modulation of sympathetic outflow occurs at two CNS locations. Our preliminary results on the effects of DBS of the STN and PAG on efferent sympathetic nerve traffic are in line with previous findings of a differentiated control of occurrence and strength of sympathetic bursts. But importantly, as modulation of sympathetic outflow is vital in the regulation of arterial blood pressure, our results may shed light on cardiovascular central neurocircuitry responsible for cardiovascular modulation.