title: Motor cortical disinhibition with baroreceptor unloading induced by orthostatic stress.
abstract: Unloading of the baroreceptors due to orthostatic stress increases corticospinal excitability. The purpose of this study was to examine the effects of baroreceptor unloading due to orthostatic stress on intracortical excitatory and inhibitory pathways in the motor cortex. With transcranial magnetic stimulation, measures of intracortical excitability for a hand muscle were tested on 2 days in healthy young adults. Lower body negative pressure (LBNP) of 40 mmHg was applied during one of the days and not during the Control day. During application of LBNP heart rate and the low-frequency component of heart rate variability increased, while mean arterial blood pressure was maintained. In the resting state, LBNP decreased short-interval intracortical inhibition (SICI) and had no effect on intracortical facilitation (ICF) or short-interval intracortical facilitation (SICF) compared with the Control day. During isometric contraction, no effects of LBNP were observed on tested measures of intracortical excitability including SICI, SICF, and cortical silent period. It was concluded that baroreceptor unloading due to orthostatic stress results in diminished intracortical inhibition, at least in the resting muscle.
authors.affiliation: School of Applied Physiology, Georgia Institute of Technology, Atlanta, Georgia;
authors.forename: Vasiliy E
authors.initials: VE
authors.lastname: Buharin
authors.affiliation: School of Applied Physiology, Georgia Institute of Technology, Atlanta, Georgia; Department of Physical Therapy, Georgia State University, Atlanta, Georgia; and Rehabilitation R&D Center of Excellence, Atlanta Department of Veterans Affairs Medical Center, Decatur, Georgia.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Butler
authors.affiliation: School of Applied Physiology, Georgia Institute of Technology, Atlanta, Georgia; Rehabilitation R&D Center of Excellence, Atlanta Department of Veterans Affairs Medical Center, Decatur, Georgia shinohara@gatech.edu.
authors.forename: Minoru
authors.initials: M
authors.lastname: Shinohara
mesh_terms: D001794:Blood Pressure / Q000502:physiology; D019054:Evoked Potentials, Motor; D005260:Female; D006225:Hand / Q000502:physiology; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D009434:Neural Pathways / Q000502:physiology; D011311:Pressoreceptors / Q000502:physiology*; D011712:Pyramidal Tracts / Q000502:physiology; D012146:Rest / Q000502:physiology; D013312:Stress, Physiological / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation; D015919:Ventilators, Negative-Pressure; D055815:Young Adult
keywords: autonomic nervous system; motor cortex; transcranial magnetic stimulation