The higher brain centres involved with the processing of afferent baroreceptor information are poorly understood in humans. We have recently documented cortical neural activity patterns associated with the larger muscle sympathetic and heart rate responses elicited by moderate steady-state lower body negative pressure (LBNP) after exercise (1). The present study tested the hypotheses that: 1) the post-exercise recovery period modifies cortical activity patterns during the onset (baroreceptor unloading) and offset (baroreceptor reloading) phases of moderate LBNP, and 2) that this cortical network is associated with the functional integration of baroreceptor afferent information. Cortical activity was assessed using functional magnetic resonance imaging (fMRI) with blood oxygen level-dependent (BOLD) contrast in young healthy volunteers (n=11, 2♀/9♂). Continuous measures of cardiac stroke volume (SV) were collected separately (Doppler ultrasound). Repeated fMRI and laboratory tests were performed under control (no exercise) and following 1 hour of cycle ergometry exercise at ~60% of heart rate reserve. Cardiovascular and BOLD data were collected at baseline and during 4 repeated 45-s bouts of moderate (-35 mm Hg) LBNP separated by 30-s rest periods. A mild (-5 mm Hg) level of LBNP served as a control task. Significant changes (P < 0.005, uncorrected) in cortical BOLD signal were determined by a mixed effects ANOVA using the Statistical Parametric Mapping software package (SPM2). Compared to -5 mm Hg LBNP, moderate LBNP elicited larger (P < 0.05, 2-way ANOVA) reductions in SV after exercise (-26 ± 10 mL vs. -41 ± 8 mL, Mean ± S.D.). In both conditions, LBNP onset produced an increase in BOLD signal within the caudate body, pulvinar thalamic nucleus and Precuneus. However, BOLD signal increases during LBNP onset were greater in the caudate body, pulvinar thalamic nucleus, anterior cingulate, Precentral and Postcentral gyri after exercise. Common sites of cortical activation during LBNP offset were observed in the right insular cortex, cingulate and medial frontal gyri. Furthermore, the post-exercise recovery period elicited larger BOLD signal changes in the ventral lateral thalamic nucleus, caudate tail and inferior frontal gyrus during this period of baroreceptor reloading. We have highlighted the involvement of a discrete cortical network associated with post-exercise differences in baroreceptor loading/unloading stimulus profiles. These findings may facilitate our current understanding of the higher brain regions involved with the integration of baroreceptor afferent sensory signals versus those associated with the generation of baroreflex-mediated efferent autonomic and cardiovascular responses.
University of Leeds (2008) Proc Physiol Soc 10, PC46
Poster Communications: The post-exercise recovery period affects dynamic baroreceptor-related cortical activation patterns in humans.
D. S. Kimmerly1, S. W. Wong2, K. Shoemaker2
1. Medicine, The University Health Network, Toronto, Ontario, Canada. 2. Kinesiology, The University of Western Ontario, London, Ontario, Canada.
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Where applicable, experiments conform with Society ethical requirements.