Submitted on January 12, 2007
Accepted on March 4, 2007
Forebrain regions associated with post-exercise differences in autonomic and cardiovascular function during baroreceptor unloading
Derek S. Kimmerly1, Savio W Wong1, Deb Salzer1, Ravi Menon2, and J. Kevin Shoemaker1*
1 School of Kinesiology, Neurovascular Res. Lab., The University of Western Ontario, London, Canada
2 Advanced Imaging Labs, Robarts Research Institute, The University of Western Ontario, London, Canada
* To whom correspondence should be addressed. E-mail: kshoemak{at}uwo.ca.
The cortical regions representing peripheral autonomic reactions in humans are poorly understood. This study examined whether changes in forebrain activity were associated with the altered physiologic responses to lower body negative pressure (LBNP) following a single bout of dynamic exercise (POST-EX). We hypothesized that, compared with the non-exercised condition (NO-EX), POST-EX would elicit greater reductions in stroke volume (SV) and larger increases in heart rate (HR) and muscle sympathetic nerve activity (MSNA) during LBNP (5-, 15- and 35-mmHg). Forebrain neural activity (n=11) was measured using blood oxygen level-dependent (BOLD) functional magnetic resonance imaging. HR, SV, arterial blood pressure (ABP) and MSNA were collected separately. Compared with NO-EX, baseline ABP was reduced while HR and TVC were elevated in POST-EX (P < 0.05). In both conditions, 5-mmHg LBNP did not elicit a change (from baseline) in any physiologic parameter. Compared with NO-EX, 35-mmHg LBNP-mediated decreases in SV and TVC produced greater increases in HR and MSNA during POST-EX (P < 0.05). The right posterior insula and dorsal anterior cingulate cortex demonstrated a larger decrease in BOLD at 5-mmHg LBNP but greater BOLD increase at 15- and 35-mmHg LBNP POST-EX versus NO-EX (P < 0.005). Conversely, the thalamus and ventral medial prefrontal cortex displayed the opposite BOLD activity pattern (i.e., larger increase at 5-mmHg LBNP but greater decrease at 15- and 35-mmHg LBNP, POST-EX versus NO-EX). Our findings suggest that discrete forebrain regions may be involved with the generation of baroreflex-mediated sympathetic and cardiovascular responses elicited by moderate LBNP.
