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1 Kinesiology, University of Western Ontario, London, Canada
2 Advanced Imaging Laboratories, Robarts Research Institute, University of Western Ontario, London, Canada
3 Kinesiology, University of Western Ontario, London, Canada; Department of Physiology and Pharmacology, London, Canada
* To whom correspondence should be addressed. E-mail: kshomak{at}uwo.ca.
Generally, women demonstrate smaller cardiovascular reactions to stress, compared to men, but the mechanism of this difference is unknown. Recently, we identified a cortical network associated with cardiovascular responses to baroreceptor unloading in men. The current investigation examined whether differences in the activity patterns within this network were related to sex-related physiologic responses to lower body negative pressure (LBNP, 5, 15 and 35 mmHg). Forebrain activity in men and women (n = 8) was measured using functional magnetic resonance imaging with blood oxygen level-dependent (BOLD) contrast. Stroke volume (SV), heart rate (HR) and muscle sympathetic nerve activity (MSNA) were collected seperately. Men had larger decreases in SV (p < 0.01) during 35 mmHg LBNP only. At 35 mmHg LBNP, HR increased more in males then females (9 ± 1 beats.min-1 vs. 4 ± 1 beats.min-1, p < 0.05). Compared with women, increases in total MSNA were similar at 15 mmHg LBNP but greater during 35 mmHg LBNP in men (1067 ±123 vs. 658 ±103 a.u., p <0.05). BOLD signal changes (p< 0.005) were identified within forebrain regions associated with these sex-specific HR and MSNA responses. Men had larger increases in BOLD signal within the right insula and dorsal anterior cingulate cortex than women. Furthermore, men demonstrated greater BOLD signal reductions in the right amygdala, left insula, ventral anterior cingulate and ventral medial prefrontal cortex versus women. The greater changes in forebrain activity in men may have contributed to the elevated HR and sympathetic responses observed during 35 mmHg LBNP.
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