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1 Osaka University, Graduate School of Engineering Science, Toyonaka, Osaka, Japan
2 Osaka University, Graduate School of Engineering Science, Toyonaka, Osaka, Japan; Osaka University, School of Health and Sport Sciences, Toyonaka, Osaka, Japan
3 Kyushu University, Institute of Health Science, Kasuga, Fukuoka, Japan
* To whom correspondence should be addressed. E-mail: naohayashi{at}ihs.kyushu-u.ac.jp.
We compared sympathetic and circulatory responses between kidney and skeletal muscles during fictive locomotion evoked by electrical stimulation of mesencephalic locomotor region (MLR) in decerebrate and paralyzed rats (n=8). Stimulation of the MLR for 30 s at 40 µA current intensity significantly increased arterial pressure (+38 ± 6 mmHg), triceps surae muscles blood flow (+17 ± 3 %), and both renal and lumbar sympathetic nerve activities (RSNA: +113 ± 16 %, LSNA: +31 ± 7 %). The stimulation also significantly decreased renal cortical blood flow (-18 ± 6 %) and both renal cortical and triceps surae muscles vascular conductances (RCVC: -38 ± 5 %, TSMVC: -17 ± 3 %). The sympathetic and vascular conductance changes were significantly dependent on current intensity for stimulation between 20, 30, and 40 µA. The changes in LSNA and TSMVC were significantly less than those in RSNA and RCVC, respectively, at all current intensities. At the early stage of stimulation (0-10 s), the decreases in RCVC and TSMVC were significantly correlated with the increases in RSNA and LSNA, respectively. These data demonstrate that fictive locomotion induces less vasoconstriction in skeletal muscles than in the kidney due to less sympathetic activation. This suggests that a neural mechanism mediated by central command contributes to the blood flow distribution by evoking differential sympathetic outflow during exercise.
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