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1Graduate School of Engineering Science and 2School of Health and Sport Sciences, Osaka University, Toyonaka, Osaka; and 3Institute of Health Science, Kyushu University, Kasuga, Fukuoka, Japan
Submitted 14 June 2005 ; accepted in final form 31 August 2005
We compared sympathetic and circulatory responses between kidney and skeletal muscles during fictive locomotion evoked by electrical stimulation of the 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 muscle 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 muscle vascular conductances (RCVC –38 ± 5%, TSMVC –17 ± 3%). The sympathetic and vascular conductance changes were significantly dependent on current intensity for stimulation at 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), decreases in RCVC and TSMVC were significantly correlated with increases in RSNA and LSNA, respectively. These data demonstrate that fictive locomotion induces less vasoconstriction in skeletal muscles than in kidney because of less sympathetic activation. This suggests that a neural mechanism mediated by central command contributes to blood flow distribution by evoking differential sympathetic outflow during exercise.
central command; mesencephalic locomotor region; sympathetic nervous system; renal blood flow; muscle blood flow
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