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1 Department of Internal Medicine, University of California, Davis, Davis, CA, USA
* To whom correspondence should be addressed. E-mail: naohayashi{at}ans.hss.osaka-u.ac.jp.
It was investigated whether exercising muscle mediates I investigated whether muscular contraction evoked cardiorespiratory increases (exercise pressor reflex) in alpha-chloralose and chloral hydrate anesthetized, pre-collicular, mid-collicular and post-collicular decerebrated rats. Mean arterial pressure (MAP), heart rate (HR) and minute ventilation (VE) were recorded before and during one-minute sciatic nerve stimulation, which induced static contraction of the triceps surae muscles, and during one-minute stretch of the calcaneal tendon, which selectively stimulated mechanosensitive receptors in the muscles. Anesthetized rats showed various patterns of MAP response to both stimuli, i.e., bi-phasic, depressor, pressor, and no responses. Sciatic nerve stimulation to muscle in pre-collicular decerebrated rats always evoked spontaneous running, so the exercise pressor reflex was not determined from these preparations. None of the post-collicular decerebrated rats showed either an MAP response or spontaneous running. Mid-collicular decerebrated rats consistently showed bi-phasic blood pressure response to both stimulations. The increases in MAP, HR and VE were related to the tension developed. The static contractions in mid-collicular decerebrated rats (381±65g developed tension) significantly increased MAP, HR and VE from 103±12 to 119±24mmHg, 386±30 to 406±83 bpm, and 122±7 to 133±25 ml/min, respectively. After paralysis, sciatic nerve stimulation had no effect on mean arterial pressure, MAP, HR or VE . These results indicate that mid-collicular decerebrated rat can be a model for the study of the exercise pressor reflex.
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