Fig. 1

Cardiac sympathetic nerve activity changes elicited by acupuncture-like stimulation of a hindlimb during hypercapnia. a Upper traces sample recordings of cardiac sympathetic nerve activity. Lower traces recordings of nerve activity expressed as a histogram of impulses per 5 s. Acupuncture-like stimulation was applied for 1 min as indicated by the bar below each trace. b Summary of basal nerve activity during hypercapnia. c, d Summary of responses of cardiac sympathetic nerve activity. c Changes in nerve activity in the 10-s period just before the end of the acupuncture-like stimulation were expressed as a percentage of the pre-stimulus basal values for the 10-s period. d The cardiac sympathetic nerve responses under control conditions \( (F_{{{\text{ET}_{\text{CO}}}_{ 2} }} 3.0\% ) \) were taken as 100%. Each point or column and vertical bar depicts the mean ± SEM for 6 rats. For each rat, the results of 3 trials were averaged. *p < 0.05, **p < 0.01; significantly different from the magnitudes of the responses under control conditions \( (F_{{{\text{ET}_{\text{CO}}}_{ 2} }} 3.0\% ) \) using one-way repeated measures ANOVA followed by Dunnett’s multiple comparison test. The background noise level of nerve recording was about 10 μV when checked at the end of the experiment (after the rat had been killed)