Medullary substrate and differential cardiovascular responses during stimulation of specific acupoints

Abstract
Electroacupuncture (EA) at P5–P6 acupoints overlying the median nerve reduces premotor sympathetic cardiovascular neuronal activity in the rostral ventral lateral medulla (rVLM) and visceral reflex pressor responses. In previous studies, we have noted different durations of influence of EA comparing P5–P6 and S36–S37 acupoints, suggesting that point specificity may exist. The purpose of this study was to evaluate the influence of stimulating P5–P6 (overlying the median nerve), LI4–L7 (overlying branches of the median nerve and the superficial radial nerve), LI6–LI7 (overlying the superficial radial nerve), LI10–LI11 (overlying the deep radial nerves), S36–S37 (overlying the deep peroneal nerves), or K1–B67 (overlying terminal branches of the tibial nerves) specific acupoints, overlying deep and superficial somatic nerves, on the excitatory cardiovascular reflex and rVLM responses evoked by stimulation of chemosensitive receptors in the cat's gallbladder with bradykinin (BK) or direct splanchnic nerve (SN) stimulation. We observed point-specific differences in magnitude and duration of EA inhibition between P5–P6 or LI10–LI11 and LI4–L7 or S36–S37 in responses to 30-min stimulation with low-frequency, low-current EA. EA at LI6–LI7 and K1–B67 acupoints as well as direct stimulation of the superficial radial nerve did not cause any cardiovascular or rVLM neuronal effects. Cardiovascular neurons in the rVLM, a subset of which were classified as premotor sympathetic cells, responded to brief (30 s) stimulation of the SN as well as acupoints P5–P6, LI10–LI11, LI4–L7, S36–S37, LI6–LI7, or K1–B67, or underlying somatic pathways in a fashion similar to the reflex responses. In fact, we observed a significant linear relationship ( r 2 = 0.71) between the evoked rVLM response and reflex change in mean arterial blood pressure. In addition, EA stimulation at P5–P6 and LI4–L7 decreased rVLM neuronal activity by 41 and 12%, respectively, for >1 h, demonstrating that prolonged input into the medulla during stimulation of somatic nerves, depending on the degree of convergence, leads to more or less inhibition of activity of these cardiovascular neurons. Thus EA at acupoints overlying deep and superficial somatic nerves leads to point-specific effects on cardiovascular reflex responses. In a similar manner, sympathetic cardiovascular rVLM neurons that respond to both visceral (reflex) and somatic (EA) nerve stimulation manifest graded responses during stimulation of specific acupoints, suggesting that this medullary region plays a role in site-specific inhibition of cardiovascular reflex responses by acupuncture.