Paraventricular Nucleus Modulates Excitatory Cardiovascular Reflexes during Electroacupuncture.

Stephanie C Tjen-A-Looi,John C Longhurst,Zhi-Ling Guo,Liang-Wu Fu

doi:10.1038/srep25910

Stephanie C Tjen-A-Looi, John C Longhurst + Show 2 more

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https://doi.org/10.1038/srep25910

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Abstract

The paraventricular nucleus (PVN) regulates sympathetic outflow and blood pressure. Somatic afferent stimulation activates neurons in the hypothalamic PVN. Parvocellular PVN neurons project to sympathoexcitatory cardiovascular regions of the rostral ventrolateral medulla (rVLM). Electroacupuncture (EA) stimulates the median nerve (P5-P6) to modulate sympathoexcitatory responses. We hypothesized that the PVN and its projections to the rVLM participate in the EA-modulation of sympathoexcitatory cardiovascular responses. Cats were anesthetized and ventilated. Heart rate and mean blood pressure were monitored. Application of bradykinin every 10-min on the gallbladder induced consistent pressor reflex responses. Thirty-min of bilateral EA stimulation at acupoints P5-P6 reduced the pressor responses for at least 60-min. Inhibition of the PVN with naloxone reversed the EA-inhibition. Responses of cardiovascular barosensitive rVLM neurons evoked by splanchnic nerve stimulation were reduced by EA and then restored with opioid receptor blockade in the PVN. EA at P5-P6 decreased splanchnic evoked activity of cardiovascular barosensitive PVN neurons that also project directly to the rVLM. PVN neurons labeled with retrograde tracer from rVLM were co-labeled with μ-opioid receptors and juxtaposed to endorphinergic fibers. Thus, the PVN and its projection to rVLM are important in processing acupuncture modulation of elevated blood pressure responses through a PVN opioid mechanism.

Highlights

Electroacupuncture (EA) stimulation with low current and low frequency (2–4 mA, 2 Hz, 0.5 ms) decreases blood pressure and elevates plasma norepinephrine in patients with mild to moderate hypertension[1]
We have demonstrated that the long-lasting inhibitory effect of point specific EA on reflex induced elevated blood pressure is related to the modulation of cardiovascular neurons in the rVLM27,32
We currently show that EA reduces activity in the rostral ventrolateral medulla (rVLM) through an opioid mechanism in the paraventricular nucleus (PVN) that is rich in endorphinergic fibers and μ-opioid receptors

Summary

Introduction

Electroacupuncture (EA) stimulation with low current and low frequency (2–4 mA, 2 Hz, 0.5 ms) decreases blood pressure and elevates plasma norepinephrine in patients with mild to moderate hypertension[1]. We examined the possibility that stimulation of somatic afferents with acupuncture modulates PVN cardiovascular activity through an opioid mechanism. By activating μ-opioid receptors in the rVLM, inhibits sympathetic outflow and decreases sympathetic excitatory response induced by activation of visceral afferents with application of bradykinin (BK) on the gallbladder through activation of the splanchnic nerve[2,25]. Neurons that receive convergent input from afferents innervating the gallbladder, baroreceptors and median nerves have been shown to process EA-cardiovascular inhibition[26,27]. These rVLM neurons display prolonged inhibition lasting beyond the 30-min of EA stimulation at P5-P6 (sensitive to EA) and contribute to the reduction of sympathoexcitatory visceral cardiovascular responses. These data have been published in preliminary form[28]

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