Paraventricular Nucleus in Acupuncture's Inhibition of the Von Bezold Jarsich Reflex

Abstract

Electroacupuncture (EA) stimulates specific somatic sensory nerves underlying P5‐6 acupoints and modulates parasympathoexcitatory reflex responses through actions in the brainstem. Although Bezold Jarisch‐induced decreases in blood pressure and heart rate reflex responses are modulated by acupuncture through actions in nucleus tractus solitarius and nucleus ambiguus, the role of the hypothalamus is unclear. The paraventricular nucleus (PVN) regulates sympathetic outflow and blood pressure. Vagal afferent stimulation activates neurons in the PVN but little is known about cardiopulmonary physiological actions in this nucleus. We therefore hypothesized that the PVN participates in the Bezold Jarisch responses and EA modulation of parasympathoexcitatory cardiovascular responses. Rats were anesthetized, ventilated, and heart rate and mean blood pressures were monitored. Application of phenylbiguanide (PBG) every 10 min close to the right atrium induced consistent depressor and bradycardia reflex responses. Unilateral microinjection of kainic acid or kynurenic acid in the PVN reduced the reflex responses. Thirty min of bilateral EA at P5‐6 acupoints reduced the depressor and bradycardia responses lasted for >60 min. Unilateral inhibition of the PVN with 50 nl of naloxone reversed the EA‐inhibition during repeated PBG‐induced responses. EA‐related c‐Fos PVN neurons were juxtaposed to endorphinergic PVN fibers. Thus, cardiopulmonary PVN responses are important in processing acupuncture modulation of cardiovascular inhibitory reflexes.Funded by HL‐63313, HL‐72125.