GABA in nucleus tractus solitarius participates in electroacupuncture modulation of cardiopulmonary bradycardia reflex

Abstract

Tjen-A-Looi SC, Guo ZL, Longhurst JC. GABA in nucleus tractus solitarius participates in electroacupuncture modulation of cardiopulmonary bradycardia reflex. Am J Physiol Regul Integr Comp Physiol 307: R1313-R1323, 2014. First published September 17, 2014 doi:10.1152/ajpregu.00300.2014 stimulates cardiopulmonary receptors and cardiovascular reflex responses, including decreases in blood pressure and heart rate mediated by the brain stem parasympathetic cardiac neurons in the nucleus ambiguus and nucleus tractus solitarius (NTS). Electroacupuncture (EA) at P5-6 stimulates sensory fibers in the median nerve and modulates these reflex responses. Stimulation of median nerves reverses bradycardia through action of ␥-aminobutyric acid (GABA) in the nucleus ambiguus, important in the regulation of heart rate. We do not know whether the NTS or the neurotransmitter mechanisms in this nucleus participate in these modulatory actions by acupuncture. We hypothesized that somatic nerve stimulation during EA (P5-6) modulates cardiopulmonary inhibitory responses through a GABAergic mechanism in the NTS. Anesthetized and ventilated cats were examined during either PBG or direct vagal afferent stimulation while 30 min of EA was applied at P5-6. Reflex heart rate and blood pressure responses and NTS-evoked discharge were recorded. EA reduced the PBG-induced depressor and bradycardia reflexes by 67% and 60%, respectively. Blockade of GABA A receptors in the NTS reversed EA modulation of bradycardia but not the depressor response. During EA, gabazine reversed the vagally evoked discharge activity of cardiovascular NTS neurons. EA modulated the vagal-evoked cardiovascular NTS cellular activity for 60 min. Immunohistochemistry using triple labeling showed GABA immunoreactive fibers juxtaposed to glutamatergic nucleus ambiguus-projecting NTS neurons in rats. These glutamatergic neurons expressed GABA A receptors. These findings suggest that EA inhibits PBG-evoked bradycardia and vagally evoked NTS activity through a GABAergic mechanism, likely involving glutamatergic nucleus ambiguus-projecting NTS neurons. vagal excitation; phenylbiguanide; glutamic acid CLINICAL AND EXPERIMENTAL STUDIES suggest that acupuncture reduces hypertension, hypotension, and myocardial ischemia (4,11,37,41,42,51). Modulation of cardiovascular function and elevated sympathetic activity is effective with low frequency and voltage stimulation of electroacupuncture (EA) at specific acupoints P5-6 positioned to activate the underlying median nerves (44 -46). Bilateral stimulation of P5-6 acupoints activates thinly myelinated and unmyelinated sensory fibers in the median nerve and neural pathways that project to cardiovascular-related regions in the central nervous system, which regulate autonomic activity and hence hemodynamic responses (21,23,39). Nuclei in the hypothalamus, midbrain, and medulla process this somatic input during EA to modulate sympathoexcitatory reflex responses (26,28,43). Several neurotransmitter systems, including opioids and ␥-aminobutyric...

Paraventricular Nucleus Modulates Excitatory Cardiovascular Reflexes during Electroacupuncture

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