Electroacupuncture Reduced Airway Inflammation by Activating Somatosensory–Sympathetic Pathways in Allergic Asthmatic Rats

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Electroacupuncture Reduced Airway Inflammation by Activating Somatosensory–Sympathetic Pathways in Allergic Asthmatic Rats

Electroacupuncture (EA) has been recognized as an effective treatment for various respiratory disorders, including asthma. However, the underlying mechanisms by which EA protects lung function remain poorly understood. This study aimed to explore the neuroanatomical mechanisms through which EA stimulation at the BL13 acupoint (Feishu) improves asthma symptoms. The findings reveal that EA reduces airway inflammation and mucus secretion by activating somatosensory–sympathetic pathways, providing a new explanation and clinical basis for the use of EA-BL13 in treating allergic asthma and other respiratory disorders.

Introduction

Acupuncture, a traditional Chinese medicine practice, has been shown to reduce airway inflammation and improve lung function in respiratory disorders. Although the physical presence of meridian channels has not been proven, contemporary studies suggest that somatosensory–autonomic pathways may explain the functional connections between somatic regions and internal organs. Somatic stimulation activates primary sensory neurons, which transmit sensory information from the spinal cord to the brain or subsequent spinal neurons, thereby activating the autonomic nervous system. Previous studies have demonstrated that EA stimulation initiates vagal or sympathetic efferent pathways to inhibit systemic inflammation.

The lung is innervated by both sympathetic and parasympathetic nerves. The sympathetic nervous system causes the relaxation of bronchial smooth muscle and inhibits mucus secretion, while the parasympathetic system has the opposite effect. Sympathetic preganglionic neurons (SPNs) are located in the intermediolateral (IML) nuclei of the spinal cord and send postganglionic fibers to the sympathetic trunk. Catecholamines released from these fibers target adrenergic receptors (ARs), which are involved in bronchodilation and inflammatory responses.

Asthma is a chronic airway inflammatory disease affecting over 350 million people worldwide. Despite available treatments, more than half of asthma patients do not achieve adequate symptom control. Previous studies have suggested that acupuncture is effective in treating allergic asthma. This study used an ovalbumin (OVA)-induced allergic asthma model to investigate the neuroanatomical mechanisms of EA-BL13 in improving asthma symptoms.

Methods

Animals and Experimental Design

Male Sprague-Dawley rats (180–200 g) were used in this study. All experiments followed the principles of the Regulation for Administration of Affairs Concerning Experimental Animals (China) and were approved by the Institutional Animal Care and Use Committee of China-Japan Friendship Institute of Clinical Medical Sciences. Rats were randomly divided into four groups: sham, sham + preEA, asthma, and asthma + preEA. Another set of rats was divided into four groups to assess the effect of EA after OVA induction: sham, sham + postEA, asthma, and asthma + postEA.

OVA-Induced Allergic Asthma Model

Allergic asthma was induced by intranasal 2.0% OVA instillation combined with intraperitoneal injection of 10.0% OVA. Sham rats received phosphate-buffered saline (PBS) instead of OVA. Rats were euthanized 24 hours after the final OVA challenge, and bronchoalveolar lavage fluid (BALF) was collected for inflammatory cell counting and cytokine analysis.

EA Treatment

EA treatment was administered at the BL13 acupoint to anesthetized rats. The acupoint was stimulated at an intensity of 3.0 mA and a frequency of 4.0 Hz for 30 minutes. Sham groups received needle insertion without electrical stimulation. To study the effects of EA-BL13 on OVA-induced inflammation, EA was performed either before or after OVA induction.

Immunofluorescent Staining

After euthanasia, tissues including the dorsal root ganglia (DRG), spinal cord, brain, sympathetic trunk, and lung were collected for immunofluorescent staining. The intensity of phosphorylated extracellular regulated protein kinases (p-ERK) and the expression of c-FOS, a marker of neuronal excitation, were measured in various tissues.

Enzyme-Linked Immunosorbent Assay (ELISA)

The levels of interleukin (IL)-4, IL-5, noradrenaline (NE), adrenaline (E), and cyclic adenosine monophosphate (cAMP) were measured using ELISA kits. BALF was collected for IL-4 and IL-5 measurements, while blood and lung tissues were collected for NE and E measurements.

Histological Staining

Lung tissues were stained with hematoxylin and eosin (H&E) and periodic acid-Schiff (PAS) to evaluate inflammatory cell infiltration and mucus secretion.

Real-Time Polymerase Chain Reaction (PCR)

The expression levels of adrenergic receptors (ARs) and protein kinase A (PKA) subunits were quantified using real-time PCR.

Results

PreEA-BL13 Ameliorated Bronchial Inflammation and Mucus Secretion

PreEA-BL13 significantly reduced the number of inflammatory cells (leukocytes, neutrophils, lymphocytes, and eosinophils) and the levels of IL-4 and IL-5 in BALF compared to the asthma group. H&E and PAS staining showed that preEA-BL13 alleviated inflammatory cell infiltration and decreased the number of goblet cells in lung tissue.

EA at the BL13 Acupoint Activated Somatosensory–Sympathetic Pathways

EA-BL13 increased the expression of p-ERK in primary sensory neurons in the thoracic DRG and c-FOS in neurons in the dorsal horn of the spinal cord, indicating the activation of the somatosensory system. EA-BL13 also induced c-FOS in SPNs and the sympathetic trunk, suggesting the activation of sympathetic pathways. Fluoro-Ruby injection confirmed that neurons in the dorsal horn of the spinal cord provide synaptic input to thoracic SPNs.

EA at the BL13 Acupoint Suppressed OVA-Induced Bronchial Inflammation via Sympathetic Nerve Excitation

Pharmacological extirpation of sympathetic nerves using 6-hydroxydopamine hydrobromide (6-OHDA) abolished the anti-inflammatory effects of preEA-BL13, confirming that sympathetic nerve excitation is essential for EA-BL13’s therapeutic effects.

β2AR Expression in T Cells Was Indispensable in the Mitigative Effect of PreEA-BL13

Real-time PCR and immunofluorescent staining showed that preEA-BL13 significantly increased the expression of β2AR in T cells. Blocking β2AR with ICI118,551 reversed the anti-inflammatory effects of preEA-BL13, indicating that β2AR on T cells is crucial for EA-BL13’s therapeutic effects.

β2AR-Mediated cAMP/PKA Signaling Pathway Was Activated by PreEA-BL13 Stimulation

PreEA-BL13 increased the levels of cAMP and the expression of PKA subunits in lung tissue. Blocking PKA with H89 reversed the anti-inflammatory effects of preEA-BL13, confirming that the β2AR-mediated cAMP/PKA pathway is essential for EA-BL13’s therapeutic effects.

PostEA-BL13 Alleviated Bronchial Inflammation and Mucus Secretion

PostEA-BL13, performed after OVA induction, also reduced the levels of IL-4 and IL-5 in BALF and decreased inflammatory cell infiltration and mucus secretion in lung tissue. The expression of β2AR was significantly increased in the asthma group after postEA-BL13, indicating that postEA-BL13 alleviates bronchial inflammation via β2AR signaling.

Discussion

This study demonstrated that EA at the BL13 acupoint effectively alleviates airway inflammation by activating somatosensory–sympathetic pathways. EA-BL13 activates primary sensory neurons in the DRG, which transmit sensory information to SPNs in the IML nuclei, thereby activating sympathetic nerves in the lung. The activation of sympathetic nerves leads to the release of catecholamines, which activate β2AR on T cells, reducing the levels of IL-4 and IL-5 through the cAMP/PKA signaling pathway.

The findings provide a new explanation and clinical basis for the use of EA-BL13 in treating allergic asthma and other respiratory disorders related to airway inflammation. EA-BL13 can be used both before and after the induction of asthma symptoms, making it a versatile treatment option.

Conclusion

This study elucidated the neuroanatomical mechanisms through which EA-BL13 alleviates airway inflammation in allergic asthma. By activating somatosensory–sympathetic pathways and the β2AR-mediated cAMP/PKA signaling pathway, EA-BL13 reduces inflammatory cell infiltration, mucus secretion, and cytokine production. These findings support the use of EA-BL13 as a treatment for allergic asthma in both the attack and remission stages, as well as for other respiratory disorders.

doi.org/10.1097/CM9.0000000000003074

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