Electroacupuncture Reduces Central Sensitization in NERD Rats via NGF/TrkA Pathway

Background and objectives

This study investigated whether electroacupuncture (EA) can reduce central sensitization in a rat model of non-erosive reflux disease (NERD) characterized by a liver-stomach disharmony pattern, and explored mechanisms focused on the NGF/TrkA signaling pathway in the spinal cord. Central sensitization and visceral hypersensitivity are implicated in NERD pathophysiology; the authors tested EA effects on behavioral, biochemical, molecular, and ultrastructural endpoints.

Methods

Forty male Sprague-Dawley rats were randomized into four groups (n = 10 per group): control, model, EA, and medication (Western medicine). The NERD model combined a basic sensitization protocol—intraperitoneal injection of ovalbumin plus aluminum hydroxide adjuvant—with repeated chronic tail-pinching stress. Interventions lasted two weeks.

• EA group: electroacupuncture at Zhiyang (GV9), Shendao (GV11), Dazhui (GV14), and Baihui (GV20), 30 minutes per session, once daily for two weeks. Stimulation parameters: 2 Hz frequency and intensity sufficient to induce a slight limb tremor.

• Medication group: omeprazole administered by gavage at 1.8 mg/kg once daily for two weeks.

Control and model groups received equivalent volumes of distilled water.

Behavioral and physiological assessments

Behavioral and physiological measurements were conducted before and after interventions and included:

• Sucrose preference test to assess anhedonia-like behavior.
• Mechanical withdrawal threshold (MWT) measured with von Frey filaments.
• Abdominal withdrawal reflex (AWR) scoring at graded esophageal pressures (including 40, 60, 80 mmHg) after intervention, and an esophageal acid perfusion test to assess visceral pain threshold.
• Body weight monitoring.
• Serum gastrin (GAS) and motilin (MTL) concentrations measured by ELISA.

Molecular and immunofluorescence analyses

Spinal cord tissue was analyzed for protein and mRNA markers associated with central sensitization and synaptic activity:

• Western blot quantified protein expression of nerve growth factor (NGF), tropomyosin receptor kinase A (TrkA), glutamate receptor AMPA subunit 1 (GluA1), and postsynaptic density protein 95 (PSD95).
• Real-time quantitative PCR measured NGF and TrkA mRNA levels in spinal cord tissue.
• Immunofluorescence staining assessed the positive expression and fluorescence intensity of GluA1 and PSD95 in the spinal cord.

The study focused on these markers because NGF/TrkA signaling and postsynaptic AMPA/PSD95 expression are linked to synaptic plasticity and central sensitization.

Ultrastructural examination by electron microscopy

Transmission electron microscopy (TEM) was used to observe ultrastructural changes:

• Number of synaptic vesicles in dorsal horn synapses of the spinal cord.
• Intercellular space between esophageal mucosal epithelial cells.

These ultrastructural endpoints were used to evaluate synaptic activity and mucosal barrier integrity associated with the model and interventions.

Results

Compared with control animals, model rats exhibited multiple signs consistent with central sensitization and visceral hypersensitivity:

• Behavioral and physiological: decreased sucrose preference rate, reduced MWT, lower body weight, decreased visceral pain threshold, and higher AWR scores at 40, 60, and 80 mmHg (all P < 0.01).
• Serum markers: decreased GAS and MTL contents (P < 0.01).
• Molecular and imaging: increased number of spinal synaptic vesicles and widened intercellular spaces in esophageal mucosal epithelial cells by TEM; elevated protein expression of NGF, TrkA, GluA1, and PSD95 in spinal cord tissue; increased NGF and TrkA mRNA (all P < 0.01); and higher immunofluorescence intensity for GluA1 and PSD95 (P < 0.01).

Intervention effects:

• Both EA and omeprazole groups reversed many model-induced changes: sucrose preference rate, MWT, visceral pain threshold, and serum MTL increased versus model (P < 0.01 or P < 0.05); AWR at 40 mmHg decreased (P < 0.01 or P < 0.05); spinal NGF, PSD95, and TrkA protein expressions and TrkA mRNA decreased (P < 0.01 or P < 0.05).

• EA-specific effects: compared with model, EA reduced AWR scores at 60 and 80 mmHg (P < 0.01), increased serum GAS (P < 0.01), lowered spinal NGF mRNA (P < 0.01), and reduced GluA1 and PSD95 immunofluorescence intensity (P < 0.01). EA decreased the number of spinal synaptic vesicles and promoted recovery of esophageal epithelial intercellular spacing as seen on TEM.

• Comparative effect: EA was superior to omeprazole in raising MWT and visceral pain threshold (P < 0.01). The medication group still showed improvements versus model but had lower visceral pain threshold and MWT than the EA group (P < 0.01).

Discussion and conclusions

The authors conclude that electroacupuncture alleviated visceral hypersensitivity and reduced central sensitization in this rat model of NERD with liver-stomach disharmony. The therapeutic effects correlated with downregulation of spinal cord NGF/TrkA signaling, reductions in synaptic markers (GluA1, PSD95), decreased synaptic vesicle number on TEM, and partial restoration of esophageal epithelial intercellular structure. EA demonstrated advantages over omeprazole on certain nociceptive endpoints (MWT and visceral pain threshold) in this experimental setting.

These findings support a potential mechanism whereby EA modulates spinal NGF/TrkA signaling and synaptic plasticity to reduce central sensitization and visceral pain responses in this preclinical NERD model.

Conflict of interest and reporting limitations

All authors declared no conflict of interest. The abstract reports key experimental design, interventions, endpoints, and group-level statistical directions and significance levels, but detailed numerical data, full methods (for example, exact timing of assessments relative to interventions), and raw data were not provided in the source abstract. Readers should consult the full text for comprehensive methodological and data details.