To explore the role and mechanism of mechanically sensitive ion channel Piezo2 in mechanical allodynia of rats with low back pain induced by simulating the low-frequency vibration of a helicopter.

Low-frequency vibration (LFV) model with 3-dimensional 6 degrees of freedom was used to induce low back pain in awake rats in a sitting position. Twenty-four male SD rats (8 weeks old) were randomly divided into control (Ctrl) group and LFV group. HE staining was used to evaluate the injury of the multifidus muscle. Von Frey test was carried out to detect pain sensitivity. Open field test was employed to assess the spontaneous activity and anxiety. ELISA, Western blotting and immunofluorescence staining were performed to detect the expression of NGF, TrkA and downstream molecule Piezo2. Dorsal root ganglia (DRG) neurons was isolated from SD rats and primarily cultured. After identified with immunofluorescence staining, the neurons were divided into the Ctrl group, the LFV group, and the LFV+ D-GsMTx4 (D-G4, an Piezo2 channel antagonist) group. Western blotting was used to detect the protein expression of Piezo2, and a calcium ion fluorescent probe was utilized to detect the intracellular Ca²⁺. The DRG neurons were pretreated with 50 ng/mL NGF for 1 h. Calcium ion fluorescent probe was used to observe the changes in intracellular Ca²⁺ in the LFV group, the LFV+NGF group, and the LFV+NGF+D-G4 group.

The rats of the LFV group showed abnormal morphology in multifidus muscles, accompanied with inflammatory cell infiltration, decreased paw withdrawal reflex threshold (P<0.05), and shortened total active time and active time in the centre, and decreased distance traveled in the centre (P<0.05), while prolonged total stationary time, stationary time in the periphery, and increased distance traveled in the periphery (P<0.05), and moreover, enhanced expression of Piezo2, NGF and TrkA in the DRG tissues (P<0.05). Cell experiments showed that compared with the Ctrl group, the expression of Piezo2 in the neurons was increased (P<0.05), and the intracellular Ca²⁺ level was significantly elevated in the LFV group (P<0.05). Compared with the LFV group, the Ca²⁺ level was higher in the LFV+NGF group (P<0.05), and the sensitization effect of NGF on Piezo2 was reversed after D-G4 treatment (P<0.05).

Sustained low-frequency vibration induces low back pain and mechanical allodynia in rats through the NGF-TrkA/Piezo2 pathway.

To establish an acute low back pain (ALBP) model by simulating low-frequency vibration of helicopters and explore the causes of ALBP in army aviation pilots in order to provide a reliable animal model and evaluation method for its pathogenesis and protection.

Forty-eight male SD rats (8 weeks old, weighing 200±20 g) were selected and randomly divided into groups A, B and C, with vibration for 1, 3 and 6 h, respectively, and group D as blank control, with 12 rats in each group. The rats were fixed in sitting posture on a vibrating table (10 Hz, with 6 degree vibration) for corresponding durations during 5 consecutive days. Animal behavioral tests were performed before and on days 1, 4, 7 and 14 after modelling, including paw withdrawal threshold, open field test, rotarod fatigue test, gait analysis, and 24-hour food intake assessment. Finally, light microscopy was used to observe the morphological structure of the multifidus muscle.

Behavioral examinations revealed that persistent low-frequency vibration resulted in decreased foot-contraction reflex thresholds (P < 0.01), amount of 24-hour food consumption (P < 0.01), count of upright standing (P < 0.05), rotarod velocity at rat falling off (P < 0.05), duty cycle (P < 0.05), footprint surface area (P < 0.05), and walking speed (P < 0.05). Histological observation for the multifidus muscle demonstrated cellular edema and myocyte disorganization accompanied by inflammatory cell infiltration and aggregation.

Continuous exposure to a low-frequency vibration leads to significant low back pain-related behaviors and histological changes in the lumbar multifidus muscle of rats.