1 Animal experiment
1.1 Rearing rats
Thirty healthy 8-week-old male rats were selected (Beijing Weitong Lihua Technology Co., Ltd.) weighing 200–250 g and raised in the Laboratory of Animal Center of China Medical University. The feeding conditions were as follows: temperature (22 ± 2) ℃, relative humidity 40% -60%,12/12 h day and night alternating light, water and food ingested freely. The rats were acclimated in this environment for 3–5 days before the experiment. The experimental operation and animal feeding were in compliance with the basic regulations for animal experiments and animal ethics (2018067).
1.2 Establishment a myofascial orofacial pain model
Twelve rats were randomly divided into the masseter tendon ligation group and the sham group, with 6 rats in each group. The masseter tendon ligation group and the sham group were anesthetized with 2% pentobarbital sodium (50 mg/kg, intraperitoneal injection). Then the rats were fixed on the operating table to keep a head-up posture. In the masseter tendon ligation group, a 3 mm long anterior-posterior incision was made along the mucogingival junction of the first molar on the left side of the rats. TASM was separated carefully and gently. TASM was ligated by two chrome bowels (4.0), and the distance between them was 2 mm. Finally, the wound was sutured in layers, and apply an appropriate amount of antibiotics (gentamicin) to the wound. Rats in the sham group received the same operation except for ligation of TASM.
1.3 Behavioral testing
The rats of the masseter tendon ligation group and the sham group were placed in a quiet environment to keep the rats in a stable state. These rats were tested for mechanical pain threshold before operation and on the 4th,7th,10th and 14th days after operation. The von Frey filaments were applied vertically to the left masseter muscle area of the rats, and the mechanical pain threshold was tested. The positive reaction was to recede the body or dodge the head, scratch the face asymmetrically or bite the von Frey filaments. The von Frey filaments stimulation intensity started from 3.22 g, and when a positive reaction was caused, the von Frey filament of the adjacent lighter level was replaced. When a negative reaction was caused, the von Frey filament of the adjacent stronger level was replaced. The interval between each stimulation is 10 seconds, and the stimulation was repeated five times in total. The measurement was continued until the first negative and positive cross-reaction occurred. First the response frequencies to a series of von Frey filament forces [( number of responses/number of stimuli) *100%] were calculated, and then the stimulus-response frequency curve (S-R curve) was drawed. After a non-linear regression analysis, the EF50 value was obtained according to the S-R curve, which was defined as the effective von Frey filament force (g) that produced 50% of the response frequency. A decrease in EF50 indicated the presence of mechanical allodynia. The mechanical stimulus response threshold(EF50)was calculated by Up-Down Calculators.
1.4 Quantitative Real-time polymerase chain reaction(qRT-PCR)
On the 14th day after operation, the rats of the masseter tendon ligation group and the sham group were anesthetized with 2% sodium pentobarbital (100 mg/kg), and the rats in both groups were sacrificed by decapitation. The head of the rat was fixed on a wooden board, the skull and brain tissue of the rat were exposed. The left trigeminal ganglion, trigeminal spinal subnucleus caudalis and C1-C2 spinal cervical dorsal horn (Vc /C2) were obtained. The total RNA was extracted in trigeminal ganglion and Vc/C2 tissue according to the instructions of Trizol reagent, and determine the concentration and purity of total RNA. cDNA was formed by reverse transcription using TaKaRa's reverse transcription kit. The target cDNA was amplified using TaKaRa PCR kit. The PCR amplification conditions were: pre-denaturation at 95 ℃ for 30 s, 95 ℃ for 5 s, 61.4 ℃ for 30 s, 72 ℃ for 30 s, a total of 40 cycles, and 72 ℃ for 3 min.
The primer sequence was as follows:
Cavα2δ-1-forward:5’-TGAGTTGTTTCCAGCACCTG-3’;
Cavα2δ-1-reverse:5’-CTCTTCTCCTCCATCCGTGA-3’;
GAPDH-forward:5’-ACCACAGTC-CATGCCATCAC-3’;
GAPDH-reverse: 5’-TCCACCACCCT-GTTGCTGTA-3’;
Calculate the relative expression of the target gene using the 2−ΔΔCt method. The mRNA expression levels of Cavα2δ-1 were compared in the masseter tendon ligation group and the sham group.
1.5 Antisense oligodeoxynucleotide treatment
Eighteen male rats were randomly divided into Cavα2δ-1 antisense oligonucleotides group, Cavα2δ-1 mismatched oligonucleotides group and normal saline control group, each with 6 rats. The antisense and mismatch oligonucleotides of Cavα2δ-1 were synthesized, which had 3 nucleotide phosphorothioate modifications at the 5’and 3’ ends respectively, which were purified by a high-purity salt-free method. Cavα2δ-1 antisense and mismatch oligonucleotides had 3 nucleotide phosphorothioate modifications at the 5’ and 3’ ends, respectively, and were purified with High Purity Salt Free method. The antisense oligonucleotide sequence of Cavα2δ-1 was AGCCATCTTCGCGATCGAAG, and the mismatch oligonucleotide sequence was CGATACCTCGCTGGCTAAAG. These sequences were dissolved in sterile saline. On the 4th day after the anterior superficial tendon of the left masseter muscle was ligated, the rats that injected Cavα2δ-1 antisense oligonucleotides into the left masseter muscle were defined as the Cavα2δ-1 antisense oligonucleotides group, 10 ul each time, twice a day for 4 days. The rats that injected Cavα2δ-1 mismatched oligonucleotides into the left masseter muscle were defined as the Cavα2δ-1 mismatched oligonucleotides group, 10 ul each time, twice a day for 4 days. The rats that injected normal saline into the left masseter muscle were defined as the normal saline control group,10 ul each time, twice a day for 4 days. The mechanical pain threshold of three groups was measured before operation, the 4th, 7th, 10th and 14th day after operation.
2 Cell experiment
2.1 Cell culture
PC12 cells at passage 5 were placed in a DMEM high-glucose medium system containing 10% fetal bovine serum,100 U/mL penicillin and 100 ug/mL streptomycin, and cultured in a CO2 constant temperature incubator with a volume fraction of 5% at 37 ℃.After the cells grew to the logarithmic phase, the cell was digested to obtain a cell suspension, and the cell density was adjusted to 2 * 104 cells/ml to inoculate a 6-well plate.
2.2 Lipopolysaccharides (LPS) treatment of PC12 cells
The control group: PC12 cells was cultured with the above-mentioned medium for 36 hours.
The LPS treatment group: 24 hours after PC12 cells were cultured with the above-mentioned medium, PC12 cells were treated with 5 ug/ml LPS for 12 h.
2.3 Quantitative Real-time polymerase chain reaction(qRT-PCR)
The total RNA in the control group and the LPS treatment group was extracted according to the instructions of Trizol reagent, and the concentration and purity of total RNA were determined. cDNA was formed by reverse transcription using TaKaRa's reverse transcription kit. The target cDNA was amplified using TaKaRa PCR kit. The PCR amplification conditions were: pre-denaturation at 95 ℃ for 30 s, 95 ℃ for 5 s, 61.4 ℃ for 30 s, 72 ℃ for 30 s, a total of 40 cycles, and 72 ℃ for 3 min.
The primer sequence was as follows:
Cavα2δ-1-forward:5’-TGAGTTGTTTCCAGCACCTG-3’;
Cavα2δ-1-reverse:5’-CTCTTCTCCTCCATCCGTGA-3’;
GAPDH-forward:5’-ACCACAGTC-CATGCCATCAC-3’;
GAPDH-reverse: 5’-TCCACCACCCT-GTTGCTGTA-3’;
Calculate the relative expression of the target gene using the 2−ΔΔCt method. The mRNA expression levels of Cavα2δ-1 were compared in the control group and the LPS treatment group.
3 Statistical analysis
The data was analyzed by Sigmaplot 14, SPSS 16.0 and Graphpad prism 5. The mechanical stimulus response threshold(EF50)was analyzed by a two-way repeated analysis of variance (ANOVA). Cavα2δ-1 mRNA levels were analyzed by two independent samples t test. P < 0.05 indicated that the difference was statistically significant.