Objective:To explore the effect of scalp electroacupuncture (EA) on central pain sensitization in rats with knee osteoarthritis (KOA).Methods:Thirty-two 8-week-old female Sprague-Dawley rats were randomly divided into a blank control group, a model group, an electroacupuncture (EA) group and a sham EA group, each of 8. All of the rats except those in the control group had KOA induced through intra-articular monosodium iodoacetate injections in the right knee. Two weeks later the EA group rats began receiving daily head EA sessions 6 days/week for 2 weeks. The sham EA group received identical but non-therapeutic stimulation. The blank control and model groups received no EA intervention. Before the modelling and 3, 7, 14, 21 and 28 days later, all of the rats completed bipedal balance pain tests and mechanical allodynia evaluations. After the testing on day 28, all of the rats were euthanized for molecular analyses. Western blotting and immunohistochemistry were performed to examine protein expression of brain-derived neurotrophic factor (BDNF), tropomyosin receptor kinase B (TrkB), and cannabinoid receptor type 1 (CB1R) in both the periaqueductal gray (PAG) matter and spinal dorsal horns (SDHs). Serum levels of substance P (SP) and 5-hydroxytryptamine (5-HT) were also quantified using enzyme-linked immunosorbent assays.Results:Three days after successful modeling, the average weight-bearing capacity of the right hind limb in the model, sham EA and EA groups was significantly lower than that of the blank controls. It reached its lowest level on the 14th day after modeling. Concurrently, the pain responses in those three groups were significantly higher than among the controls, also peaking on the 14th day after modeling. After two weeks of electroacupuncture, the electroacupuncture group showed significant improvement in both right hind limb weight-bearing capacity and pain response compared to the model group. Meanwhile, the levels of BDNF and TrkB protein in the periaqueductal gray matter were significantly higher in the model group than among the blank controls, while the electroacupuncture group exhibited significantly reduced expression of BDNF and TrkB proteins compared to the model group, along with significantly increased CB1R protein expression. The model group showed significantly elevated expression of both BDNF and TrkB proteins in the spinal dorsal horn compared to the blank control group, while there were significant differences between the EA and model groups in the expression of BDNF, TrkB and CB1R proteins. Immunohistochemical analysis on day 28 revealed that the EA group had significantly fewer BDNF- and TrkB-positive cells in the PAG compared to the model group, with significantly more CB1R-positive cells. In the SDH, the model group exhibited significantly increased numbers of BDNF- and TrkB-positive cells compared to the blank control group, whereas significant differences were found between the EA and blank control groups in the numbers of BDNF-, TrkB- and CB1R-positive cells. Serum analysis on day 28 demonstrated that substance P and 5-hydroxytryptamine levels in the model, sham EA and EA groups were significantly higher than in the blank control group, on average. However, no significant differences were observed in serum SP and 5-HT levels between the EA and model groups.Conclusions:Scalp EA significantly alleviates central pain sensitization in KOA, at least in rats, potentially by suppressing BDNF and TrkB expression while upregulating CB1R expression in the PAG matter and the SDH.

Objective:To explore the effect of scalp electroacupuncture (EA) on central pain sensitization in rats with knee osteoarthritis (KOA).Methods:Thirty-two 8-week-old female Sprague-Dawley rats were randomly divided into a blank control group, a model group, an electroacupuncture (EA) group and a sham EA group, each of 8. All of the rats except those in the control group had KOA induced through intra-articular monosodium iodoacetate injections in the right knee. Two weeks later the EA group rats began receiving daily head EA sessions 6 days/week for 2 weeks. The sham EA group received identical but non-therapeutic stimulation. The blank control and model groups received no EA intervention. Before the modelling and 3, 7, 14, 21 and 28 days later, all of the rats completed bipedal balance pain tests and mechanical allodynia evaluations. After the testing on day 28, all of the rats were euthanized for molecular analyses. Western blotting and immunohistochemistry were performed to examine protein expression of brain-derived neurotrophic factor (BDNF), tropomyosin receptor kinase B (TrkB), and cannabinoid receptor type 1 (CB1R) in both the periaqueductal gray (PAG) matter and spinal dorsal horns (SDHs). Serum levels of substance P (SP) and 5-hydroxytryptamine (5-HT) were also quantified using enzyme-linked immunosorbent assays.Results:Three days after successful modeling, the average weight-bearing capacity of the right hind limb in the model, sham EA and EA groups was significantly lower than that of the blank controls. It reached its lowest level on the 14th day after modeling. Concurrently, the pain responses in those three groups were significantly higher than among the controls, also peaking on the 14th day after modeling. After two weeks of electroacupuncture, the electroacupuncture group showed significant improvement in both right hind limb weight-bearing capacity and pain response compared to the model group. Meanwhile, the levels of BDNF and TrkB protein in the periaqueductal gray matter were significantly higher in the model group than among the blank controls, while the electroacupuncture group exhibited significantly reduced expression of BDNF and TrkB proteins compared to the model group, along with significantly increased CB1R protein expression. The model group showed significantly elevated expression of both BDNF and TrkB proteins in the spinal dorsal horn compared to the blank control group, while there were significant differences between the EA and model groups in the expression of BDNF, TrkB and CB1R proteins. Immunohistochemical analysis on day 28 revealed that the EA group had significantly fewer BDNF- and TrkB-positive cells in the PAG compared to the model group, with significantly more CB1R-positive cells. In the SDH, the model group exhibited significantly increased numbers of BDNF- and TrkB-positive cells compared to the blank control group, whereas significant differences were found between the EA and blank control groups in the numbers of BDNF-, TrkB- and CB1R-positive cells. Serum analysis on day 28 demonstrated that substance P and 5-hydroxytryptamine levels in the model, sham EA and EA groups were significantly higher than in the blank control group, on average. However, no significant differences were observed in serum SP and 5-HT levels between the EA and model groups.Conclusions:Scalp EA significantly alleviates central pain sensitization in KOA, at least in rats, potentially by suppressing BDNF and TrkB expression while upregulating CB1R expression in the PAG matter and the SDH.