Objective To observe the activation effect of histamine on mast cells in the acupoint area and its analgesic effects similar to acupuncture stimulation

so as to reveal the underlying mechanism of acupoint injection therapy.Methods A total of 60 SD rats were divided into control

model

normal saline(NS)

histamine-injection and acupuncture groups(12 rats/group).Acute adjuvant-induced-arthritis(AIA) model was duplicated by injection of complete Freunds' Adjuvant(0.05 mL) into the left ankle articular cavity.For rats of saline and histamine groups

normal saline(50 μL) and histamine(50 μL

100 μg/mL) were injected into the left "Zusanli"(ST 36) acupoint area.For rats of acupuncture group

manual acupuncture(lifting-thrusting and twisting needle intermittently) was applied to ST 36 for 20 min.Paw withdrawal(pain threshold

PT) was detected by radiant heat irradiation of the hindpaw.Skin and muscle tissues of ST 36 area were sampled to be fixed in formalin

then

sliced(5 μm)

and stained with Toluidine Blue

separately

followed by counting the degranulation rate of mast cells under microscope.Results Compared with normal control group and pre-modeling

PT of model

NS

acupuncture and histamine groups decreased significantly(P<0.01)

while in comparison with model group

PT of acupuncture and histamine groups increased considerably(P<0.01)

suggesting an induction of analgesic effect after acupuncture and histamine injection.The degranulation rates of acupuncture and histamine groups were remarkably higher than those of model and NS groups(P<0.01)

suggesting an activation of mast cells following regional acupuncture stimulation and histamine injection.Conclusion Both manual acupuncture and histamine injection of ST 36 can relieve pain in AIA rats

which may be closely related to its effect in activating mast cells in acupoint area.It suggests that the mast cells are a new target for acupoint injection therapy.