Objective To observe the effect of different frequency electroacupuncture(EA) on hippocampal substance P(SP) andβ-endorphin(β-EP) in rats with gastralgia so as to explore its underlying mechanism in preventing and relieving visceral pain.Method Fifty rats were randomly divided into control

sham operation

model

low- frequency-EA and high frequency -EA groups.Gastralgia model was duplicated by gastric distension(a pressure of 40 mmHg) with a latex balloon.Low(2 Hz) and high(100 Hz) frequency EA was applied to bilateral"Zusanii(ST 36)"for 30 min.Pain score was given by using Al-Chaer's method(abdominal withdrawal reflex) and the expression of hypothalamicβ-EP and SP was detected by immunohistochemistry. Results Both low- and high-frequency EA of ST 36 could significantly lower the pain score(P<0.01).and the effect of high-frequency EA was markedly superior to that of low-frequency(P<0.01).Compared with control and sham-operation groups

both SP immuno-reaction(IR) andβ-EP IR positive cells in the hypothalamus in model group increased significantly in the number (P<0.01).suggesting an upregulation of SP andβ-EP expression after occurrence of gastralgia.In comparison with model group

the number of SP IR andβ-EP IR positive cells in the hypothalamus in low frequency and high frequency EA groups increased further(P<0.01) particularly in low frequency EA group.Conclusion Both low-frequency and high-frequency EA of"Zusanli(ST 36)"can effectively relieve gastric distension-induced gastralgia in the rat

and the effect of high-frequency EA is better

which may be closely related to its actions in promoting the release and synthesis of hypothalamicβ-EP and SP.