Objective:To observe the effect of changes of hypothalamic β EP level and expression of pro opiomelanocortin (POMC)mRNA on aftereffects of acupuncture analgesia.Methods:132 SD rats were evenly randomized into control group

model group and acupuncture group

and each group was then divided into 0 min

15 min

30 min

1 hr

2 hr

4 hr

8 hr

12 hr

18 hr and 24 hr subgroups

with 8 cases in each of the former 4 subgroups and 2 cases in each of the latter 6 subgroups. Rat inflammatory pain model (acute adjuvant arthritis) was made by injecting Freund's complete adjuvant (0.1 mL) into the right hindpaw. Right“Kunlun"(BL 60) was punctured with a filiform needle and retained for 30 min

when

the needle was manipulated once again every 5 min. Then

the pain threshold (latency of hindpaw withdrawal in responding to radiation heat stimulation) of the right hindpaw was determined with a radiation heat pain detector. Hypothalamus tissues of some rats of the abovementioned 10 subgroups were isolated to be cut into sections (6～8 μm) that were stained with in situ hybridization technique for displaying expression of POMC mRNA

and β EP content of hypothalamus tissue was determined with radioimmunoassay. Results:The pain threshold values of model group at 0 min

15 min

30 min and 1 hr were significantly lower than those of control group ( P < 0.01 )

and those of acupuncture group were all considerably higher than those of model group ( P < 0.01 ) despite being still markedly lower than those of control group at 0 min and 1 hr ( P< 0.05

0.01 ). Comparison among the 3 groups showed that β EP contents of model group and acupuncture group at 0 min

15 min

30 min and 1 hr were significantly higher than those of control group ( P < 0.05

0.01 ); and those of acupuncture group were even markedly higher than those of model group at 0 min

15 min and 1 hr ( P < 0.05

0.01 ). Changes of POMC mRNA expression in these 3 groups presented a similar tendency to those of β EP contents. Conclusion: Acupuncture has immediate effect and remarkable aftereffect in relieving pain

which may be closely related to acupuncture induced increase of β EP content and up regulation of POMC mRNA expression in the hypothalamus.