Objective To study the mechanism of analgesic effect of Xiongzhi Dilong Decoction [Decoction of Chuanxiong （Rhizoma Ligustici Chuangxiong）

Baizhi （Radix Angelicae Dahuricae）

Dilong （Lumbricus）] on the migraine model rats. Methods The 48 healthy male SD rats were randomized into 4 groups:normal saline group

model group

Sumatriptan group

and Chinese medicine group

with 12 in each. The migraine models were made by subcutanous injection of nitroglycerin

and the brain tissue samples were collected 4h and 6h after medication intervention. The immunohistochemical staining technique was then conducted to determine the expression of celluar oncogene fos （c-fos） and 5-hydroxytryptamine （5-HT） in SPN 5 and PAG. Results Expression in SPN 5:A reduction of c-fos expression in the Chinese medicine group was observed

with a decrease in expression from 4h to 6h. There was statistical difference in comparing with that of the model group （P<0.01）. An increase of 5-HT expression in the Chinese medicine group was noticed

with a slight decrease in expression from 4h to 6h. There was statistical difference in comparing with that of the model group （P<0.05

P<0.01）. Expression in PAG:c-fos expression in the Chinese medicine group was reduced

with decrease in expression from 4h to 6h. There was statistical difference in comparing with that of the model group （P<0.01）. The increase of 5-HT expression in the Chinese medicine group was more significant

and the positive cell was more at 6h than at 4h. There was statistical difference in comparing with that of the model group （P<0.01）. Conclusion Xiongzhi Dilong Decoction is able to reduce the c-fos expression induced by nitroglycerin

increase the 5-HT expression

hence depressing excitability in neurons of SPN 5 by stimulating the descending 5-HT analgesic pathway. This effect can last for a long period of time

to make the pain threshold increased and the transmission of nociceptive information inhibited.