The purpose of this study is to observe the effect of intracerebroventricular (iv)and intra-PAG injection of substance P (SP)on serotonin(5-HT)conte- nts of hypothalamus

hippocampus

striatum and its relation with the change of pain thre shold

electroacupuncture (EA)analgesia

The results were as follows:(1)After icy injection of SP

the pain threshold and the 5-HT co- ntents of hypothalamus

nippocampus were significantly increased

After de- pletion of the 5-HT contents in brain by pCPA

the inhibitor of 5-HT synthe- sis

the effect of SP on elevating pain threshold and the 5-HT contents of hypothalamus

hippocampus were markedly attenuated

bud did not prevent the analgesic effect of SP (2)The pain threshold and the 5-HT contents of hypo- thalamus

hippocampus were dose-dependently increased by intra-PAG injection of SP.(3)The intra-PAG injection of SP introduced simultanously with high or low frepuency EA did not affect the change of 5-HT contents of three brain regions

but caused a more marked elevation of pain threshold

These results suggest that the serotoninergic system may be activated by PAG for the medi- ation of SP induced analgesia.There is a synergic action of analgesia bet- ween the effects produced by intra-PAG injection of SP and those by high or low frepuency EA.