<正> Radioimmunoassay was employed to dctermine the immunorcactivc met-enkephalin（ir-MEK）contents of several brain regions .The pain threshold（PT）andir-MEK content of striatum and hypothalamus increased markedly afterintraoerebroventricular injection of substance P（SP）in the dosage of lμgg/10μl

but nosignificant change of ir-MEK content in hippocampus was observed.When theperiaqueductal gray（PAG）was destroyed with electrolysis

the increase of PT andir-MEK content in the two brain regions after SP injection was obviouslysuppressed（P<0.05-0.01）.The PT and ir-MEK content of hypothalamus andstriatum would also increase after intra-PAG injection of SP（0.4μg/4μl）

electroacupuncture or intraperitoneal injection of morphine.The ir-MEK content ofhippocampus could also increase after intra-PAG injection of SP or intraperitoncal injec-tion of morphine.The combination of intra-PAG injection of SP andelectroacupuncture caused a more marked elevation of PT and ir-MEK content of the 3brain regions than either of the two used singly could（P<0.01 ）.The combined effect ofintra-PAG injection of SP and intraperitoneal injection of morphine was similar to thatof either of the two used singly（P>0.05）.These facts indicate that thc analgesic effect ofSP activated by PAG was mediated through the increase of cerebral met-cnkcphalin con-tent

and there was a synergic effect between SP and elcctroacupuncturc.