Evidences obtained from different lines have shown that 5-hydroxytry- ptamine (5-HT) plays an important role in mediating electroacpuncture ana- lgesia (EAA). However

Cheng and Pomeranz in 1979 reported that p-chlo- rophenylalanine(pCPA)

the specific inhibitor of the 5-HT synthetic enzy me

was effective in decreasing only high frequency EAA

but not the low frequency EAA in the mice. To evaluate whether this is true in the rat

we have used EA of 4 frequencies (2

15

100Hz fixed frequency and 2-15 Hz changing frequenecy EA stimulations) and 2 intensities (3V

9V) to assess the effect of pCPA on EAA. The effect of EAA in control rats injected with normal saline were rather stable in a period of 2 weeks. Intraperitoneal injection of pCPA 320mg/kg) resulted in a marked decrease (-84% to-90%) of the effect of EAA 3 and 5 days after the ip injection

followed by a gradual recovery which completed in 13 days. The decrease of EAA was of similar degree whether low or high frequency

weak or strong intensity EA stimulations were used. It is thus concluded that 5-HT is important in mediating not only high frequency

but also low frequency EA analgesia in the rat.