The experiments were carried out on rats

anesthetized with urethan and paralyed with tubocuraine. Stainless steel needles were inserted into bilateral "Zusanli" points. The unit discharges of RVM neurons were recorded extracellalarly by microelectrode. The searching of nociceptive neurons and processing of data were operated automatically by a real time control system. The results were as follow:1. The pain response of excitatory neurons could be inhibited by 2Hz EA (n = 15/22

P< 0.01)

the mean inhibition rate was 32. 40%.2. The inhibitory effects of 2Hz were completely blocked by naloxone pretreated (n = 5/5

P< 0.01).3. The pain response of excitatory neurons could be inhibited by 10Hz EA(n = 10/ 13

P<0. 01)

the mean inhibition rate was 49. 06%.4. The inhibitory effects of 10Hz EA were partially blocked by naloxone pretreated (n = 5/5

P<0.01).5. Both 2Hz and 10Hz EA could enhance the spontaneous discharges of excitatory neurons in RVM

and the percentage of change in the frequency was 62. 45% and 112. 02 % respectively.6. Neither 2Hz nor 10Hz EA could obviously influence the spontaneous activity of inhibitory neurons in RVM.The results suggest that both 2Hz and 10Hz EA could activate excitatory neurons in RVM

which may suppress nociceptive transmission via opioid mechanism