Endomorphin-1 mediates 2 Hz but not 100 Hz electroacupuncture analgesia inthe rat

This work was designed to elucidate the possible involvement of endogenous endomorphin-1 (EM1) in analgesia induced by electroacupuncture of low or hi gh frequencies. Taking radiant heat tail flick latency (TFL) as an indicati on of nociception, rats were subjected to intrathecal (i.t.) injection of 1 0 mu l antiserum against EM1 (EM1-AS) or normal rabbit serum (NRS, as contr ol) and then followed by 2 or 100 Hz electroacupuncture stimulation for 30 min. The analgesia induced by 2 Hz electroacupuncture was attenuated by i.t . injection of EM1-AS at 1:10 and 1:100 but not at 1:1000 dilution. No such suppressive effect was observed for 100 Hz EA analgesia when EM1-AS was in jected i.t. at any dilutions. These results indicate that EM1 is involved i n 2 Hz but not 100 Hz electroacupuncture analgesia at spinal level. (C) 199 9 Elsevier Science Ireland Ltd. All rights reserved.