Effects of exciting habenula by L-glutamic acid on the pain threshold and acupuncture analgesia

The latencies of tail-flick induced by nociceptive stimuli with radiant heat were measured as pain threshold in 52 rats. The pain threshold and acupuncture analgesic effects were observed after microinjection of L-glutamic acid (8.5-34 nmol) into habenula. It was found that the pain thresholds were decreased (p<0.01) and lasted 60 min. And the analgesic effect produced by needling “Zusanli” points which would obviously increase the pain threshold was abolished (p<0.01), even for 110 min in 3 rats. The results show that habenula, the axis from forebrain limbic system to brain stem, plays an important role in the acupuncture analgesia as well as the pain threshold in rats.