The present experiments were designed to study the effect of glutamate on cortical somatosensory area Ⅱ (S Ⅱ) producing descending modulation of intralaminar nuclei (ILN) via the motor cortex (MCtx) in acupuncture analgesia. The glutamate antagonist glutamate diethylester (GDEE) or saline was topically applied at MCtx in 17 cats. Single unit activities of ILN neurons were extracellularly recorded. The results were as follows:1. The nociceptive responses of ILN neurons were attenuated by stimulating S Ⅱ after topical administration of saline at MCtx. However

The inhibitory effect of stimulating S Ⅱ in the same neurons was reduced after application of GDEE. There was a significant difference at 0′ - 1′ after the stimulation between the two groups (n = 10

P<0. 05).2. The inhibitory effect of electroacupuncture (EA) on nociceptive responses was reduced after topical application of GDEE

while marked inhibition was shown at 0′- 10′ after cessation of EA in the saline control group (n=11

P<0. 05).The results

together with the finding that the majority of S Ⅱ neurons could be activated by EA

showed that glutamate released from S Ⅱ to MCtx might be involved in corticofugal modulation of ILN from S Ⅱ via MCtx in acupuncture analgesia