Do kappa opioids mimic sigma agonists as amino acid antagonists?

The kappa opioids tifluadom and U-50,488 H, when tested on spinal neurones of rats in vivo and frogs in vitro, had no selective effect on responses to microelectrophoretically or bath applied N-methyl-D-aspartate, quisqualate or kainate. In the same preparations ketamine selectively reduces responses to N-methyl-D-aspartate. Amino acid antagonism by dissociative anaesthetics and sigma opioids is thus not mediated by that binding site which kappa and sigma opioids have been reported to have in common.