Actions of glutamate, kainate, dihydrokainate and analogues on leech neurone acidic amino acid receptors.

Intracellular recordings have been made from leech Retzius cells. L-Glutamate and kainate both excite these cells, kainate being about 100 times more potent than glutamate. Cross desensitization was observed between glutamate and kainate. Dihydrokainate was found to be equipotent with kainate on these neurones. Esterification of either kainate or dihydrokainate rendered the compounds inactive as did the addition of a benzyloxycarbonyl group on the nitrogen of both compounds. These results suggest that the double bond in the side chain of kainate is not necessary for its potent activity on leech Retzius neurones. But, that free carboxyl groups and an unsubstituted nitrogen are essential for glutamate-like activity.