摘要：

Excitatory amino acids are employed as neurotransmitters in the majority of excitatory synapses in the brain (Watkins and Evans, 1981). At present, four subtypes of receptor are recognized, and defined on the basis of their preferred agonists as being N -methyl-D-aspartate (NMDA), quisqualate (Quis), kainate (K) or metabolotropic receptors. Of these, only the NMDA receptor is at all well characterized, largely as a consequence of the availability of specific antagonists acting at a number of apparently different sites on the receptor complex. This receptor gates a channel in neuronal membranes which is permeable to sodium and to calcium. The classical antagonists for NMDA receptors are 2-amino-5-phosphono-alkane carbonic acid derivatives such as 2-amino-5-phosphonopentanoic acid (AP5), which compete with excitatory amino acids for their binding sites at this receptor (e.g. Foster and Fagg, 1984). Additionally, however, a number of well-known pharmacological agents act as non-competitive antagonists, acting at a site apparently within the ion channel; among these are the dissociative anaesthetics such as ketamine (Honey et al ., 1985), the hallucinogenic phencyclidine (Anis et al ., 1983) and the experimental anticonvulsant, MK 801 (Wong et al ., 1986).

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