Amino acid receptors
There are two amino acid neurotransmitters, namely GABA and glutamate, which have been of major interest to the psychopharmacologist because of the potential therapeutic importance of their agonists and antagonists. The receptors upon which GABA and glutamate act to produce their effects differ from the ‘‘classic’’ transmitter receptors in that they seem to exist as receptor complexes that contain sites for agonists, in addition to the amino acid transmitters; these sites, when occupied, modulate the responsiveness of the receptor to the amino acid. For example, the benzodiazepines have long been known to facilitate inhibitory transmission, and their therapeutic properties as anxiolytics and anticonvulsants are attributable to such an action. It is now apparent that benzodiazepines occupy a receptor site on the GABA receptor complex which enhances the responsiveness of the GABA receptor to the inhibitory action of GABA. Similarly, it has recently been shown that the inhibitory transmitter glycine can act on a strychnineinsensitive site on the N-methyl-D-aspartate (NMDA) receptor, and thereby modify its responsiveness to glutamate.Knowledge of the mechanisms whereby the amino acid transmitters produce their effects has been valuable in the development of psychotropic drugs that may improve memory, reduce anxiety, or even counteract the effects of post-stroke hypoxia on brain cell survival. Some of these aspects are considered later.
There are two amino acid neurotransmitters, namely GABA and glutamate, which have been of major interest to the psychopharmacologist because of the potential therapeutic importance of their agonists and antagonists. The receptors upon which GABA and glutamate act to produce their effects differ from the ‘‘classic’’ transmitter receptors in that they seem to exist as receptor complexes that contain sites for agonists, in addition to the amino acid transmitters; these sites, when occupied, modulate the responsiveness of the receptor to the amino acid. For example, the benzodiazepines have long been known to facilitate inhibitory transmission, and their therapeutic properties as anxiolytics and anticonvulsants are attributable to such an action. It is now apparent that benzodiazepines occupy a receptor site on the GABA receptor complex which enhances the responsiveness of the GABA receptor to the inhibitory action of GABA. Similarly, it has recently been shown that the inhibitory transmitter glycine can act on a strychnineinsensitive site on the N-methyl-D-aspartate (NMDA) receptor, and thereby modify its responsiveness to glutamate.Knowledge of the mechanisms whereby the amino acid transmitters produce their effects has been valuable in the development of psychotropic drugs that may improve memory, reduce anxiety, or even counteract the effects of post-stroke hypoxia on brain cell survival. Some of these aspects are considered later.
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