AMONG the amino-acids present in vertebrate nervous systems which mimic, and are thereby candidates as, neural transmitters of inhibition, γ-aminobutyric acid (GABA) is important because it occurs almost uniquely in the central nervous system. Recently, glycine was promoted as a more likely alternative to GABA because of its apparent association with interneurones in the cat spinal cord1. Inhibition in the vertebrate nervous system can conveniently be classified on the basis of whether or not it is blocked by strychnine. The candidature of glycine as an inhibitory transmitter at the cat motoneurone was enormously advanced when it was found that its effects, like the physiological inhibition, could be prevented by strychnine2. GABA, which seemed unaffected, could presumably qualify as an inhibitory transmitter only in strychnine-insensitive pathways3.
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