The use of the procaine-blocked hemisected spinal cord preparation to identify the primary action of amino acids and their antagonists on amphibian mononeurones is described. 2 Apart from an anomalous effect of glycine, the responses of frog spinal motoneurones to amino acids were shown to be similar to those of mammalian spinal neurones. 3 In the presence of procaine, gamma-aminobutyrate (GABA), taurine and beta-alanine caused a hyperpolarizing response, measured in ventral roots, whereas L-glutamate and, to a lesser extent, glycine caused depolarization. 4 Picrotoxin and bicuculline specifically blocked ventral root responses to GABA; strychnine blocked responses to taurine and beta-alanine but not responses to L-glutamate, glycine or GABA.
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