Comparative actions of glutamate and related substances on the lateral line of xenopus laevis.

The effects of compounds structurally related to L-glutamate were compared on spontaneous activity of afferent nerve fibres in Xenopus laevis lateral-line. The potencies (EPMR) of several compounds relative to L-glutamate (EPMR = 1) were: L-aspartate (EPMR = 1), D-aspartate (EPMR = 1), D-glutamate (EPMR = 1.98), quisqualate (EPMR = 0.0015), kainate (EPMR = 0.0045), dihydrokainate (EPMR = 0), ibotenate (EPMR = 1.5), L-homocysteate (EPMR = 0.17), 2,4,5-trihydroxyphenylalanine (6-OH-DOPA, EPMR = 0.23), and D-homocysteate (EPMR = 0.73), N-methyl-D,L-aspartate (EPMR = 5), and N-methyl-D-aspartate (NMDA, EPMR = 1). Several compounds, including gamma-aminobutyrate (GABA), suppressed spontaneous activity without eliciting excitatory responses. The results reveal receptors that are present at this vertebrate peripheral synapse.