Effects of excitatory amino acid antagonists on synaptic transmission in the ampullae of Lorenzini of the skate Raja clavata

Abstract

1. The effects of excitatory amino acid antagonists on synaptic transmission in the ampullae of Lorenzini of the skate Raja clavata were studied. 2. At concentrations of 10(-3) to 10(-6) M. L-glutamic acid diethylester (GDEE) and L-glutamic acid dimethylester (GDME) decreased the resting afferent discharge frequency as well as the electrically evoked activities and depressed the responses to application of excitatory amino acids. 3. D-alpha-Aminoadipic acid (AA) and 2-amino-4 phosphonobutyric acid (APB) had practically no effect either on resting afferent discharge or on evoked afferent activity. 4. 2-Amino-5-phosphonovaleric acid (APV) reduced the resting afferent discharge and electrically evoked activity in the afferent fibres. APV blocked N-methyl-D-aspartate (NMDA) induced responses at a lower concentration than those induced by aspartate,. 5. Responses caused by NMDA were Mg 1(2+)-dependent; those to quisqualate (Q) application depended to a lesser degree on the Mg2+ concentration. 6. Cis-2,-3-piperidinedicarboxylic acid (PDA) blocked both the resting afferent discharge and the electrically evoked activity; it also reversibly blocked the postsynaptic, amino acid-induced responses. The L-glutamate (L-GLU) response was more resistant to the blockade than the L-aspartate (L-ASP) response. 7. Both kynurenic acid (KEN) and gamma-D-glutamylglycine (DGG) reduced the resting and evoked activities in the afferent fibres. L-ASP was more resistant to blockade by KEN than L-GLU. 8. These observations suggest a prominent physiological role of quisqualate-, kainate- and NMDA-preferring receptors in the ampullae of Lorenzini of Raja clavata.