ACTION OF GLUTAMIC ACID AND OTHER NATURALLY OCCURRING AMINO-ACIDS ON SNAIL CENTRAL NEURONS,

The action of glutamic acid and other naturally occurring amino-acids in gasteropod nervous system was studied on the central neurons of the snails Cryptomphallus aspersa and Helix pomatia, using microelectrophysiological methods. Snail neurons are sensitive to glutamic acid in concentrations 5 X 10 to the minus 7th power M. This amino-acid may produce opposite effects on different cells Some neurons are depolarized and excited, while others are hyperpolarized and excited, while others are hyperpolarized and inhibited. These responses can be elicited both by perfusion and local ionophoretic injection of the drug. The hyperpolarizing effect shows an inversion potential of ca-60 mV. Glutamic acid in concentrations of 0.001M strongly diminishes the membrane resistance In more diluted solutions it may affect the spike propagation mechanism. Monocarboxylic and dicarboxilic amino-acids may or may not have the same effect on different neurons. In a great number of cells GABA has a strong depolarizing action. Glutamate receptors of snail neurons show desensitization when the action of the drug is depolarizing but they are not desensitized when the drug hyperpolarizes the neuron. The results are discussed in relation to the mechanisms of drug action and synaptic transmission in the snail nervous system. Author