[Intracellular analysis of the effects of micro-application of several amino acids on lumbar motor neurons of Rana ridibunda frogs]

Abstract

Intracellular recordings were made from lumbar motoneurones of the isolated spinal cord of the frog while glutamate, GABA or glycine were applied iontophoretically through the extracellular microelectrode. Glutamate had depolarizing excitatory effects and caused slight (if any) increase in membrane conductance. Responses to BABA and glycine were inhibitory regardless of the sign of membrane potential shift as revealed by conductance measurements and the dependence of anti- and orthodromically induced potentials on their application. Blocade of synaptic transmission by reducing extracellular Ca++ and increasing Mg++ concentrations did not alter the effects of application indicating the immediate activation of the postsynaptic membrane. These results are in agreement with the possible role of GABA and glycine as transmitters in inhibitory as transmitters in inhibitory synapses. The function of glutamate remains uncertain.