[The effect of excitatory amino acid antagonists on postsynaptic potentials in the motoneurons of the frog Rana ridibunda].

The effects of excitatory amino acids on postsynaptic potentials (PSP) generated by activation of three synaptic inputs in isolated frog Rana ridibunda spinal cord motoneurons were investigated. PSP evoked by dorsal root (DR) and reticular formation (RF) stimulation were blocked by kynurenate (0.5-1 mM) and CNQX (1 mkM). However, the resistivity of RF PSP and DR PSP to kynurenate and CNQX was recorded in 7 and 4 cases respectively. APV blocked the late phase of DR and RF PSP, but did not decrease the amplitude of the early phase. Lateral column (LC) PSP generated in the same cell by LC stimulation was not decreased by kynurenate or CNQX at all. LC PSP was blocked by APV in 1 of 6 cells and it was blocked by the mixture of strychnine and APV in 2 of 6 cells. DR and RF PSP resistant to kynurenate were also blocked by the mixture of strychnine, picrotoxin and APV in 3 of 17 cells. Strychnine itself did not block LC PSP or resistant DR and RF PSP. Moreover, LC PSP was depressed, whereas RF and DR PSP were potentiated while glutamate was added into superfusing solution.