[Inhibitory regulation of glutamate receptors in the frog motoneuron]

The interaction of exogenously applied excitatory (glutamate and their agonists NMDA, AMPA, kainate) and inhibitory (glycine and GABA) amino acid effects was studied intracellularly in the motoneurones of the isolated frog spinal cord. During simultaneous glycine or GABA bath applications GLU-, AMPA-, KA- and NMDA-evoked responses were, respectively, decreased up to 45.8 +/- 2.9% (n = 12) and 67.8 +/- 3.9% (n = 16), 13.9 +/- 4.3% (n = 9) and 32.1 +/- 8.3% (n = 12), 36.8 +/- 8.2% (n = 7) and 48.0 +/- 11.8% (n = 6), 7.7 +/- 3.5% (n = 9) and 18.1 +/- 3.8% (n = 14) from the control. Sequential applications of EAA after glycine or GABA as well as the applications of EAA-agonist and glycine (GABA) mixture demonstrated similar results. The decrease of EAA-responses by glycine and GABA was abolished by selective GlyR antagonist strychnine (1 microM) and the selective GABAR antagonist SR95531 (gabazine, 20 MM), respectively. The data revealed differences in inhibitory effect of glycine and GABA on the excitation responses mediated by different types of glutamate receptors in the frog motoneurones: the predominant inhibitory effect of glycine and GABA on NMDA-responses and weak inhibitory effect on KA- and GLU-responses. Inhibitory effect of glycine was twice as much as that of GABA at the same concentration.