Different Sensitivity of Motoneuron Synaptic Inputs in the Frog, Rana ridibunda, to Antagonists of Excitatory Amino Acids

The effects of antagonists of excitatory amino acids (AP-5, kynurenate, and CNQX) on PSP recorded intracellularly in lumbar motoneurons of a preparation of the isolated spinal cord in the frog, Rana ridibunda, in response to activation of three different synaptic inputs (stimulation of DR, RF, and VC or LC) were analyzed. It is shown that the effects of the antagonists were non-uniform in different motoneurons. Inputs of suprasegmental and sensomotor projections substantially differed from each other. A considerable amount of DC-PSP resistant to kynurenate and CNQX was found, whereas the latter regularly inhibited DR-PSP in the same cell. The disynaptic, as judged by its latency, plane-shaped component was always relatively more stable to kynurenate as compared with other components. Unlike kynurenate that inhibited the early and late components, CNQF selectively depressed the early components of DR-PSP.