[Properties of the response of frog motoneurons to glutamate application].

The reversal potential (E) of the glutamate response produced by iontophoretically applied glutamate and that of the EPSP's recorded from three synaptic inputs produced by reticular formation (RF), dorsal roots (DS), and microstimulation of presynaptic terminals (PT) at the point of glutamate application were compared at the same motoneuron of the isolated frog spinal cord using current-chop technique. Following Cs injection the glutamate response and EPSP's were reversed. Different points of glutamate application were tested. Mean values of E were: Eglu = -16.9 +/- 1.7 mV (n = 13), EPT = -15.1 +/- 1.4 mV (n = 13), ERF = -6.8 +/- 1.7 mV (n = 13), EOR = -9.8 +/- 1.8 mV (n = 6). The summation of the glutamate responses and EPSP was close to linear. Increase of the input conductance did not exceed 10%. The results obtained suggest that glutamate induces depolarization via the receptors of the postsynaptic membrane and may serve as a neurotransmitter in all of the studied inputs.