Figure 4. Effects of glutamate on tonic frequency gain.

A and B, firing discharge of a high-recruitment current motoneuron in response to two different current steps in control (A) and glutamate (B) conditions. C, plot illustrating the relation between the coefficient of variation of the interspike intervals measured at different firing rates and stimulating current intensities. D, plots of the steady-state frequency against current intensity (I–F plots) for a motoneuron in control (C) and glutamate (D) conditions. It should be noted that this motoneuron showed an increase in tonic frequency gain and a decrease in recruitment threshold current in the glutamate condition.