Figure 3.

Postsynaptic responses to iontophoretic application of glutamate show very small trial-to-trial variability. (A) Families of currents at two stimulus strengths illustrate the consistency in responses to fixed glutamate concentrations. Each family contains 10 individual traces. (B) Amplitude histograms show little variability in amplitude of AMPAR-mediated responses to half-maximal (CV = 0.1) and maximal stimulus strengths (CV = 0.04) for glutamate iontophoresis. (C) Pooled data for the CV of currents evoked by glutamate iontophoresis (CV = 0.1; four separate experiments) compared with the CV for the AMPA component of mEPSCs recorded at single synapses (CV = 0.36; average of all 11 synapses). (D) Glutamate-evoked responses decrease rapidly with lateral movements of the iontophoretic pipette away from the synapse; the response is almost completely abolished with a 1-μm displacement. (E). The maximal amplitude of the average evoked response (pA) to increasing concentrations of iontophoretically applied glutamate at this synapse plateaued at approximately 100 pA.