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. Author manuscript; available in PMC: 2010 Nov 1.
Published in final edited form as: Neuron. 2010 May 27;66(4):493–500. doi: 10.1016/j.neuron.2010.04.012

Figure 3.

Figure 3

Application of muscimol+ cocktail blocks polysynaptic transmission but preserves monosynaptic excitation in visual cortex in vitro. (A–C) Current-clamp recordings of postsynaptic potentials evoked by WM stimulation. Neurons were maintained at −40 mV, just below spiking threshold, to clearly resolve EPSPs and IPSPs. (A) Overlay of averaged PSP waveforms before (black) and after bath application of SCH50911 (blue), muscimol+SCH cocktail (green), and CNQX (orange). (B) Normalized PSP amplitudes as a percentage of baseline (± SEM) before and after drug cocktail application. EPSP and IPSP amplitudes are not changed by SCH50911 application; EPSP amplitude is significantly reduced in the presence of muscimol+SCH (n = 11, p = 0.002), while IPSPs are completely eliminated (n = 11, p < 0.0001). Further application of CNQX abolished the remaining EPSP (n = 11, p < 0.0001). (C) Averaged time to peak (± SEM) latencies of the EPSPs remain unchanged by the application of SCH50911 alone or muscimol+SCH (n = 11). (D) Averaged FP waveforms before (black) and after bath application of SCH50911 (70 μM) (blue), muscimol (50 μM) +SCH50911 (green), and CNQX (10 μM) (orange). Scale bar: 25 μV, 25 ms. (E) Normalized FP amplitude as a percentage of baseline (± SEM) before and after drug cocktail application. FP amplitude is not changed by SCH50911 application, but is significantly reduced in the presence of muscimol+SCH (n = 9, p < 0.0001). CNQX completely abolishes the remaining synaptic FP (n = 5, p < 0.0001). The short latency FP (< 3 msec) observed in CNQX is not synaptic, as it persists in 0 Ca2+ and under total pharmacological blockade of excitatory synaptic transmission (Bear et al., 1992; Kimura et al., 1989). This response is excluded from analysis. (F) Averaged time to peak (± SEM) latencies of the synaptic FP remain unchanged by the application of SCH50911 alone or muscimol+SCH. (B,E) The grey line, indicating the limit of detection in our measurements, is the mean ± SEM fluctuation in voltage measured 5 ms prior to electrical stimulation (3.47% ± 0.62 for B and 18.5% ± 1.67 for E) taken across 5 ms prior to electrical stimulation.