Fig. 3. mEPSCs at mature excitatory spinal synapses are mediated by both AMPA-R and NMDA-R. A, B, GYKI and Mg2+ selectively block the fast and slow mEPSC components, respectively. A, Continuous traces of mEPSCs recorded at −70 or +60 mV, as indicated. B, Mean mEPSCs are shown for each corresponding segment of the recording.a, Dual-component mEPSCs predominate in control 0-Mg2+ saline. b, GYKI blocks fast mEPSCs and the fast component of dual mEPSCs; the mean mEPSC has a slow decay constant comparable to the slow component of the mean dual mEPSC in a. c, In the continued presence of GYKI the addition of Mg2+ blocks all mEPSCs at −70 mV (lower trace), although occasional single channel openings of 4–5 pA are observed that may be attributable to synaptic NMDA-R. At depolarized potentials (+60 mV; upper trace), outward mEPSCs with prolonged decay constants are evident. These results indicate that fast mEPSC components are mediated by AMPA-R, and the slow component is mediated by NMDA-R. d, Both dual-component and fast mEPSCs are recorded after >8 min washout of GYKI and Mg2+. C, D, APV selectively abolishes the slow mEPSC component. Traces (C) and averaged mEPSCs (D) at −70 mV are illustrated as in A and B.a, Dual-component and fast mEPSCs recorded in control 0-Mg2+ saline. b, In the presence of APV and GYKI all mEPSCs are abolished. c, After the washout of GYKI in the continued presence of APV, only fast mEPSCs are observed, which are indistinguishable from fast mEPSCs observed in control saline. A, B and C, D were recorded from two cells in different mature 7 d larvae; the recording in A and B was made in the presence of 10 μm glycine, which did not change the distributions of mEPSCs significantly (n = 4). Mean fast mEPSCs are averages of 7–21 events; other mean mEPSCs are averages of >50 events.