Figure 1
Selective increase in miniature inhibitory postsynaptic current (mIPSC) frequency by esmolol in neurons of the caudal part of the spinal trigeminal nucleus (Sp5c). (A) Top: the membrane current recording of an Sp5c neuron at a holding potential of -40 mV. Esmolol was applied at the horizontal bar. Middle: the time course of the changes in miniature excitatory postsynaptic current (mEPSC) frequency with esmolol. Bottom: the time course of the changes in mIPSC frequency with esmolol. The abscissae of these graphs are identical (time; 5 min/div). (B) 1 and 2 are time-extended traces taken at the points 1 and 2 in the trace in A (top). mIPSCs and mEPSCs (outward and inward events, respectively) are marked with open circles above the traces and filled circles below the traces, respectively. (C) and (D) Summaries of the effects of esmolol on mIPSC and mEPSC frequency, respectively. "cont", mPSC frequency observed in 3-min control period before esmolol application (filled markers and bars); "esmo", those at 10-min application of esmolol (500 μM; open markers and bars). The numbers in parentheses indicate the number of neurons tested and were used for the statistics. Left, results of recordings with "CsCl-based" internal solution (squares) under pharmacological isolation of mIPSCs (C) and mEPSCs (D); center, results of recordings with "low-Cl" internal solution in five cells (circles) in which mIPSCs (C) and mEPSCs (D) were simultaneously recorded (see Methods); right bars, pooled summaries based on the results with "CsCl" internal solution and "low-Cl" solution. *, P < 0.05; NS, not significantly different from pre-administration values (100%). Paired t-test. (E) Concentration-response relationship between esmolol and the changes in mIPSC frequency. The curve indicates the best-fit Hill equations for the data for esmolol. The number of neurons used to estimate the mean values and curve-fitting was 39 (control); 5 (5 μM); 5 (50 μM); 4 (100 μM); 35 (500 μM); 7 (1500 μM). *, P < 0.02; Mann-Whitney's U test; vs. control (no drug application). The horizontal broken line indicates the control values (100%).