NS9283 potentiates and prolongs the slow component of the MN-RC nicotinic eEPSC (A, B) and prolongs the sEPSCs (C). The eEPSCs were elicited by a stimulation of the VR with one pulse (1p, A) or five pulses (5p, 100 Hz, B). The decay was fitted by two exponentials, which defined four parameters: the amplitudes (a1, a2) and the decay time constants (τ1, τ2) of the fast and slow components. The weighted time constant τw combined these four values. A, Effect of NS9283 (10 μm) on a 1p eEPSC. CTL: a1 377 pA, a2 62 pA, τ1 10.2 ms, τ2 129 ms, τw 27 ms. NS9283: a1 300 pA, a2 98 pA, τ1 8.3 ms, τ2 222 ms, τw 60.9 ms. B, Effect of NS9283 (10 μm) on a 5p eEPSC (same cell as in A). CTL: a1 412 pA, a2 132 pA, τ1 13.8 ms, τ2 144 ms, τw 45.4 ms. NS9283: a1 260 pA, a2 291 pA, τ1 10.9 ms, τ2 274 ms, τw 150 ms. C, Effect of NS9283 (10 μm) on sEPSCs (same cell as in A, B). CTL average of 54 events, NS9283 average of 245 events. CTL: a1 −19.7 pA, a2 −1.0 pA, τ1 9.2 ms, τ2 51.2 ms, τw 11.2 ms. NS9283: a1 −16.4 pA, a2 −4.5 pA, τ1 8.8 ms, τ2 76.4 ms, τw 23.3 ms. D, Effects of three concentrations of NS9283 (1, 3, 10 μm) on the values of τ2, a2, τ1, and τw for 1p eEPSCs. The values of the three time constants, which do not vary significantly as a function of the intensity of the VR stimulation, were plotted directly for each NS9283 concentration. For a2, however, the value depends on the intensity of stimulation, which changes the number of axons excited, and this leads to the variability illustrated in the left part of the graph for the control value (Ctrl). To evaluate the effects of NS9283, we plotted the value of the ratio of the amplitude measured in NS9283 over that measured in control (right ordinate scale). For τ1, the values were those measured from the double exponential fit assuming that both components start at time 0, but, as discussed in Materials and Methods, this assumption leads to an apparent decrease, which disagrees with the observation (A, B) that the decay of the early component of the EPSC is not changed by NS9283.
