Figure 7.
Effects of neostigmine on the EPSCs. A, Single traces of a 5p-EPSC before (Control) and 5 min after addition of neostigmine (1 μm). The holding current increased and the decay of the EPSC was greatly prolonged; note the increased noise of the holding current. B, Analysis of the decay of the EPSCs before (gray) and in the presence of neostigmine (black); note the logarithmic scale. B1, 1p-EPSCs. B2, 5p-EPSCs. Neostigmine adds to the decay an ultra-slow component (τ3 (1p) = 1741 ± 329 ms; τ3(5p) = 2188 ± 234 ms; n = 6). The time constants describing the 1p-EPSC are unaffected, (1p: τ1(CTL) = 16.1 ± 1.3 ms, τ1(NEO) = 17.8 ± 0.8 ms, p = 0.20; τ2(CTL) = 104.4 ± 10.0 ms, τ2(NEO) = 127.4 ± 19.5 ms, p = 0.40) and the time constants for 5p-EPSCs show a nonsignificant decrease (5p: τ1(CTL) = 27.0 ± 2.7 ms, τ1(NEO) = 24.2 ± 2.2 ms, p = 0.17; τ2(CTL) = 122.3 ± 15.2 ms, τ2(NEO) = 206.2 ± 30.9, p = 0.05). The amplitudes a1 and a2 decreased significantly (1p: a1(CTL) = −293.9 ± 69.6 pA, a1(NEO) = −224.2 ± 64.3 pA, p = 0.01; a2(CTL) = −85.1 ± 16.5 pA, a2(NEO) = −51.6 ± 13.5 pA, p = 0.01) and (5p: a1(CTL) = −273.8 ± 86.7 pA, a1(NEO) = −199.0 ± 64.6 pA, p = 0.03; a2(CTL)= −277.4 ± 44.4 pA, a2(NEO)= −121.4 ± 34.8 pA, p = 0.002). This effect was time dependent (data not shown). C, Steady current induced by neostigmine. Neostigmine (1 μm) induced a progressive increase of the holding current I (C1, top). The amplitude of the additional current, ΔINeo, was −32.6 ± 4.1 pA (n = 19). The subsequent application of DHβE (10 μm) reversed the effect of neostigmine and reduced the holding current by ΔIDHβE = 32.0 ± 5.0 pA (n = 14). The increase of the holding current after addition of neostigmine was associated with an increased variance, and the effect of DHβE with a decreased variance (C1, Bottom, Each point corresponds to the average of the values measured during 200 ms). C2, The elementary current l was calculated as i = Δσ2/ΔI = −1.15 pA.