Figure 2

Propofol suppresses temporal summation via a shunting mechanism. A: (left) control EPSP summation was recorded as described for Fig. 1C. Bath application of propofol (3 μM, 20 min) markedly decreased EPSP amplitude and summation (middle). Overlay (right) comparing EPSPs in the absence and presence of propofol. B: overlay (left) comparing voltage responses elicited by a hyperpolarizing current pulse (-60 pA, 500 ms, not shown) in the absence (control, thin line) and presence of propofol (thick line) in the same neuron as in A. Note that propofol decreased apparent input resistance. Bar graph (right) showing that propofol significantly decreases input resistance. *: P < 0.05, n = 15. Time scales: 100 ms for A and 300 ms for B. C: control EPSPs were recorded from a different VB neuron. Overlay (left) comparing EPSPs in the absence (control) and presence of the GABA_A antagonist bicuculline (10 μM). Overlay (right) comparing EPSPs in the presence of bicuculline alone and bicuculline + propofol (3 μM). In the presence of bicuculline, propofol had no significant effect on temporal summation, indicating propofol-elicited shunting inhibition was mediated by GABA_A receptors in VB neurons. D: group data showing that propofol decreases temporal summation through potentiation of GABA_A receptors. *: P < 0.05, one-way ANOVA, vs. control. n = 15/each group. prop = propofol (0.6, 0.3 μM), bic = bicuculline (10 μM).