Effects of carisbamate (CRS) upon excitatory synaptic transmission. CRS (100–400 µmol·L−1) produced a selective, concentration-dependent suppression of depolarizing postsynaptic potentials (DPSPs) evoked by subthreshold lateral olfactory tract (layer Ia, LIa)-afferent fibre stimulation. (A) Superimposed subthreshold LIa DPSPs are elicited in control conditions and in CRS (100 and 250 µmol·L−1 as indicated). (B) Pooled log–concentration response curve showing the inhibitory effect of CRS upon LIa DPSP amplitude, expressed as percentage of control (data points are means ± SEM, n= 6; best-line fit gave EC50= 118 µmol·L−1; data points significantly different from control are indicated by *, P < 0.05).