A, The intrinsic excitability of layer V pyramidal neurons was assessed by examining the frequency of action potentials elicited by injections of depolarizing current. Representative examples are shown from control (Ai) and ES (Aii) animals. B, A graph of the input–output relationships shows that layer V pyramidal cells from both groups have similar excitability when assessed from their resting potentials. C, The frequency of glutamatergic sPSCs measured in layer V pyramidal neurons at baseline and in response to 5-HT (10 μm, 30 s) in controls and ES. Both groups have a similar frequency of glutamatergic sPSCs at baseline. In the presence of 5-HT, the frequency of glutamatergic sPSCs is significantly enhanced in both controls and ES animals, and two-way ANOVA revealed an interaction where by the 5-HT-elicited increase in glutamatergic sPSCs is significantly enhanced in ES neurons (*p = 0.0006). D, The frequency of GABAergic sPSCs measured (with high Cl− patch solution in the presence of CNQX, 20 μm) in layer V pyramidal neurons at baseline and in response to 5-HT (10 μm, 30 s) in controls and ES. Interestingly, ES layer V neurons display a significantly higher frequency of GABAergic sPSCs at baseline (two-way ANOVA reveals a significant main effect of postnatal group, *p = 0.001). Bath application of 5-HT (10 μm, 30 s) did not significantly alter the frequency of GABAergic sPSCs in either the control or ES animals. A higher concentration of 5-HT may be required to increase the frequency of GABAergic sPSCs overall (Zhou and Hablitz, 1999).