5-HT elicits a large outward current in the PFC L5 pyramidal neurons from 15q dup mice. a Electrophysiological differences in the membrane properties among L5 pyramidal neurons in the PFC. Upper traces (Sag(+)) were obtained from putative pyramidal tract neurons, while lower traces (Sag(−)) were obtained from putative intratelencephalic neurons in male mice. According to our criteria, more than 3 mV of the sum of the voltage sag and rebound depolarization with the current-injection of − 50 pA are defined as “Sag(+)” pyramidal neurons. b Representative traces of 5-HT-induced outward current obtained from male “Sag(+)” pyramidal neurons by bath-application of 5-HT (20 μM for 30 s). Bars indicate the timing of exogenous application of 5-HT. c The amplitudes of 5-HT-induced outward currents were neuronal type-dependent in male mice of both genotypes (WT: open circles; 15q dup: filled circles). Sag(+) pyramidal neurons display significantly larger 5-HT-induced outward currents in the 15q dup mice (WT: 36.18 ± 4.33 pA, n = 39; 15q dup: 58.01 ± 4.53 pA, n = 45, t (101) = 4.31, p = 8.5 × 10− 5; Steel-Dwass multiple comparison test). On the other hand, Sag(−) pyramidal neurons between genotypes were not significantly different (WT: 12.44 ± 4.53 pA, n = 10; 15q dup: Sag(−): 18.55 ± 4.02 pA, n = 11, p = 0.33; Steel-Dwass multiple comparison test). d Female mice Sag(+) pyramidal neurons displayed a similar extent of 5-HT1A receptor-mediated currents (WT (open circles): 49.41 ± 7.98 pA, n = 22; 15q dup (filled circles): 40.51 ± 7.68 pA, n = 17, t (39) = 0.79, p = 0.43). Bar graphs represent mean ± S.E.M.