Inset, Drugs were administered during the 10 day period (PND 35–44) following puberty onset (vaginal opening, VO, ~PND35) when α4βδ GABAR expression is increased (Shen et al., 2007, 2010). Electrophysiology was performed at the end of the injection period (PND 44). Spine density and behavior were evaluated on PND 56. GBX, gaboxadol (THIP), a GABAR agonist with selectivity at α4βδ GABARs at low doses; VEH, vehicle (oil); THP, 3α-OH-5α-pregnan-20-one, a GABAR modulator which decreases α4βδ expression during puberty (Shen et al., 2007). A–B, Effect of pubertal drug or vehicle treatment on whole cell voltage clamp responses of CA1 pyramidal cells to 100 nM GBX, a reflection of α4βδ expression. A, averaged data (mean ± S.E.M). *ANOVA, F(2,12)=14.93, P ≤ 0.001 vs. other groups; B, representative currents. n=5 cells (mice)/group. Scale bars, 50 s (timebase), 50 pA (amplitude)