(A) Images of 12–14 DIV hippocampal cultures of Gad67+/GFP mice. In the upper panel, under fluorescent illumination, GABAergic neurons appear green, and were stimulated (Sti) while recording from nearby glutamatergic cells (Rec) and puffing solutions (puff, lower panel DIC). Scale bar: 10 µm. (B) Sample traces showing postsynaptic uIPSC responding to presynaptic action potentials induced by short depolarizing voltage pulse injection (2 ms) to GABAergic neurons. (WT, black line; App-/-, red line). (C) Quantification of uIPSC amplitude shows a significant decrease in App-/- mice. (WT, n = 18 cells from five mice; App-/-, n = 17 cells from five mice). (D) Sample traces showing uIPSC recordings responding to injection of paired pulses to presynaptic GABAergic neurons (100 ms interpulse interval, left trace and 150 ms interpulse interval, right trace). (E) Quantification of paired pulse ratio (PPR) of uIPSCs with 100 ms and 150 ms interpulse intervals shows no significant difference between genotypes. (F) Sample traces showing evoked inhibitory currents responses to puffing 100 µM isoguvacine. (G) Quantification of isoguvacine-evoked inhibitory current amplitudes shows a significant decrease in App-/- mice. (WT, n = 14 cells from three mice; App-/-, n = 14 cells from three mice). (H) Representative immunoblots of hippocampal extracts from WT and App-/- littermates. (I) Quantification of the immunoblots reveals a significant decrease of GABAAR α1, but not other GABAAR subunits, levels in App-/- mice. Representative immunoblots of western blotting were from single experiment using three pairs hippocampal lysates, two repeats. *p<0.05; Student’s t-test.