The α1-AR LTD is initiated by the activation of postsynaptic α1-ARs. A, Summary graph of the amplitude of IPHE induced by PHE (100 μm) and recorded with an internal solution containing GTP (red circles, n = 8) or GDPβS (white circles, n = 8). Postsynaptic intracellular application of the G-protein inhibitors GDPβS abolishes the IPHE. B, Blockade of postsynaptic G-protein signaling prevents the induction of the α1-AR LTD. Bottom, Summary graph of the PHE-LTD recorded with an internal solution containing GTP (0.25 mm, white circles, n = 10) or GDPβS (0.25 mm, red circles, n = 8). Top, Superimposed AMPAR-EPSCs (average 30 trials) recorded with GTP, or GDPβS containing internal solution and collected before (1) and during (2) PHE-LTD. Calibration: 50 pA, 10 ms.