A1R activation during the induction phase of glu-LTD is sufficient to block glu-LTD. A, R-PIA (100 nm) application restricted to the period of the conjunctive depolarization/glutamate stimuli blocks glu-LTD. The conjunctive stimuli were 12 sets of simultaneous depolarizing voltage jumps (0 mV, 3 s) and glutamate iontophoresis. Traces indicate sample Iglu of a cell before and after the conjunctive stimuli. Each plot indicates the time course of the mean peak amplitude of Iglu. B, C, R-PIA (100 nm) application before (B) or after (C) the conjunctive stimuli did not affect glu-LTD. D, Summary of the effects of the labeled manipulations on glu-LTD. Columns and error bars, mean ± SEM of the peak amplitudes of Iglu at 40–50 min of the onset of the conjunctive stimuli. E, The effect of R-PIA on glu-LTD was seen in saline containing 2.5 mm KCl and at 30°C. Columns and error bars, mean ± SEM of the peak amplitudes of Iglu at 35 min of the onset of the conjunctive stimuli. Scale bars, 1 s and 100 pA. White bars, timing of the conjunctive stimuli; dots and error bars, mean ± SEM of the data for every 2 min period. *p < 0.05; **p < 0.01.