Fig. 4.

I-LTD requires activation of a presynaptic Ca²⁺-dependent phosphatase. (A) In slices pretreated for 1–2 h with the CaN blocker FK506 (50 μM), TBS (arrow) failed to induce I-LTD even with rescue stimulation after TBS (bar), as in Fig. 1. This protocol produced normal I-LTD both with FK506 in the postsynaptic pipette (FK post) and in the solvent alone. Summary bar graph at right for I-LTD in FK506 (bath applied and in postsynaptic pipette), as well as in CyA, compared with appropriate solvent controls for each drug. Time course for I-LTD in CyA shown in Fig. S7A. (B) Similarly, WIN paired with bursts of extracellular stimulation fails to persistently depress fIPSPs in the presence of FK506 (protocol as in Fig. 1D). (C) Okadaic acid (1 μM), which inhibits PP1/2A, had no effect on the magnitude of I-LTD. (D) (Left) mIPSC frequency is significantly increased when the CaN blocker FK506 (50 μM) is washed in. (Right) Average mIPSC amplitude remained constant over this time period. Vehicle treatment did not affect either mIPSC frequency or amplitude (see SI Methods).