Fig. 3.

eCB-mediated LTD requires presynaptic, but not postsynaptic Ca²⁺. (A) DHPG does not induce I-LTD when coapplied with a Ca²⁺-free (0 Ca²⁺) recording solution. In the same cell, a subsequent DHPG application under normal recording conditions successfully triggers I-LTD. (B) Pretreating slices with 100 μM EGTA-AM and washing it out before TBS significantly attenuated I-LTD, compared with I-LTD induced with 20 mM BAPTA added to the recording pipette. (C) Depleting intracellular Ca²⁺ stores with either 30 μM bath-applied CPA or 2 μM TG prevents I-LTD induction. (D) Incubating slices with CPA also blocks the persistent depression of fIPSPs produced by WIN paired with extracellular burst stimulation (protocol as in Fig. 1D).