A. In this representative neuron, SR1 (2 μM) markedly increased IPSP amplitude. RMP was -79 mV. B. On average, SR1 increased inhibitory transmission to 133% of control. C. Top: in this CeA neuron, a PPF paradigm revealed that SR1 increased the first IPSP but had little effect on the second IPSP. Bottom left: traces superimposed and scaled to the first IPSP, magnifying the PPF decrease elicited by SR1. Bottom right: on average, SR1 decreased PPF to 76% of control, indicating a tonic presynaptic effect of eCBs to decrease GABA release. D. Verification of CB1 involvement in the effect of WIN2. SR1 (applied at t = 0) increased mean IPSP amplitude to 132% of control and subsequent application of 2 μM WIN2 (t = 20) did not affect IPSPs, which remained at 127% of control, demonstrating that WIN2 decreased IPSPs solely via CB1. E. AM251 (2 μM) applied alone increased IPSP amplitude similarly to SR1 and prevented the action of 2 μM WIN2. RMP was -72 mV. F. On average, AM251 increased inhibitory transmission to 136% of control, and subsequent addition of WIN2 non-significantly decreased IPSPs to 130% of pre-AM251 values.