Figure 4. LTD in NTS neurons requires activation of CB1Rs. A, Blockade of CB1Rs with AM251 does not alter EPSC amplitude during baseline recordings. Normalized EPSC amplitudes for all neurons recorded before and after AM251 application. B, Normalized individual response amplitudes to stimulation of visceral afferent fibers (TS stimulation; gray circles) recorded before and after LTD induction by LFS during blockade of CB1Rs. In this condition, LFS does not induce LTD in this neuron. C, Normalized EPSC amplitudes for all neurons recorded in the presence of AM251 before and after LFS. Note that, after a transient depression, EPSC amplitude reverted to nearly control amplitude. D, Absence of changes in PPR an CV before (CONT) and after LFS in NTS neurons in the presence of AM251. E, Comparison of LTD amplitude in the control group in the presence of APV, AM251, or both. Note that blockade of both NMDARs and CB1Rs do not better suppress LTD that APV or AM251 alone, arguing against an additive effect of NMDARs and CB1Rs on LTD induction. F, Blockade of fatty acid synthesis does not suppress LFS LTD. Normalized EPSC amplitudes for NTS neurons recorded in control condition (black circles, n = 5) or after pretreatment and perfusion with THL (white circles, n = 5; for clarity, each data point represents the amplitude of the average of 3 consecutive EPSC). In both groups, LFS induced a similar LTD. G, Blockade of FAAH with JNJ lowers the threshold for LFS LTD induction. Normalized EPSC amplitudes for NTS neurons recorded in before and after 0.5 min LFS (black circles, n = 8) or after pretreatment and perfusion with JNJ (white circles, n = 6; for clarity, each data point represents the amplitude of the average of 3 consecutive EPSCs). Note that, in control conditions, 0.5 min LFS of visceral afferent fibers did not induce LTD, whereas a prominent depression was observed after JNJ treatment. H, Same experiment as in G but with control LFS (4 min). Note that, in the untreated control group (n = 7), LTD reached gradually a maximum value within 50 min after LFS, whereas in the JNJ group (n = 5), maximum LTD is already reached after LFS. Gray lines, Exponential fits for LTD time course after LFS in both groups. Exponential equation is f(t) = a × exp(−b × t). a and b are equal to 0.77 and 0.05 for the control group and to 0.44 and 0 for the JNJ group, respectively.