Figure 5. CB₂R Agonists Mimic and Occlude the AP-Driven Hyperpolarization.

(A–D) Exemplary V_m time courses of wc CA3 PC recordings are shown for the application of 10 μM2-AG (A), 1 μM WIN (B), and 1 μM HU (C) that hyperpolarize CA3 PCs. The hyperpolarizing effect of HU is gone in the CB₂R^−/− (D).

(E and F) The ΔV_m of each recorded cell (circles) and the median and 25^th and 75^th percentiles of the average ΔV_m (E) as well as the percentage of reactive cells (F) are shown for the application of 2-AG in WT (wc, n(N) = 15(5): −5.3, −9.0 to −3.9 mV; 53.3%) and in CB₂R^−/− (pp, n(N) = 5(2): 1.6, 0.5 to 2.2 mV; 0%), WIN in WT (wc, n(N) = 23(15): −4.2, −5.6 to −2.7 mV; 60.9%), HU in WT (wc, n(N) = 20(10): −7.6, −9.7 to −4.9 mV; 60%), HU in CB₂R^−/− (wc, n(N) = 12(3): 0.9, 0.3 to 1.5 mV; 8.3%), HU in Syn-CB₂R^−/− (wc, n(N) = 14(5): 1.4, 0.3 to 3 mV, 0%), and HU in Syn-CB₂R^+/+ (wc, n(N) = 6(4): −7.5, −9 to −5.7 mV; 50%). Note that the filled circles indicate reactive cells. Green, 2-AG; yellow, WIN; blue, HU. Kruskal-Wallis with Dunn’s post-test, p < 0.05 for 2-AG and HU in CB₂R^−/− versus WT.

(G) AM-251 reverses the hyperpolarization induced by 2-AG in n(N) = 3(3) CA3 PCs (−5.3 ± 0.9 mV and −0.9 ± 1 mV, respectively).

(H) The HU-induced hyperpolarization (blue line) occludes further hyperpolarization of CA3 PCs in response to APs (rectangle) and vice versa. Exemplary ΔV_m time courses of CA3 PCs that hyperpolarize in response to HU (left) and AP trains (right) are shown.

(I) Single-occlusion experiments (gray circles) and mean ± SEM (black) are shown for each condition. Average ΔV_m for HU followed by APs (left, n(N) = 6(4): −6.6 ± 1.3 and −7.8 ± 1.9 mV; paired t test, p = 0.24) and APs followed by HU (right, n(N) = 6(6): −4.2 ± 1.2 and −3.4 ± 0.9 mV, p = 0.19).