Fig. 2.
Tonic inhibition of MC-GC synapses is ligand independent and involves the βγ but not the αi/o limb of the CB1R. (A) Bath application of the CB1R competitive antagonist NESS0327 (0.5 μM) did not increase MC-GC transmission (Bottom, 106 ± 5% of baseline, n = 8, P = 0.1945, paired t test) but blocked DSE (Top, Control: 62 ± 3% of baseline, n = 7; NESS0327: 93 ± 5% of baseline, n = 6; Control versus NESS0327: P < 0.01, Mann–Whitney U test). (B) Rat hippocampal slices were incubated (>1 h) and perfused with the diacylglycerol lipase-α inhibitor THL (10 µM), while incubation and perfusion with the vehicle DMSO served as Control. THL had no effect on the AM251-mediated enhancement of MC-GC synaptic transmission (Bottom, Control: 143 ± 8% of baseline, n = 6; THL: 137 ± 15% of baseline, n = 8; Control versus THL: P = 0.5090, unpaired t test) but blocked DSE (Top, Control: 54 ± 7% of baseline, n = 7; THL: 91 ± 4% of baseline, n = 6; Control versus THL: P < 0.01, Mann–Whitney U test). (C) Bath application of the βγ limb inhibitor gallein (75 μM) reversibly increased MC-GC transmission (Bottom, 140 ± 4.3% of baseline, n = 7, P < 0.001, paired t test). DSE was blocked by gallein (Top, Control: 67 ± 4% of baseline, n = 8; Gallein: 99 ± 4% of baseline, n = 8; Control versus Gallein: P < 0.001, unpaired t test). (D) Gallein-mediated enhancement of MC-GC transmission was accompanied by a significant reduction in PPR (baseline: 1.01 ± 0.06; Gallein: 0.92 ± 0.06%, n = 8; P < 0.01, paired t test) and CV (baseline: 0.21 ± 0.02; Gallein: 0.14 ± 0.02, n = 8; P < 0.01, paired t test). (E) Gallein had no effect on MC-GC transmission when applied in the presence of 5 μM AM251 (106 ± 3% of baseline, n = 7; P = 0.0760, paired t test). (F) The specific αi/o inhibitor NF-023 (10 μM) had no effect on MC-GC transmission (99 ± 4% of baseline, n = 13, P = 0.7147, paired t test). **P < 0.01.