Benzophenanthridine alkaloid, piperonyl butoxide and (S)-methoprene action at the cannabinoid-1 receptor (CB1-receptor) pathway of mouse brain: Interference with [3H]CP55940 and [3H]SR141716A binding and modification of WIN55212-2-dependent inhibition of synaptosomal l-glutamate release
Abstract Benzophenanthridine alkaloids (chelerythrine and sanguinarine) inhibited binding of [ 3 H]SR141716A to mouse brain membranes (IC 50 s: 50 s: 21 and 63 µM respectively). Benzophenanthridines and piperonyl butoxide were more selective towards brain CB 1 receptors versus spleen CB 2 receptors. All compounds reduced B max of [ 3 H]SR141716A binding to CB 1 receptors, but only methoprene and piperonyl butoxide increased K d (3–5-fold). Benzophenanthridines increased the K d of [ 3 H]CP55940 binding (6-fold), but did not alter B max . (S)-methoprene increased the K d of [ 3 H]CP55940 binding (by almost 4-fold) and reduced B max by 60%. Piperonyl butoxide lowered the B max of [ 3 H]CP55940 binding by 50%, but did not influence K d . All compounds reduced [ 3 H]SR141716A and [ 3 H]CP55940 association with CB 1 receptors. Combined with a saturating concentration of SR141716A, only piperonyl butoxide and (S)-methoprene increased dissociation of [ 3 H]SR141716A above that of SR141716A alone. Only piperonyl butoxide increased dissociation of [ 3 H]CP55940 to a level greater than CP55940 alone. Binding results indicate predominantly allosteric components to the study compounds action. 4-Aminopyridine-(4-AP-) evoked release of l -glutamate from synaptosomes was partially inhibited by WIN55212-2, an effect completely neutralized by AM251, (S)-methoprene and piperonyl butoxide. With WIN55212-2 present, benzophenanthridines enhanced 4-AP-evoked l -glutamate release above 4-AP alone. Modulatory patterns of l -glutamate release (with WIN-55212-2 present) align with previous antagonist/inverse agonist profiling based on [ 35 S]GTPγS binding. Although these compounds exhibit lower potencies compared to many classical CB 1 receptor inhibitors, they may have potential to modify CB1-receptor-dependent behavioral/physiological outcomes in the whole animal.