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

Benzophenanthridine alkaloids (chelerythrine and sanguinarine) inhibited binding of [3H]SR141716A to mouse brain membranes (IC50s: <1 µM). Piperonyl butoxide and (S)-methoprene were less potent (IC50s: 21 and 63 µM respectively). Benzophenanthridines and piperonyl butoxide were more selective towards brain CB1 receptors versus spleen CB2 receptors. All compounds reduced Bmax of [3H]SR141716A binding to CB1 receptors, but only methoprene and piperonyl butoxide increased Kd (3–5-fold). Benzophenanthridines increased the Kd of [3H]CP55940 binding (6-fold), but did not alter Bmax. (S)-methoprene increased the Kd of [3H]CP55940 binding (by almost 4-fold) and reduced Bmax by 60%. Piperonyl butoxide lowered the Bmax of [3H]CP55940 binding by 50%, but did not influence Kd. All compounds reduced [3H]SR141716A and [3H]CP55940 association with CB1 receptors. Combined with a saturating concentration of SR141716A, only piperonyl butoxide and (S)-methoprene increased dissociation of [3H]SR141716A above that of SR141716A alone. Only piperonyl butoxide increased dissociation of [3H]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 [35S]GTPγS binding. Although these compounds exhibit lower potencies compared to many classical CB1 receptor inhibitors, they may have potential to modify CB1-receptor-dependent behavioral/physiological outcomes in the whole animal.