Regulation of cannabinoid CB receptor constitutive activity in vivo: repeated treatments with inverse agonists reverse the acute activation of JNK and associated apoptotic signaling in mouse brain

Rationale: CB receptors express constitutive activity and inverse agonists regulate receptor basal activity, which might be involved in death mechanisms. This study assessed the effects of a selective CB agonist (JWH133) and different CB inverse agonists (AM630, JTE907, raloxifene) on death pathways in brain. Objectives: The acute (JWH13) and the acute/chronic effects (AM630, JTE907, raloxifene) of CB ligands regulating pro-apoptotic c-Jun NH-terminal kinase (p-JNK/JNK ratio) and associated signaling of extrinsic (Fas receptor, Fas-Associated death domain protein, FADD) and intrinsic (Bax, cytochrome c) death pathways (nuclear poly (ADP-ribose) polymerase PARP) were investigated in mouse brain. Methods: Mice were treated with CB drugs and target protein contents were assessed by western blot analysis. Results: JWH133 reduced cortical JNK (−27–45%) whereas AM630 acutely increased JNK in cortex (+61–148%), cerebellum (+34–40%), and striatum (+33–42%). JTE907 and raloxifene also increased cortical JNK (+31%–57%). Acute AM630, but not JWH133, increased cortical FADD, Bax, cytochrome c, and PARP cleavage. Repeated treatments with the three CB inverse agonists were associated with a reversal of the acute effects resulting in decreases in cortical JNK (AM630: −36%; JTE907: −25%; raloxifene: −11%). Chronic treatments also induced a reversal with down-regulation (AM630) or only tolerance (JTE907 and raloxifene) on other apoptotic markers (FADD, Bax, cytochrome c, PARP). Conclusions: AM630 and JTE907 are CB protean ligands. Thus, chronic inverse agonists abolished CB constitutive activity and then the ligands behaved as agonists reducing (like JWH133) JNK activity. Acute and chronic treatments with CB inverse agonists regulate in opposite directions brain death markers.