A-349821

A-349821 is a histamine H3 receptor antagonist characterized as a radioligand ([3H]-A-349821) for in vivo receptor occupancy assessment. In rats, [3H]-A-349821 penetrated the brain, showing higher levels in the cortex compared to the cerebellum, indicating selective H3 receptor binding. Its cortical occupancy was saturable, correlating with in vitro binding data. Inhibition studies with ABT-239 and other H3 antagonists showed dose-dependent reductions in receptor occupancy, matching blood levels associated with cognitive efficacy in preclinical models. [3H]-A-349821 thus serves as a valid tracer for H3 receptor occupancy, aiding in the development and clinical interpretation of H3 receptor antagonists.