A novel paramagnetic probe for in-vivo MRI imaging of cannabinoid-1 receptor in the mouse brain

Motivation: Localization of Cannabinoid type I receptor (CB1) across the whole brain with high temporal and spatial resolution would help a fundamental understanding of this receptor. Goal(s): We sought to develop an in vivo MRI probe suitable for the cannabinoid system. Approach: By chemically conjugating Rimonabantacid to the gadolinium chelate, we sought to create a novel paramagnetic probe TC1648·Gd. Introduction of this drug into mouse brains furthermore permits MRI-based measurement. Results: Comparing the PET results with the TC1648.Gd, the high expression of CB1 in the hippocampus and the poor expression in the hypothalamus are highly consistent. TC1648.Gd enable imaging-based assessment of distribution of CB1. Impact: The reagent is straightforward to produce and apply, and could immediately be used in a range of preclinical biomedical contexts. In future work, the idea of conjugating paramagnetic moieties to neuromodulatory agents could be extended to create additional MRI-detectable probes.