CNR1 and amyotrophic lateral sclerosis: Therefore, another 11C-labeled analog was synthesized, which did show increased binding to ALS patient tissue compared with control tissue, but in vivo in mice [11C]RS-028 (Figure 2, Ki = 0.8 nM, >10,000 selective over CB1) showed rapid washout of spleen (high abundance of CB2) and low brain uptake, leading authors to conclude this tracer is not optimal for in vivo application [24].