Papers of the Week

Mu-opioid receptor (MOR) signaling regulates multiple neuronal pathways, including those involved in pain, reward, and respiration. To advance the understanding of MOR's roles in pain modulation, there is a need for high-throughput screening methods of opioids in vitro and high-resolution mapping of opioids in the brain. To fill this need, we designed and characterized a genetically-encoded fluorescent reporter, called S ingle-chain P rotein-based O pioid T ransmission I ndicator T ool for M OR (M-SPOTIT). M-SPOTIT represents a new and unique mechanism for fluorescent reporter design and can detect MOR activation, leaving a persistent green fluorescence mark for image analysis. M-SPOTIT shows an opioid-dependent fluorescence turn-on up to 12.5-fold and is able to detect as fast as a 30-second opioid exposure in cell culture. Additionally, it showed an opioid-dependent fluorescence turn-on up to 4.2-fold in neuronal culture and can detect fentanyl with an EC 50 of 15 nM. M-SPOTIT will be useful for high-throughput detection of opioids in cell cultures and potentially a cellular-resolution detection of opioids in vivo. M-SPOTIT's novel mechanism can be used as a platform to design other G-protein coupled receptor-based sensors.