Siuda, E.R. et al. Neuron 86, 923–935 (2015).

Despite the clinical interest in opioid drugs, the function of opioid receptors is difficult to study with high spatial, temporal and cell type–specific precision. Siuda et al. generated a light-controlled opioid-like receptor called opto-MOR. This designed receptor is a hybrid between the intensely studied mu-opioid receptor (MOPR) and a rat rhodopsin and is made possible by the structural similarities of the parent molecules. Opto-MOR exhibits expression levels similar to those of MOPR and activates the same signaling pathways when stimulated with blue light. The researchers applied the tool to study the effects of opioid signaling in different regions of the mouse brain. For instance, activation of opto-MOR in the ventral pallidum led to aversive behaviors, whereas the same manipulation in the rostromedial tegmental nucleus had the opposite effect.