In this work we performed photo-proximity labeling in vivo. A photosensitizer was anchored to a targeted neurotransmitter receptor in the live mouse brain and subsequently conducted photolabeling. This was performed by irradiating the desired brain region following the injection of a biotinylated labeling reagent. Isolated tissue was homogenized and labeled proteins were enriched, subjected to SDS-PAGE, in-gel tryptic digestion and analyzed by LC-MSMS.