Confident that LUXendin762 was able to specifically label GLP1R, we next injected Nude mice with the probe before imaging. Strong fluorescent signal could be detected in the abdomen and brain at 30 min and 60 min following intraperitoneal or subcutaneous injection, with fluorescence levels ~2-5-fold higher than in animals receiving saline vehicle (Figure ). Harvest of various organs showed the highest fluorescent signal in the pancreas of mice receiving intraperitoneal LUXendin762, with brain, lung, kidney and heart being similar to saline-treated controls (Figure ). By contrast, mice receiving subcutaneous LUXendin762 displayed the highest probe levels in the brain, whereas no signal was detected in the pancreas, lung, kidney and heart versus saline-treated control (Figure ). Notably, the brain and pancreas are known to be GLP1R-positive , whereas protein expression of the receptor in the lung, kidney and heart is in small cell populations (e.g. smooth muscle of arterioles) or absent . Together, these studies show that LUXendin762 signal can be detected in vivo in the whole organism, and reveal a novel role for injection route in determining GLP1R access.