We show that fluorescently tagged ligands with high affinity for their targets can be reversibly unbound by focused laser excitation. By sequential unbinding and relabeling with different colors of α-bungarotoxin, we selectively labeled adjacent pools of acetylcholine receptors (AChRs) at neuromuscular junctions of adult mice. Timelapse imaging in vivo revealed that synaptic AChRs completely intermingle over ∼4 days and many extrasynaptic AChRs are incorporated into the synapse each day. In mice that lacked α-dystrobrevin, a component of the dystrophin-glycoprotein complex, rates of AChR turnover, and intermingling were increased ∼4- to 5-fold. These results demonstrate remarkable molecular dynamism underlying macroscopic stability of the postsynaptic membrane, and establish α-dystrobrevin as a key control point for regulation of mobility and turnover.