Neurotransmitter receptor dynamics studied in vivo by reversible photo-unbinding of fluorescent ligands.

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 alpha-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 approximately 4 days and many extrasynaptic AChRs are incorporated into the synapse each day.