Fig. 2. Insertion of newly recycled AChRs matches the removal of recycled receptors. (A) The sternomastoid muscle was labeled with BTX-biotin followed by a saturating dose of strept-488. Three to 4 days later, the animal was anaesthetized and the sternomastoid muscle bathed with a saturating dose of strept-594 to specifically label the recycled receptors; superficial synapses were imaged immediately, and again 2 days later, and the loss of recycled receptors determined. The sternomastoid muscle was then bathed with fresh strept-594, and the synapses re-imaged to determine the insertion of newly recycled AChRs. Scale bar, 20 µm. (B) Bar graph summarizing the recycled AChR loss and insertion results (±s.d.) obtained by the approach shown in A. Note that nearly all of the AChRs from the recycled pool lost over the 2 days were replaced by newly recycled receptors re-inserted into the postsynaptic membrane of the NMJ.