Figure 8. Retrograde Signaling at the NMJ.

Model for retrograde signaling at the NMJ in wild type and mutant mice. ACh release from the presynaptic nerve terminal leads to a retrograde signal from muscle in the form of an activity-independent “go” signal promoting growth of the neurite and an activity-dependent “stop” signal halting neurite growth. The “stop” signal is dominant over the “go” signal. In wild type embryos the “stop” signal prevents further growth of the neurite once an endplate is formed. In the absence of postsynaptic activity, the “stop” signal does not occur and the activity-independent “go” signal triggers continuous neurite growth with the formation of additional endplates on the same muscle fiber.