Fig. 3.

Synaptic NRG expression resumes after reversal of activity blockade. Chicken embryos were treated with either paralytic concentrations of curare (3 mg/d) or the same volume of saline from E14 to E17. Some of the embryos were examined on E17, showing that activity blockade blocked the appearance of NRG immunoreactivity compared with untreated embryos that expressed submaximal, synaptic NRG levels. All muscle sections were double-labeled at the same time with 183N antibodies against NRG and α-bungarotoxin (BTX) for localization of synapses. Each group was either continued with the same treatment or switched to the opposite treatment from E17 to E19. Those that were in saline for the entire period from E14 to E19 had maximal NRG staining, whereas curare treatment from E17 to E19 prevented any additional increase in NRG staining. Those animals maintained in curare for the entire period had no NRG staining at synapses, whereas those switched from curare to saline recovered their ability to release NRG at synapses. Scale bar, 20 μm.