Acetylcholine release from growth cones detected with patches of acetylcholine receptor-rich membranes.

Synaptic potentials can be evoked at nerve-muscle junctions in vitro within minutes after an exploring growth cone contacts a receptive myotube. Functional transmission is also evident in vivo on the time scale of minutes after motor axons enter adjacent myotomes. The ability to release acetylcholine (ACh) may be induced in motor nerve terminals after they contact receptive target cells. Alternately, growth cones may be capable of releasing ACh before contact. To examine the development of ACh release we have used isolated patches of acetylcholine receptor(AChR)-rich membrane as sensitive detectors of ACh. We report here that the growth cones of embryonic chick ciliary ganglion neurones can release ACh, even when the cells are grown in the absence of target myotubes.