The formation of synapses between chick embryo skeletal muscle and ciliary ganglia grown in vitro.

1. Chick embryo ciliary ganglia (explanted) and skeletal muscle (dissociated) were grown together in vitro for up to 3 weeks. Nerve processes sprouted from the ganglia and contacted neighbouring myotubes and striated muscle fibres. 2. Spontaneous action potentials and subthreshold e.p.p.s. were recorded from muscle fibres with intracellular micropipettes. Similar potentials could be evoked by electrical stimulation of the ganglion. The pharmacological effects of curare and tetrodotoxin were identical to those observed at adult vertebrate neuromuscular junctions. 3. The amplitude, but not the frequency, of the spontaneous potentials was affected by changing the muscle fibre membrane potential. The reversal potential of evoked synaptic potentials occurred at a membrane potential of about 0 mV.