Formation of electrical connections between cultured identified neurons and muscle fibers of the snail Helisoma.

We studied the formation of connections between identified neurons removed from the buccal ganglion of the snail Helisoma and muscle fibers dissociated from the buccal mass. Three types of identified neurons--B19, B5, and B4--were placed into cell culture and muscle fibers from the supralateral tensor muscle (SLT), normally innervated by B19, were subsequently plated adjacent to the neuronal cell bodies. Growth cones from the neurons contacted the muscle fibers within 6-12 h after isolation. Simultaneous intracellular recordings from the neuronal cell bodies and muscle fibers after 4 days in culture indicated that the neurons had formed electrical connections with the fibers. All 3 types of neurons coupled to the muscle fibers but displayed differing probabilities and strengths of connections. The role of growth cone contact in the formation of these connections was tested by plating muscle fibers onto fields of neurites after neuronal growth had stopped. Under these conditions, neurons still became electrically coupled to the muscle fibers, but the strength of these connections differed from those formed by neurons and fibers that were plated simultaneously. Thus, quantitative characteristics of electrical connections formed between cultured Helisoma neurons and dissociated muscle fibers are influenced by neuronal identity and the timing of neuronal contacts.