Specificity of synapse formation between Lymnaea heart motor neuron and muscle fiber is maintained in vitro in a soma-muscle configuration.

Precise neuronal connectivity during development is subservient to all nervous system functions in adult animals. However, the cellular mechanisms that mastermind this neuronal connectivity remain largely unknown. This lack of fundamental knowledge regarding nervous system development is due in part to the immense complexity of mammalian brain, as cell-cell interactions between defined sets of pre- and postsynaptic partners are often difficult to investigate directly. In this study, we developed a novel model system which has allowed us to reconstruct synapses between identified motor neurons and their target heart muscle cell in a soma-muscle configuration. Utilizing this soma-myocardial cell synapse model, we demonstrate that synapses between somata and heart muscle cells can be reconstructed in cell culture. The soma-myocardial cell synapses required 12-24 h to develop and thus differed temporally from conventional neuromuscular synapses (seconds to a few minutes). We also demonstrate that the synapses are target cell-type-specific and are most likely independent of transmitter phenotypic characteristics of presynaptic neurons.