Target Cells Promote the Development and Functional Maturation of Neurons Derived from a Sympathetic Precursor Cell Line

The role of target interactions in the development and functional maturation of peripheral neurons was investigated using an immortalized sympathetic precursor cell line. bMAH cells underwent neuronal differentiation in response to neurotrophic factors, but maintained an immature neuronal phenotype characterized by small cell bodies and continued cell division. Co-culture with cardiac myocytes, a target of sympathetic innervation, promoted the appearance of large-diameter postmitotic bMAH neurons. Analysis of bMAH maturation in the presence and absence of co-cultured myocytes indicated that myocyte-derived factors promoted the survival of maturing bMAH neurons prior to their acquisition of nerve growth factor dependence. Myocyte interactions also promoted the functional maturation of bMAH neurons, leading to an increase in the localization of synaptic vesicle proteins into neuritic varicosities and the acquisition of sympathetic-like intrinsic electrical properties. Like primary sympathetic neurons, mature bMAH neurons formed functional connections to cardiac myocytes as measured by evoked postsynaptic responses in connected myocytes. The effects of myocyte co-culture on developing bMAH neurons could be mimicked by myocyte conditioned medium, indicating that cardiac myocytes produce soluble factors that promote the appearance of mature neurons. These experiments indicate that targets of innervation play a role in directing the development and final maturation of peripheral neurons.