In postganglionic sympathetic neurons, the size of the dendritic arbor determines presynaptic convergence, which correlates with tonic activity, and aberrant dendritic morphology is associated with disease. There is, therefore, great interest in understanding how dendritic morphology is regulated in these neurons. Early studies established a role for target-derived nerve growth factor (NGF) in regulating the size of the dendritic arbor of sympathetic neurons in vivo. However, in vitro studies revealed that even in the presence of optimal concentrations of NGF, rat sympathetic neurons cultured in the absence of serum or non-neuronal cells survive and elaborate extensive axonal arbors, but fail to form dendrites. Subsequently, it was discovered that bone morphogenetic proteins (BMPs) trigger cultured sympathetic neurons to extend a dendritic arbor comparable to that of their in vivo counterparts. The goals of this chapter are to: (i) summarize these early experiments; (ii) discuss evidence substantiating a role for BMPs in glial-induced dendritic growth in vitro and regulation of dendritic growth in vivo; (iii) review what is known about the molecular mechanisms by which NGF, BMPs and other factors influence dendritic arborization of sympathetic neurons; and (iv) identify key data gaps in understanding of how dendrites are regulated in sympathetic neurons.
Part of the book: Autonomic Nervous System