Neutrophins and neurite outgrowth in the peripheral nervous system

In this review we summarize evidence for the involvement of neutrophins in the regulation of neurite outgrowth in the peripheral nervous system. Recent studies have shown that many neurons at early developmental stages respond to NT3 by increased survival and morphological differentiation in vitro. In addition, NT3 mRNA can be detected at this time in embryonic tissues trespassed by outgrowing neurites. Later during development, the NT3 response may be lost and replaced by a NGF response. The data show that an early NGF-independent, NT3-sensitive and a late NGF-responsive period can be distinguished for different developing peripheral neurons in vitro and raise the possibility that neurite outgrowth may be influenced by the different neutrophins, acting at distinct developmental periods in vivo.