Neurturin (NTN) is an important
neurotrophic factor for parasympathetic neurons; however, no studies to date have investigated the signalling mechanisms downstream of GFRalpha2 and Ret activation underlying this neurotrophic support. This is particularly important for pelvic parasympathetic neurons, which are prone to injury during
surgical procedures such as
prostatectomy, and where there are no current
therapies for axonal regeneration. To address this issue we have cultured dissociated adult rat pelvic
ganglion neurons and also examined the structural changes in pelvic
ganglion neurons after
axotomy. Axotomised penile neurons deprived of target-derived support had smaller somata than intact neurons. Studies of cultured adult pelvic
ganglion neurons also demonstrated that NTN stimulated
soma growth. Further experiments showed that NTN reduced the up-regulation of
tyrosine hydroxylase expression in cultured pelvic parasympathetic neurons. NTN stimulated the extension of neurites in cultured parasympathetic, but not sympathetic, pelvic
ganglion neurons. Inhibition of
phosphatidylinositol 3-kinase prevented initiation of neurite outgrowth, whereas inhibition of the
mitogen-activated protein kinase and the
Src family kinase pathways disrupted NTN-stimulated microtubule assembly. Surprisingly, NTN did not activate the
transcription factor cAMP-response element binding protein (CREB), which is typically involved in neurotrophic signalling in sympathetic neurons. This is the first study to identify signalling pathways activated by NTN in adult parasympathetic neurons. Our results may lead to a better understanding of regenerative mechanisms in parasympathetic neurons, especially for those innervating urogenital organs. Our results also indicate that neurotrophic signalling in parasympathetic neurons is different from that in other types of peripheral neurons.