In vivo survival requirement of a subset of nodose ganglion neurons for nerve growth factor

The sensory neurons of the nodose ganglion are the classic example of a pop ulation of peripheral nervous system neurons that do not require nerve grow th factor (NGF) for survival during development but are dependent on other neurotrophins. We have re-examined this assertion by studying the developme nt of the nodose ganglion of mice that have a null mutation in the NGF gene . Compared with wild-type embryos, the number of neurons undergoing apoptos is was elevated in NGF(-/-) mice, resulting in a significant reduction in t he total number of neurons in the ganglion by the end of embryonic developm ent. TrkA, the NGF receptor tyrosine kinase, was expressed in the nodose ga nglion throughout development and there was a marked decrease in TrkA mRNA expression in the nodose ganglion of NGF(-/-) embryos. Although the in vitr o survival of the majority of nodose neurons was promoted by brain-derived neurotrophic factor (BDNF), a minor proportion was supported by NGF in cult ures established over a range of embryonic stages. These results clearly de monstrate that a subset of nodose ganglion neurons depends on NGF for survi val during development. The finding that the expression of tyrosine hydroxy lase (TH) mRNA was unaffected in the nodose ganglia of NGF-deficient embryo s indicates that this NGF-dependent subset is distinct from the subset of c atacholaminergic neurons in the nodose ganglion.