Adult rat brain astrocytes support survival of both NGF-dependent and NGF-insensitive neurones

Abstract

The hypothesis that trophic substances are involved in the normal development and maintenance of the autonomic nervous system has gained much support from studies on the function of nerve growth factor (NGF). In vitro at least, both avian and mammalian sensory and sympathetic neurones have a requirement for NGF¹, or for similar, as yet uncharacterised, molecules from homologous non-neuronal cells², glial cells³, glioma cells⁴ or homogenates of certain tissues⁵. Although molecules other than NGF can apparently support the in vitro survival of apparently NGF-sensitive neurones^4,5, there has been no definitive evidence—excluding preliminary results with parasympathetic neurones of the ciliary ganglion^6–8—that other specific trophic factors are essential for neurones insensitive to NGF. I report here that adult rat brain astrocytes can promote the in vitro survival of not only NGF-dependent neurones, such as rat embryo superior cervical ganglion (SCG) cells, but also NGF-insensitive neurones such as the sensory neurones of the rat or chick embryo nodose ganglion (NG). The support of the NGF-dependent neurones is mediated by astrocyte-derived NGF, whereas the survival of NGF-insensitive neurones is brought about by a diffusible factor quite distinct from NGF, but as yet uncharacterised. Evidence is also presented which indicates that the astrocytes can support two distinct populations of neurones in the chick dorsal root ganglion (DRG). It is suggested that these populations represent respectively the previously described small, late-developing, medio-dorsal, NGF-dependent neurones and the early developing, large, ventro-lateral, NGF-insensitive neurones⁹.