Ouabain binding to preimplantation rabbit blastocysts

Ciliary ganglia (CG) from 8-day-old chick embryos were cultured as explants on a highly adhesive collagen substratum in the presence of the ciliary neuronotrophic factor (CNTF). A remarkable correlation was found between the formation of an outgrowth of ganglionic nonneuronal cells and the timing and extent of neuritic development outside the ganglion. Neurites were not seen to emerge from the ganglion before the onset (24 hr after explantation) of a nonneuronal cell outgrowth. After nonneurons began to migrate over the collagen substratum, neurites could be seen to extend up to, but not beyond the distal limit of the nonneuronal outgrowth. Time-lapse analysis showed that neuritic growth cones could move in synchrony with a nonneuron with which they were in contact as well as over the nonneuronal cell surface, but not on the collagen located distally to the external edge of the nonneuronal outgrowth.Freshly dissected CGs were also grown as secondary explants on preformed host monolayers of ganglionic nonneurons. These secondary explants showed considerable neuritic development within 24 hr, while control ganglia explanted on collagen had not produced neurites. Autoradiographic experiments indicated that this neuritic outgrowth occurred on nonneuronal cells emerging precociously from the secondary explant, rather than on the preexisting host nonneurons. Electron microscopy of 24-hr explants demonstrated that, inside the ganglion, neurites were also very closely associated with the surface of nonneuronal cells.Neuritic behavior in this nonneuron/collagen terrain is compared with previously described observations of CG explants on polyornithine (PORN) or dissociated CG neurons on PORN or collagen. These observations led to the identification of a PORN-bindable neurite promoting factor (PNPF) which does not bind to, and is not active on, collagen. The hypothesis is discussed that PNPF molecules are present on the surface of nonneuronal cells and that the cells owe to those molecules their competence as a suitable terrain for the elongation of neuritic processes.