Polyornithine-attached neurite-promoting factors (PNPFs). Culture sources and responsive neurons

We have recently reported the existence within chick embryo heart cell conditioned medium (HCM) of two distinct and independently assayable factors. One agent, ciliary neuronotrophic factor (CNTF), supports the in vitro survival of 8-day chick embryo ciliary ganglionic (CG) neurons. The other factor, polyornithine-attachable neurite promoting factor (PNPF) is required for extensive neuritic growth from these same CNTF-supported CG neurons. In the present study we have examined the occurrence of PNPF activity within nearly 100 different conditioned media using our previously described chick CG bioassay system. From this screening we conclude that: (1) PNPF production is a rather widespread property of cultured neural as well as non-neural cells; and (2) the chick bioassay is sensitive to PNPF activity from all the species examined, including mouse, rat, human and chick cells. We next examined the effects of 3 representative PNPF-containing conditioned media (from chick heart, mouse Schwann and rat Schwannoma) on neurite production from 3 other peripheral ganglionic neuronal cultures (8-day chick dorsal root, 11-day chick sympathetic, and neonatal mouse dorsal root ganglia) as well as 4 central neuronal cultures (8-day chick embryo telencephalon, optic lobe and spinal cord and neonatal mouse cerebellum). The results of these studies indicate: (1) that the peripheral neurons exhibit a dramatic increase in neurite production in response to PNPF which can be easily recognized both qualitatively and quantitatively; whereas (2) the CNS neurons showed essentially no PNPF-induced increase in neurite production. The sole exception to the latter was the appearance within the chick spinal cord cultures of a neuronal population which extended very long neurites in response to PNPF.