Parameters of neuritic growth from ciliary ganglion neurons in vitro: influence of laminin, schwannoma polyornithine-binding neurite promoting factor and ciliary neuronotrophic factor.

Ciliary ganglion neurons extend neuritic processes when cultured for 24 h in medium containing ciliary neuronotrophic factor (CNTF) and on a polyornithine substratum precoated with either laminin or a Schwannoma-derived neurite promoting factor (PNPF). We have examined the roles of laminin, PNPF and CNTF for each of four parameters of neuritic growth, including: initiation time, neuronal polarity, neuritic branching and average neurite output (lengths) with time. Increasing laminin and PNPF levels were found to advance the time of neurite initiation as well as shift the majority (70-80%) of the neurons from a unipolar to multipolar neuritic morphology. The polarity imposed by any given concentration of either neurite promoting factor remained constant over the 24 h culture period examined. The average lengths from the longest neurites per neuron over a 10-28 h culture interval were not affected by increasing levels of laminin or PNPF, but total neuritic output per neuron was increased. This increased total neuritic output could be attributed to a combination of earlier neuritic initiation time and an increased neuronal polarity at high laminin or PNPF levels. CNTF at threshold survival levels did not promote initiation time, neuronal polarity or total neuritic output. However, cultures receiving less CNTF than that required for maximal neuronal survival displayed an increased neuronal polarity and a reduced neuritic output before any apparent loss of neurons. Neuritic branching was not affected by either the neurite promoting or trophic factors after 24 h of culture. Laminin and PNPF were found to be indistinguishable in their effects on the ciliary ganglion neurons in each of the four parameters studied.