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We present an in vitro bioassay protocol for the detailed examination of mitogenic influences on purified mouse Schwann cells. This involves measurements of (i) increases in Schwann cell number per culture, (ii) incorporation of radiolabeled thymidine per culture, and (iii) the proportion of total Schwann cells that exhibit a labeled nucleus by autoradiography. Using this standard protocol we show that the mitogenic efforts of fetal calf serum must be distinguished from its effects on cell retention to the culture substratum, and preparations of mouse brain or pituitary fibroblast growth factor but not mouse epidermal growth factor are very potent mouse Schwann cell mitogens. These mitogenic effects of serum and fibroblast growth factor have not been reported for rat Schwann cells.

Neuronal maintenance and neuritic growth during development are increasingly recognized as being under the extrinsic control of neuronotrophic- and neurite-promoting agents. Protein agents ('factors') are the most studied but not the only molecules exerting such controls. It appears increasingly likely that adult neurons in situ are equally subject to similar extrinsic regulations. Two recently studied in vivo models for peripheral and central neural regeneration have demonstrated trauma-related accumulations of neuronotrophic- and neurite-promoting factors in the adult rat, in close temporal correlation with neuronal maintenance and axonal regrowth, respectively. Deficits in the supply or utilization of similar factors may underlie neuronal or glial regressive processes in aging, and in selected neuronal diseases such as Parkinson, ALS and Alzheimer. Speculative approaches to, and potential problems of, clinical interventions addressing putative neuronotrophic deficits are discussed.