Comparative features of spinal neuronotrophic factors in fluids collected in vitro and in vivo.

Survival in monolayer culture of 4-day (stage 23) chick embryo lumbar spinal cord neurons can be regulated by two opposing activities. One, spinal neuronotrophic activity, promotes neuronal survival; and the other, spinal neuronotoxic activity, eliminates the neurons from the culture even when the trophic support is present at an optimal concentration. Quantitative microbioassays for each activity are presented and used to measure the relative amounts of each agent within different sources including glial, muscle, and spinal cord cell-conditioned media and fluid collected from peripheral and central nervous tissue lesions. Although both activities were present in all of the sources tested, their concentrations in the wound fluids were orders of magnitude greater than in the conditioned media. The fluid-derived trophic activities were inactivated by heat and trypsin and nondialyzable, whereas all of the conditioned media-derived trophic activities were heat- and trypsin-resistant and dialyzable.