Abstract
Rat spinal cord cells maintained in neuron-rich cultures were exposed to extracts of skeletal muscle or to medium conditioned by non-neuronal cells. The conditioned media enhanced neuronal acetylcholine (ACh) synthesis, choline acetyltransferase activity, and protein synthesis, and decreased gamma-aminobutyric acid (GABA) synthesis. Muscle extract prepared from newborn rats produced similar enhancements but did not depress GABA synthesis. Muscle extracts prepared from normal and denervated adult rat limbs contained relatively little activity. These results suggest that different molecular factors might mediate the effects on GABA and ACh synthesis. Gel filtration of conditioned media and muscle extracts revealed that all of these activities were confined to a macromolecular fraction with an apparent Mr of 40,000. These tissue-derived factors affecting neuronal protein and transmitter synthesis are in turn distinct from a neuronal survival-promoting factor obtained from serum (Kaufman, L. M., and J. N. Barrett (1983) Science 220: 1394–1396).