Rat serum contains a developmentally regulated cholinergic inducing activity.

Sympathetic neurons cultured in defined medium do not develop the ability to produce acetylcholine, as do neurons grown with serum supplementation (lacovitti, L., M. I. Johnson, T. H. Joh, and R. P. Bunge (1982) Neuroscience 7:2225-2239; Wolinsky, E. J., S. C. Landis, and P. H. Patterson (1985) J. Neurosci. 5: 1497-1508). The implication that rat serum contains cholinergic inducing activity is further explored here. Dependence of cholinergic induction on serum concentration is demonstrated, and the activity is shown to reside in a macromolecular fraction. Very little cholinergic inducing activity is present in serum obtained from animals younger than 9 postnatal days. This age dependence correlates with the time of transition from noradrenergic to cholinergic transmitter status by the sympathetic innervation of the rat sweat gland in vivo (Landis, S. C., and D. Keefe (1983) Dev. Biol. 98: 349-372).