Muscle derived motoneuron trophic factors promote the survival of motoneurons in vitro only when serum is present in the growth medium.

Motoneuron cultures were established from E6 chick spinal cord. Motoneurons survived for less than 2 days in chemically defined medium. The addition of muscle extract to the medium supported the survival of only a small portion (approximately 2%) of motoneurons for 8 days in vitro. A similar low survival rate was observed when the growth medium was supplemented with serum. The addition of muscle extract to serum containing medium resulted in the survival of about 20% of the motoneurons for 8 days. No differences were seen in the ability of tissue extracts prepared from E8 hindlimb, or muscle obtained from E11, E15, E18 and P3 chicks to support motoneuron survival in the presence of serum. It is apparent that although there are trophic factors present in muscle that support motoneuron survival in vitro, the actions of such trophic factors are dependent upon the presence of yet other factors found in serum.