Effect of nerve growth factor on intramuscular axons of neonatal mice

Newborn mice were given daily injections of nerve growth factor over the gluteus muscle. At age 9 days muscles were removed and stained to reveal intramuscular axons. Motor axons, and sensory axons of the Golgi tendon organs and muscle spindles were unaffected by nerve growth factor, but there was prolific growth of the small diameter axons that ramify over the surface of the muscle. These axons were sensory rather than sympathetic, since the degenerated following dorsal root ganglionectomy but not following sympathetic ganglionectomy. This finding supports the concept that nerve growth factor is involved in the development of sensory innervation of muscle.