Effects of nerve growth factor and its antibodies on sprouting of sensory axons following spinal cord hemisection.

Axons were counted in rat dorsal roots three segments cranial and three segments caudal to a spinal hemisection done at birth. The animals were placed in three groups: (1) hemisected (HEMI), (2) hemisected and given nerve growth factor (NGF) daily (HEMI + NGF) and (3) hemisected and given antibodies to NGF daily (HEMI + anti-NGF). They were sacrificed at 1 month. In the HEMI and HEMI + NGF groups, there were 20% and 13% more unmyelinated axons, respectively, in roots of the operated side. We interpret these differences to be the result of sprouting of unmyelinated axons as a result of denervation, and exogenous NGF does not seem to affect the response. By contrast, the unmyelinated axon responses in HEMI + anti-NGF animals are different. These animals have approximately 7% more unmyelinated axons on the denervated side and 50% more axons on the normal side than in the other animals we studied. The results on the anti-NGF animals are interpreted as indicating sprouting in response to a chemical denervation caused by NGF removal and the response is more dramatic on the unoperated side.