AJP - Regulatory, Integrative and Comparative Physiology, Vol 262, Issue 5 813-R818, Copyright © 1992 by American Physiological Society
Immunity to nerve growth factor and the effect on motor unit reinnervation in the rabbit
D. I. Finkelstein, A. R. Luff and J. A. Schuijers
Department of Physiology, Monash University, Clayton, Victoria, Australia.
The trophic effects of nerve growth factor (NGF) on sympathetic, peripheral
afferent, and other neural crest-derived cells have been intensively
investigated. More recently, NGF has been shown to have an influence on
motoneurons. This study was undertaken to investigate whether NGF had any
influence on the mechanical or histological properties of reinnervated
motor units. Three groups of rabbits were used: normal rabbits, rabbits in
which the nerve to medial gastrocnemius (MG) was cut and allowed to
reinnervate for 56 days, and rabbits in which the MG nerve reinnervated in
the presence of immunity to NGF. Immunity to NGF did not affect the ability
of motor axons to reinnervate a muscle, nor were the contractile
characteristics of the motor units altered. The size of horseradish
peroxidase-labeled motoneurons was not influenced by immunization against
NGF; however, the distribution of afferent neuron sizes was altered.
Conduction velocity of motor axons proximal to the neuroma was
significantly faster after immunization against NGF. Transection and
subsequent reinnervation by a peripheral nerve normally causes an increase
in myelin thickness proximal to the neuroma. However, immunization against
NGF appeared to decrease the magnitude of myelin thickening. It was
concluded that immunization against NGF affects motor axonal conduction
velocity via an influence on the neural crest-derived Schwann cells.
