Journal of Neuroscience, Vol 15, 1556-1566, Copyright © 1995 by Society for Neuroscience
Target regulation of a motor neuron-specific epitope
EW Chen, S Loera and AY Chiu
Division of Neurosciences, Beckman Research Institute, City of Hope, Duarte, California 91010.
In the adult rat nervous system, motor neurons are recognized specifically
by a monoclonal antibody, MO-1. Because binding by MO-1 is lost following
axotomy, contact with the target may regulate this motor neuron-specific
epitope. To test this hypothesis, we examined the recovery of MO-1
immunoreactivity in hypoglossal neurons following unilateral damage to the
hypoglossal nerve. During the first week following nerve crush, neurons in
the ipsilateral hypoglossal nucleus lost all immunoreactivity for MO-1.
Antibody binding returned with time, and by 4 weeks, 80% of the injured
neurons had recovered the MO-1 epitope. Since motor neurons reinnervate
their original targets readily following nerve crush, it appears that MO-1
binding is recovered when motor neurons return to their original target
muscles in the tongue. When the hypoglossal nerve was cut and inserted into
a foreign muscle nearby (the sternomastoid muscle), the MO-1 epitope was
not detected in the injured neurons, even when examined 6 weeks after
surgery. However, if the sternomastoid muscle was denervated prior to
insertion of the hypoglossal nerve, thus allowing the hypoglossal nerve to
synapse with this foreign target, increasing numbers of hypoglossal neurons
reacquired MO-1 immunoreactivity with time. Our results suggest that the
MO-1 epitope is only expressed in motor neurons that are in synaptic
contact with skeletal muscle. Thus, a property that distinguishes mature
motor neurons from other neuronal phenotypes appears to be regulated by
direct synaptic interaction with the postsynaptic target.