Journal of Neuroscience, Vol 7, 1031-1036, Copyright © 1987 by Society for Neuroscience
Accuracy of reinnervation of rat internal intercostal muscles by their own segmental nerves
VJ Hardman and MC Brown
The positions of internal intercostal motoneurons within their motor pool
were studied, following reinnervation of the intercostal muscles by their
original nerves. Six to 9 weeks after proximal nerve section in 10-d-old
and adult rats, 0.1 microliter injections of wheat germ agglutinin
(WGA)-HRP were made in the distal part of the reinnervated internal
intercostal muscle. The corresponding region of the contralateral control
muscle was also injected. The positions of the retrogradely labeled
motoneurons were mapped in 100 microns transverse sections of thoracic
spinal cord that had been stained for HRP according to the method of
Mesulam (1982). In normal rats, motoneurons innervating distal muscle
fibers are found largely in the more dorsal part of the internal
intercostal motoneuron pool (Hardman and Brown, 1985). In adult rats,
regenerated motor axons did not show any selectivity; distal muscle fibers
were innervated by motoneurons whose cell bodies were distributed
throughout the internal intercostal pool. However, in rats operated on at
10 d of age, distal intercostal muscle fibers were reinnervated by
motoneurons that were distributed mainly in the dorsal part of the motor
pool. These results support the view that positional signals may be of
importance in organizing the distribution of axon terminals within muscles
during development.