Journal of Neuroscience, Vol 5, 1208-1221, Copyright © 1985 by Society for Neuroscience
Selective reinnervation of intercostal muscles transplanted from different segmental levels to a common site
DJ Wigston and JR Sanes
We transplanted external intercostal muscles from one of several thoracic
(T) levels to the neck of adult rats. The cervical sympathetic trunk, which
innervates the superior cervical ganglion, was cut, and its proximal end
was apposed to the muscle. Preganglionic axons in the trunk reinnervated
muscle fibers in the transplants. We determined the segmental origin of
synaptic inputs to transplanted muscles by recording intracellularly from
muscle fibers while stimulating individual ventral roots which supply axons
to the trunk. In one series of experiments, T2 or T8 muscles were
transplanted from the thorax to the neck of the same rat. While T2 and T8
muscles were reinnervated to a similar extent, they differed in the
segmental origin of the innervation they received: T2 muscles received more
inputs from rostral segments (T1 and T2) than did T8 muscles, and T8
muscles received more inputs from caudal segments (T4 to T6) than did T2
muscles. This difference between reinnervation of T2 and T8 muscles was
detected both 2 to 4 weeks and 10 to 14 weeks after surgery. In a separate
series, using rats of an inbred strain, T3, T4, or T5 muscles were
transplanted from one rat to a separate host. Again, the average segmental
origin of inputs to transplants from different levels differed
systematically: it was most rostral to T3 muscles, intermediate to T4
muscles, and most caudal to T5 muscles. Finally, T3 and T5 muscles were
soaked in a myotoxin, Marcaine, before reimplantation. This treatment kills
muscle fibers but not myoblastic satellite cells; therefore, muscle fibers
were replaced by regeneration. Marcaine-treated T3 and T5 muscles were
successfully reinnervated but did not differ significantly in the segmental
origin of their inputs. Our results show that adult mammalian muscles can
be selectively reinnervated, and they raise the possibility that the
selectivity is based on some positional quality that matches axons and
muscles from corresponding segments. However, while differences among
muscles survive denervation and transplantation, their expression or
accessibility may change during regeneration.
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