Journal of Neuroscience, Vol 7, 3131-3141, Copyright © 1987 by Society for Neuroscience
Human muscle cultured in monolayer and cocultured with fetal rat spinal cord: importance of dorsal root ganglia for achieving successful functional innervation
T Kobayashi, V Askanas and WK Engel
Department of Neurology, University of Southern California School of Medicine, Los Angeles 90017.
Adult human muscle cultured in monolayer was cocultured with explants of
13-14-d-old rat embryo using (a) ventral spinal cord (VSC), (b) transverse
section of whole spinal cord (WSC), and (c) WSC with dorsal root ganglia
(DRG) attached (WSC + DRG). AChR clusters and AChE- positive patches, both
at the nerve-muscle contacts, were studied at 5, 12, and 21 d of coculture
with each of the 3 spinal cord preparations. In addition, AChE-positive
patches were studied after 31-64 d of coculture with WSC + DRG to evaluate
further organization of those patches. Compared to VSC and WSC cocultures,
WSC + DRG induced significantly more AChR clusters per muscle fiber at the
nerve-muscle contacts at 5 d of coculture, and the percentage of muscle
fibers containing AChR clusters was higher at all 3 time points
quantitated. The number of AChE-positive sites was the same with all 3
spinal cord preparations in early (day 5) cocultures. Between 12 and 21 d
of coculture, the number of muscle fibers containing AChE patches increased
significantly only with WSC + DRG, correlating with the increased number of
contracting muscle fibers in that coculture system. Only in human muscle
cocultured with WSC + DRG was successful innervation of the cultured muscle
fibers achieved, as manifested by (1) contractions in a continuous rhythm
of large groups of muscle fibers that were reversibly blocked by 1 mM
d-tubocurarine (aneurally cultured human muscle does not spontaneously
contract); (2) well- developed cross-striations throughout the fiber; (3)
well-organized AChE-positive sites; and (4) a trend from multifocal toward
unifocal innervation of those muscle fibers. Our studies demonstrate that
adult human muscle cultured in monolayer can be innervated by fetal rat
spinal cord and that, in our system, DRG are essential for achieving
functional innervation.