Development of the spinal nerves in the mouse with special reference to innervation of the axial musculature

Abstract

Development of the mouse spinal nerves was studied. On E11 (11th day of gestation), the primitive spinal nerve fascicle extended ventrally in the anterior half of the sclerotome. Spinal nerves in the forelimb region united with each other to form the primitive brachial plexus. Their terminal segment was covered by a peculiar cell mass. On E12, five primary branches developed along the primitive spinal nerve trunk. The ramus dorsalis was originally a cutaneous nerve, supplying two series of branches to the skin of the back. The medial series was derived from the dorsal ramus of C2-C8, and the lateral series from C8 and the more caudal dorsal rami. Nerves of the former series took the presegmental course through the intermyotomic space, while those of the latter the postsegmental course. The ramus cutaneous lateralis was a nerve that took the presegmental course to become cutaneous. The ramus intercostalis externus was a muscle branch whose distribution was restricted within the segment. The ramus anterior was a muscle branch from the end of the primitive spinal nerve trunk. The ramus visceralis connected a thoracic nerve with the para-aortic sympathetic cell cord. On E13-16 the ramus anterior secondarily gave off a cutaneous branch (ramus cutaneous anterior). The ramus intercostalis externus extended ventrally deep to the intercostalis externus muscle, crossing just caudal to the ramus cutaneous lateralis that secondarily gave off branches to the obliquus externus abdominis muscle.

Developmental origins of precocial forelimbs in marsupial neonates

“…11E,F); in an adult opossum (and in mammals in general) there is no connection from C3 to the brachial plexus (Harris, 1939) (verified for M. domestica by our laboratory, data not shown). In mouse, C3 never grows towards or into the brachial plexus during embryonic development (Nakao and Ishizawa, 1994). Thus, although the anterior expansion of the forelimb bud seems to have impacted early spinal nerve growth into the limb, this is corrected as development proceeds so that in the adult a typical mammalian pattern is observed.…”

“…By stage 31, the branch from C3 into the brachial plexus is greatly diminished (F, arrow). In mouse, C3 never grows towards the brachial plexus (Nakao and Ishizawa, 1994). nt, neural tube; np, nasal pit; t, tongue muscle precursors; fl, forelimb bud; s, somite; an, accessory nerve; hn, hypoglossal nerve.…”

EphA3 Null Mutants Do Not Demonstrate Motor Axon Guidance Defects

“…We found that EphA3 is expressed in motor neurons starting at E10 of mouse embryogenesis, during which time motor axons extend into the periphery and begin to make pathway choices (32). In view of the limb bud expression of ephrin A ligands (3,14,16,33), and our own demonstration that ectopic EphA3 expression can direct retinal axon guidance decisions (2), we hypothesized that EphA3 directs axon guidance decisions in the MMC.…”

Ramification Patterns of the Nerves Innervating the Forearm Extensors in Mammals and Reptiles

“…Namely, a phylogenetically constant ramification pattern reflects muscle phylogeny. This seems to be supported by the fact that the primary and secondary branches of the intercostal nerves are at least differentiated during its development, and that the route of the secondary nerves are more unstable than that of the primary (Nakao & Ishizawa, 1994.…”