title: Localization of motor neuron pools supplying identified muscles in normal and supernumerary legs of chick embryo.
abstract: Neuromuscular specificity has been investigated in chick embryos with a grafted supernumerary leg. The nerves of the lumbar plexus are divided between the two legs so that rostral nerves innervate the grafted leg and the caudal nerves supply the host's original leg. The basic topographic organization of the histologically definable motor neuron clusters of the lateral motor columns remains unchanged by the addition of a supernumerary leg. Intramuscular injections of identified leg muscles have been used to map the intraspinal location of specific motor pools in stage 38 (12-day) embryos. In the normal embryo, the gastrocnemius muscle is innervated by neurons in a central dorsal cluster of motor neurons in segments 26-29. In six experimental cases, the motor neurons supplying the gastrocnemius muscle of a rostrally placed grafted leg were consistently located in a specific medial cluster of neurons in segments 23-25. Motor neurons in this location never normally innervate a gastrocnemius muscle, even in the very young embryos during the period of naturally occurring cell death. This observation of a systematic mismatch between a particular motor cluster and an abnormally innervated muscle indicates the operation of a selective developmental process. A hierarchy of selective chemoaffinities may best explain our experimental results.
mesh_terms: D000818:Animals; D002642:Chick Embryo; D006614:Hindlimb / Q000294:innervation* / Q000637:transplantation; D009046:Motor Neurons / Q000502:physiology*; D009132:Muscles / Q000294:innervation*; D014184:Transplantation, Homologous
references.citation: Prog Brain Res. 1964;11:93-119
references.pmid: 14300484
references.citation: J Bone Joint Surg Br. 1955 Nov;37-B(4):540-58
references.pmid: 13271481
references.citation: Proc Natl Acad Sci U S A. 1963 Oct;50:703-10
references.pmid: 14077501
references.citation: Exp Neurol. 1963 Jan;7:46-64
references.pmid: 13965388
references.citation: Am J Anat. 1958 May;102(3):365-409
references.pmid: 13617221
references.citation: J Comp Neurol. 1976 Dec 1;170(3):311-20
references.pmid: 993371
references.citation: J Physiol. 1975 Jul;249(2):301-26
references.pmid: 1177095
references.citation: J Comp Neurol. 1976 May 15;167(2):143-64
references.pmid: 58875
references.citation: J Comp Neurol. 1974 Jan 1;153(1):59-76
references.pmid: 4544669
references.citation: Brain Res. 1969 Jul;14(2):245-54
references.pmid: 4893860
references.citation: Brain Res. 1975 Nov 14;98(2):291-302
references.pmid: 1182520
references.citation: J Comp Neurol. 1975 Apr 15;160(4):535-46
references.pmid: 1123466