Specificity of sympathetic preganglionic projections in the chick is influenced by the somitic mesoderm

It has been shown that the development of segmentally specific sympathetic preganglionic projections in the chick is influenced by the tissue environment along the pathway of the preganglionic axons. The cellular origin of this influence, however, is not known. In the present study, transplantation of quail somites into chick hosts showed that the cells in the local environment of the sympathetic trunk are derived from the somite. Surgical manipulations of chick somites then were performed to investigate whether somites play a role in the establishment of preganglionic projection patterns. When cervical somites were transplanted to the thoracic region, preganglionic neurons adjacent to the transplanted somites projected aberrantly. In addition, when somites were removed, the pattern of preganglionic axonal projections to their target ganglia was altered. These results indicate that the specificity of sympathetic preganglionic projections is influenced by the somitic mesoderm.