THE DEVELOPMENT OF THE AUTONOMIC NERVOUS SYSTEM

Abstract

SummaryEarly workers have found that the peripheral sympathetic neurons arise from mesoderm, neural crest, or neural tube. In recent years various studies on normal embryos have supported each of these contradictory views. Experimental studies have yielded results which indicate an origin from the neural crest or neural tube. We feel that a neural crest origin is most probable in the light of present information.Experimental observations on the chromaffin cells of the suprarenal gland and the abdominal aortic bodies show that these cells have an origin in common with the sympathetic rudiments.The ciliary ganglion, one of the parasympathetic group, can arise independently of the semilunar ganglion. Some evidence indicates an origin for the ciliary ganglion from the neural tube, although most studies on normal embryos indicate at least a partial origin from the semilunar ganglion. Understanding of the sources of the other cranial autonomic ganglia has not been advanced in recent years.Enteric and other visceral ganglia may arise from one or more rudiments. Recent reports indicate as sources: (1) neural crest of the trunk, (2) neural crest or tube from levels of the parasympathetic nuclei in the brain stem and sacral level of the spinal cord. In addition, local differentiation from mesoderm and endoderm has been reported.Observations upon dependent differentiation of the autonomic nerves and ganglia have been made. A formative action of preganglionic fibres upon differentiation of autonomic ganglia has been suggested. Sympathetic ganglia, however, form in the absence of these fibres. The late differentiation of the ciliary ganglion depends upon the condition of its field of distribution.The following stages in the development of the sympathetic ganglia are suggested: (1) formation of the neural crest, (2) migration of crest cells, (3) differentiation of neuroblasts, (4) their incorporation into ganglia. It is presumed for this analysis that the neuroblasts arise from cells of the neural crest. At present methods of analysis are available which could serve to solve some of the problems indicate