Neurochemical differentiation of functionally distinct populations of autonomic neurons

The coeliac ganglion of guinea pigs displays a unique topographical arrange ment of neurochemically and functionally distinct populations of sympatheti c neurons. The authors used multiple-labeling immunohistochemistry to inves tigate the neurochemical differentiation of these neurons during embryonic and fetal development. Sympathoadrenal precursors, located on either side o f the abdominal aorta, were intensely immunoreactive for tyrosine hydroxyla se (TH-IR), neurofilament, and the human natural killer 1 antibody at midem bryonic stages (Carnegie stages 16-19). During late embryonic stages (stage s 20-23), a single bilobed ganglion had formed. At this time, neuropeptide Y immunoreactivity (NPY-IR) was widely expressed in sympathetic neurons (wi th moderate TH-IR) and chromaffin cells (with intense TH-IR). The onset of somatostatin (Som-IR) expression followed that of NPY-IR and was restricted to sympathetic neurons. However, at late embryonic stages, most TH-IR neur ons with Som-IR also expressed NPY-IR (a combination of peptides not found in the mature coeliac ganglion). Between late embryonic stages and the end of the early fetal period, there was a significant increase in the proporti on of neurons in lateral regions that had both NPY-IR and TH-IR. At the sam e time, there was an increase in the proportion of neurons in medial region s that had both Som-IR and TH-LR. Neurons expressing both Som-IR and TH-IR were rarely observed in lateral regions of the coeliac ganglion. Thus, a cl ear topography within the coeliac ganglion is established during late embry onic and early fetal stages of development and reflects that found in the m ature animal by the end of the early fetal period. J. Comp. Neurol. 429:419 -435, 2001. (C) 2001 Wiley-Liss, Inc.