Date of Award

Fall 2014

Degree Type


Degree Name

Doctor of Philosophy (PhD)



First Advisor

Terry L. Powley

Committee Chair

Terry L. Powley

Committee Member 1

Edward A. Fox

Committee Member 2

Jean-Christophe Rochet

Committee Member 3

John R. Burgess


A full description of the terminal morphology of sympathetic postganglionic axons innervating the musculature of the gastrointestinal (GI) tract has not been available. Furthermore, common assumptions about the morphology and distribution of catecholaminergic terminal fields have been strongly shaped by the limitations of the techniques employed to distinguish the fibers and complicated by inconsistent findings generated with various methodologies. Thus, the present experiment used modern neural tracer techniques to provide high-resolution labeling of sympathetic fibers projecting to the smooth muscle wall of the GI tract. Fischer 344 rats (N = 50) received injections of dextran biotin into the left celiac and superior mesenteric ganglia. Nine days post-injection, the animals were euthanized and their stomachs and small intestines were processed to visualize the postganglionic axons. Myenteric neurons were counterstained with Cuprolinic Blue. Individual sympathetic arbors (n = 154) in the gut wall were inventoried, digitized and analyzed morphometrically. After entering the GI tract wall, sympathetic axons branched extensively to form complex terminal arrays within the myenteric ganglia and adjacent tertiary plexus. Sympathetic arbors also formed long rectilinear multiply branched arrays of neurites within the circular muscle and its associated secondary plexus. A small subset (13%) of individual sympathetic axons terminated solely in the myenteric ganglia, while another minority subset (27%) exclusively innervated the secondary plexus and circular muscle. In contrast, the largest group of endings (i.e., 60%) formed heterotypic arbors that innervated the myenteric ganglia and either the tertiary plexus and/or the secondary plexus/circular muscle. Though past experiments relying on fluorescence histochemistry have emphasized sympathetic axons projecting to the myenteric plexus, and thus apparently controlling smooth muscle function indirectly through these enteric ganglion projections, the fact that some 87% of sympathetic axons project extensively, or even exclusively, to the smooth muscle sheets is consistent with the view that sympathetic postganglionic axons are organized to control smooth muscle directly.