Morphology and ultrastructure of the sympathetic celiac ganglion neurons projecting to the cardia and pylorus of the rat stomach

The stomach receives sympathetic projections from the celiac ganglion. To determine what kinds of neurons in the celiac ganglion project to the cardia or the pylorus of the stomach, we injected the retrograde tracer Fluoro-Gold into the cardia and the retrograde tracer cholera toxin subunit b into the pylorus of the same animal. A few neurons (about 10%) innervating the cardia sent collateral projections to the pylorus. Ultrastructural observations revealed that the celiac ganglion contained oval, medium-sized to large neurons. They had a dark cytoplasm containing numerous free ribosomes, rough endoplasmic reticulum, mitochondria, lysosomes, several Golgi apparatuses, and an oval nucleus. The axon terminals were small and usually contacted thin processes extending from the dendrites or the soma. About half of the terminals contained round vesicles, while the rest contained pleomorphic vesicles. Both types of terminals made asymmetric synaptic contacts. We then retrogradely labeled the neurons projecting to the cardia and the pylorus with wheat germ agglutinin conjugated horseradish peroxidase to examine their ultrastructural characteristics. The neurons projecting to the cardia (33.3 × 22.4 μm) were similar to the neurons projecting to the pylorus (33.4 × 24.7 μm) in their size and ultrastructural appearance. The neurons not projecting to the stomach (40.4 × 28.0 μm) were significantly larger than the neurons projecting to the cardia or the pylorus. Only a few axosomatic terminals were found on the neurons projecting to the cardia (1.6 per somatic profile), the pylorus (1.3) or the neurons not projecting to the stomach (0.9). These results provide morphological bases for the sympathetic motor neurons innervating the stomach.