Regional specialisations of innervation and musculature of the rat stomach

The region of the gastric lesser curvature is reported to differ from other parts of the stomach in lacking rhythmic muscle movement in its proximal part, by fewer enteric nerve cells being present and by differences in distributions of interstitial cells of Cajal (ICC). Because detailed documentation of differences is lacking, we made a thorough investigation of the lesser curvature region. A substantial part of the lesser curvature region had a sparse ganglionated myenteric plexus (about 25% of the density of occurrence of ganglia in other regions). This overlapped with an area lacking longitudinal muscle, in which the enteric ganglia were serosal, at the circular muscle surface. The serosal ganglia lacked associated ICC, unlike other parts of the corpus and antrum, but ICC were numerous in the circular muscle. Close to the oesophagus, enteric ganglia were additionally between the circular and oblique muscle. Immunohistochemical investigation and muscle intracellular recording indicated that there was effective circular muscle innervation throughout the lesser curvature region, although a site of lower effectiveness of inhibitory innervation was found in the proximal part of the lesser curvature region. There was a gradient of reducing excitatory fibre innervation density towards the lesser curvature. Excitatory effects on the muscle were deduced to be indirect, as they are in the adjacent antrum. MRI of gastric movements in vivo revealed large amplitude propulsive waves of contraction at the lesser curvature towards the pylorus, and substantially, fourfold, lower amplitudes closer to the base of the oesophagus. We also describe that the major arterial supplies to the rat stomach radiate from the lesser curvature region and that mucosal specialisation does not correspond with functional or anatomical divisions of the stomach at the lesser curvature or elsewhere. Running parallel and lateral to the line of the lesser curvature were the previously reported esophago-pyloric ligaments that dynamic MRI suggested contract and relax during active antral movements. Thus, there are specialised features that distinguish the region of the lesser curvature from other gastric regions. At the proximal part of the lesser curvature, longitudinal muscle is absent, ganglia are sparse, ICC associated with ganglia are largely absent, and rhythmic circular muscle contractions have substantially lower amplitudes than more distally (in the 5 mm adjacent to the pylorus). The reduced amplitudes of contraction during peristalsis may be protective against mechanical force on the arteries and nerves that enter the stomach at the proximal lesser curvature region.