We found a network of sensory nerve fibers in the parietal peritoneum lining the abdominal cavity in the rat (Anat. Rec. 294:1376-1742 (2011)). To observe the morphology of the whole network and the topographic organization of this nerve plexus, we applied the Sihler' s staining to whole-mount preparations of the rat abdomen, including the abdominal muscles. Using this method, hematoxylin stains the myelinated nerve fibers blue, and other tissues such as muscles and peritoneal cells, become transparent.
The trunks of the 8-13th thoracic and the 1-4 lumbar nerves distributed in the parietal peritoneum. The nerve trunks from the 10th intercostal nerves to the first lumbar nerve were seen running parallel each other, running obliquely from dorso-cranial to ventro-medial direction. The main trunks ran beneath the peritoneum and reached to the m. rectus abdominis where they divided into two branches.
From nerve trunks two to four branches ran cranially and caudally. These branches were ramified and united each other. The caudal branches of the rostral intercostal nerves often united with the cranial branches of the caudal trunk to make the dense network or plexus of nerve fibers. From this network, many nerve terminals were branched off to the peritoneal cell layer.
This dense network was observed only in the parietal peritoneum of the lateral wall of the abdomen, about 8mm lateral from the ventral midline. This dense network was not observed in other area of the abdomen covered with the parietal peritoneum, such as the caudal surface of the diaphragm, the scrotum, and the ventral medial part about 8mm from the midline, although thick bundles or trunks of myelinated nerve fibers were exited there.