Studies on the intrinsic nervous system of the wild rodent Calomys callosus digestive tract. II. The submucous plexus

The submucous plexus of the normal small and large intestine of Calomys callosus was studied by NADH and AChE histochemical techniques and by transmission and scanning electron microscopy. The plexus contains (X + SD) 7,488 + 293 neurons/cm2 in the duodenum, 5,611 + 836 in the jejunum, 2,741 + 360 in the ileum, 3,067 + 179 in the cecum, and 3,817 + 256 in the proximal colon. No ganglia or nerve cell bodies were seen in the esophagus, stomach, distal colon or rectum. The neurons are pear-shaped with a round or oval nucleus and the neuronal cell profile areas were larger in the large intestine than in the small intestine. Most of the neurons display intense AChE activity in the cytoplasm. AChE-positive nerve fibers are present in a primary meshwork of large nerve bundles and in a secondary meshwork of finer nerve bundles. At the ultrastructural level, the ganglia are irregular in shape and covered with fibroblast-like cells. The nucleoplasm of the neurons is finely granular with a few condensations of chromatin attached to the nuclear envelope. In the neuropil numerous varicosities filled with vesicles of different size and electron densities are seen. The pre- and post-synaptic membrane thickenings are asymmetric. Characteristic glial cells with oval nuclei and few organelles are numerous. These data provide a detailed description of this submucosal meshwork.

The myenteric plexus of the large intestine of the mouse: observations with supravital staining with methylene blue

Morphologic and morphometric studies of the myenteric plexus of the large intestine of the mouse were performed using supravital methylene blue staining. Male albino mice (70-80 days odl) were sacrificed after ether anaesthesia and the large intestine immediately removed and immersed in 0.1 per cent methylene blue solution in saline at 37 degrees Celsius and bubbled with air. After 25 minutes the intestine was rinsed and the lumen perfused with warm saline to remove the faeces. The caecum was sectioned and the colon was divided into three segments of the same length. The fragments, without opening the lumen, were mounted on slides and covered with coverglass for microscopic examination (4X and 10X objectives). At least 10 micrographs of each segment of intestine were used for the point counting method for evaluation of the surface area of the plexus (4x micrographs). For neuron count 10X micrographs were used. Neuron (pericaron0 volume and area were evaluated on 40X micrographs. The results shouwed: (a) the myenteric plexus in the large intestine of mouse is more dense in the proximal third of the colon than in the caecum and in the distal third of the colon; the number of neurons/cm2 is significantly less in caecum (24,352 + 4,807 neurons/cm2) and distal segment of the colon (6,5767 + 10,341 neurons/cm2) than in the proximal and intermediate segments (93,242 + 9,185 neurons/cm2 and 85,188 + 5154 neurons/cm2, respectively). The mean volume of the neurons was similar in the diferent segments of the colon (4549 + 3493 mum3).