A Study of the Alimentary Canal of the Brachyopterygian FishPolypterus senegaluswith Electron Microscopy and Immunohistochemistry

Light and scanning electron microscope examination of the digestive tract in peppered moray eel, Gymnothorax pictus (Elopomorpha)

The morphology of the digestive tract of the peppered moray eel, Gymnothorax pictus (G. pictus) (Elopomorpha: Anguilliformes) was examined using both light and scanning electron microscopy. The digestive tract is composed of the esophagus, the stomach, and the intestines; pyloric caeca were absent. The stomach was divided into a cardiac region that was continuous with the esophagus, a body which terminated in a long blind sac, and a pyloric region that was continuous with the intestine. The short intestine possessed several partitions that were created by the mucosal folds within the posterior region. The terminal region of the stomach was characterized by the thick longitudinal muscularis and subserosa, and the gastric glands and microvilli were absent. Ciliary tufts of ciliated cells were observed on the surface of the partition-like mucosal folds within the intestinal wall. Acidic mucus was secreted throughout the digestive tract. It was suggested that the terminal region of the stomach is specialized for storage of large food items. In addition, it is possible that the partition-like mucosal folds within the intestine perform a function similar to that of the spiral valve and, and along with ciliated cells, facilitated digestion and absorption. The acidic mucus likely maintained surface epithelium pH and protease activity. Within a phylogenetic context, the absence of a pyloric caeca in G. pictus while possessing an intestine implies that this species is affiliated to groups that had branched off earlier than basal teleosts. Inc.

Autonomic control of gut motility: a comparative view

Gut motility is regulated to optimize food transport and processing. The autonomic innervation of the gut generally includes extrinsic cranial and spinal autonomic nerves. It also comprises the nerves contained entirely within the gut wall, i.e. the enteric nervous system. The extrinsic and enteric nervous control follows a similar pattern throughout the vertebrate groups. However, differences are common and may occur between groups and families as well as between closely related species. In this review, we give an overview of the distribution and effects of common neurotransmitters in the vertebrate gut. While the focus is on birds, reptiles, amphibians and fish, mammalian data are included to form the background for comparisons. While some transmitters, like acetylcholine and nitric oxide, show similar distribution patterns and effects in most species investigated, the role of others is more varying. The significance for these differences is not yet fully understood, emphasizing the need for continued comparative studies of autonomic control.

Ontogeny of serotonin-immunoreactive cells in the gut epithelium of the cloudy dogfish, Scyliorhinus torazame, with reference to coexistence of serotonin and neuropeptide Y

The ontogeny of serotonin (5-HT)-immunoreactive (IR) cells in the gut epithelium of an oviparous elasmobranch, Scyliorhinus torazame, was examined immunohistochemically. 5-HT-IR cells first appeared in the proximal part of the vitellointestinal duct (VID) and in the anterior part of the midgut of the embryo (30 mm in total length). At the 40-mm stage, the cells slightly increased in number and spread to the posterior part of the midgut, but no labeled cells were found in the foregut or hindgut. By the late embryonic (74- and 80-mm) stages, 5-HT-IR cells were markedly increased in number in the spiral intestine and stomach, whereas they were few in the VID and rectum. During these stages, the density of the cells in the inner yolk sac, the derivative of the VID, tended to be increased. This tendency seemed to be consistent in the posthatching juveniles at the 95-mm stage. In juveniles, 125 mm in length and 1.7 months after hatching, the cells further increased in number in the spiral intestine, reaching their adult value. Double immunostaining by the use of anti-5-HT and -neuropeptide Y (NPY) antisera demonstrated that some of the 5-HT-IR cells were also positive for NPY.