Neuroendocrine system of the digestive tract in Rhamdia quelen juvenile: an immunohistochemical study.

In this work, an immunohistochemical study was performed to determine the distribution and relative frequencies of some neuromodulators of the digestive tract of silver catfish (Rhamdia quelen). The digestive tract of silver catfish was divided into six portions; the oesophagus, stomach, intestine (ascendant, descendant and convoluted segments), and rectum. Immunohistochemical method using a pool of specific antisera against-gastrin, -cholecystokinin-8, -leu-enkephalin, -neuropeptide Y, -calcitonin gene-related peptide (CGRP), and -vasoactive intestinal peptide (VIP) was employed. Immunoreactivity to all antisera was identified in neuroendocrine cells (NECs) localized in the gut epithelium, although no reaction was observed in the oesophagus or stomach. The morphology of NECs immunopositive to each antibody was similar. They were slender in shape, with basally located nucleus, and their main axis perpendicular to the basement membrane. The number of NECs immunoreactive to all antisera was higher in the ascendant and descendant intestine, exhibiting a decreasing trend toward distal segments of the gut. In addition, immunoreactivity to CGRP and VIP was observed in the myenteric plexus and nerve fibers distributed in the mucosal, submucosal and muscular layers. The higher number of immunopositive NECs in the ascendant and descendant intestine may indicate the primary role of these segments in the control of food intake by means of orexigenic and anorexigenic peripheral signals.

Morphology, histology and histochemistry of the digestive system of South American Catfish (Rhamdia quelen) / Morfología, histología e histoquímica del tubo digestivo del Bagre Sudamericano (Rhamdia quelen)

The purpose of the present work was the anatomical, histo logical and histochemical description oí Rhamdia quelen juvenile digestive system. Samples of gut were fixed, dehydrated and included in paraffin and then stained with haematoxylin and eosin. For the identification and differentiation of mucosubstances the preparations were treated with Periodic Acid Schiff, Alcian Blue pH 0,4 and 2,5 andPAS/AB pH 2,5. Anatomical details of the oesophagus were like a short tube with primary and secondary mucous folds. The stratified epithelium is composed of three cellular types: small cells, abundant goblet cells with acid and neutral mucosubstances (MS) and large acid cells. The stomach is J-shaped and its mucosa presents broad and deep folds in relaxing state. Histologically, the stomach shows three different regions: cardiac, fundic and pyloric region. The luminal surface of the epithelium consists of a layer of secretory columnar cells of neutral MS. Tubuloacinar glands were surrounded by connective and muscular smooth fibers bundle. The intestine extends from the stomach until the anus, and four different sections can be distinguished: ascending, descending, convoluta and terminal straight. It was identified a simple columnar epithelium mainly composed by two cellular types: absorptive cell and goblet cell neutral MS secretory. On the basis of the anatomical and histo logical study carried out, we conclude that R. quelen presents an alimentary canal compatible with species that possess omnivorous nutritious habits.

El propósito del presente trabajo fue realizar las descripciones anatómica, histológica e histoqufmica del sistema digestivo de Rhamdia quelen jóvenes. Las muestras de intestino fueron fijadas, deshidratadas e incluidas en parafina y posteriormente teñidas con hematoxilina y eosina. Para la identificación y diferenciación de muco substancias los preparados fueron tratados con ácido periódico de Schiff, Azul Alcian pH 0,4 y 2,5 y PAS/AB pH 2,5. Los detalles anatómicos del esófago mostraron un pequeño tubo con pliegues mucosos primarios y secundarios. El epitelio estratificado presentaba tres tipos celulares: células pequeñas, abundantes células caliciformes con muco substancia (MS) acida y neutra y células grandes acidas. El estómago tenía forma de J y su mucosa presenta pliegues amplios y profundos en estado de relajación. Histológicamente, el estómago mostraba tres diferentes regiones: cardiaca, fúndica y pilórica. La superficie luminal del epitelio constaba de una capa de células columnares secretoras de MS neutro. Glándulas tubuloacinares estaban rodeadas por tejido conjuntivo y fibras musculares lisas. El intestino se extendía desde el estómago hasta el ano, y cuatro diferentes secciones era posible distinguir: ascendente, descendente, convoluta y terminal recta. Se identificó un epitelio columnar simple, compuesto principalmente por dos tipos celulares: células de absorción y células caliciformes secretoras de MS neutra. Sobre la base de los estudios anatómico e histológico realizados, se concluye que R. quelen presenta un canal alimentario compatible con las especies que poseen hábitos nutritivos omnívoros.