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.

First description of an olfactory neuroblastoma in goldfish Carassius auratus: a case report

An external pinkish growing mass that emerged from the right nostril of an adult goldfish Carassius auratus L. was evaluated by means of light microscopy and immunohistochemistry. The neoplasm presented a well-developed fibrovascular stroma associated with solid cell nests and a large number of Flexner-Wintersteiner rosettes. Myelinated fibres were observed around them. Neoplastic cells showed a prominent degree of nuclear atypia and low mitotic activity. The latter was in agreement with the low reactivity of tumour cells to anti-proliferating cell nuclear antigen antibody. Immunohistochemistry also revealed anti-neuronal nitric oxide synthase, anti-S100 protein, antineuropeptide Y, and anti-cytokeratin immunoreactivity in tumour cells as well as in normal olfactory epithelium of goldfish control sections. Histopathological and immunohistochemical findings strongly suggest a diagnosis of an olfactory neuroblastoma (ONB). To our knowledge this is the first description of ONB in goldfish.

An immunohistochemical study of the gut neuroendocrine system in juvenile pejerrey Odontesthes bonariensis (Valenciennes)

In this study, several neuropeptides were identified by immunohistochemistry in neuroendocrine cells (NEC) located in the gut epithelium and nerve cell bodies of the enteric nervous system of pejerrey Odontesthes bonariensis, a species that is a promising candidate for intensive aquaculture. The neuropeptides involved in orexigenic or anorexigenic action, i.e. gastrin, cholecystokinin-8, neuropeptide Y and calcitonin gene-related peptide (CGRP), displayed a significantly higher number of immunoreactive NECs in the anterior intestine, suggesting that this region of the gut plays an important role in the peripheral control of food intake. On the other hand, leu-enkephalin and vasoactive intestinal peptide (VIP), both associated with the modulation of the enteric immune system, showed no significant variations in the mean value of immunopositive NECs between the anterior and posterior intestine. This may indicate that their activity is required at a similar level along the entire gut. In addition, CGRP and VIP-immunoreactive neurons and nerve fibres were observed in the myenteric plexus, which might exert synergistic effects with the neuropeptides immunolocalized in NECs.

Development of rodlet cells in the gut of turbot (Psetta maxima L.): relationship between their morphology and S100 protein immunoreactivity

Rodlet cells are an enigmatic cell type described in tissues of both marine and freshwater teleosts. Although their structure is well established, up to date their function remains subject of debate. However, there is consensus among the majority of researchers that rodlet cells play an important role within immune system, and this function is probably related with the release of rodlets due to contractile capability of their fibrous layer. Regulation of the contraction mechanism would require proteins that modulate Ca(++) intracellular concentration to be expressed in rodlet cells. We performed a morphological and immunohistochemical study at light and electron microscopy levels to assess S100 protein immunoreactivity in developing rodlet cells. Immature stages did not exhibit immunoreactive signal; however, immunoreactivity was observed in the fibrous layer of both transitional and mature rodlet cells. The latter stage also showed immunosignal within the rodlets. These findings suggest a clear association between S100 protein expression and rodlet cell development that could be linked to the regulation of rodlet activity and contractile property of their fibrous layer. Furthermore, S100 protein antibody constitutes a novel marker for rodlet cells that could be used in future studies of this particular cell type.

Ultrastructural Characterization of Gills in Juveniles of the Argentinian Silverside, Odontesthes bonariensis (Valenciennes, 1835) (Teleostei: Atheriniformes)

An ultrastructural study was performed on the gills of juvenile Argentinian silverside, Odontesthes bonariensis. The gills are composed of two sets of four holobranchs and, in turn, each holobranch consists of a gill arch and two rows of caudolaterally projecting branchial filaments. From the dorsal and ventral surfaces of each filament, branchial lamellae radiate out as foldings of the epithelial layer. Gill rakers are present on each of the gill arches, on the anteromedial side of the arch opposite to the filaments. Gill rakers, gill arches and branchial filaments are covered by a stratified epithelium, whereas branchial lamellae essentially consist of a thin epithelial envelope containing capillaries. In the stratified epithelium, mucous cells, rodlet cells, granular cells, pavement epithelial cells and mitochondria-rich cells are identified. The thin epithelium that lines the lamellae comprises two cell types, outer and inner epithelial cells, and the capillary walls on the inside of the epithelial envelope are defined by pillar cells. The ultrastructure of all these cell types is described and our findings are discussed in light of the existing data on fish gill morphology. In the gills of juvenile Argentinian silverside is of particular interest the characteristics showed by mitochondria-rich cells, such as their arrangement in clusters of 2-3 cells and their small and depressed surface in contact with the aquatic milieu, features which strongly resemble those of euryhaline species.