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

Effects of Bioactive Peptides from Atlantic Salmon Processing By-Products on Oxyntopeptic and Enteroendocrine Cells of the Gastric Mucosa of European Seabass and Gilthead Seabream

The present study was designed to evaluate the effects of dietary levels of bioactive peptides (BPs) derived from salmon processing by-products on the presence and distribution of peptic cells (oxyntopeptic cells, OPs) and enteric endocrine cells (EECs) that contain GHR, NPY and SOM in the gastric mucosa of European seabass and gilthead seabream. In this study, 27 seabass and 27 seabreams were divided into three experimental groups: a control group (CTR) fed a control diet and two groups fed different levels of BP to replace fishmeal: 5% BP (BP5%) and 10% BP (BP10%). The stomach of each fish was sampled and processed for immunohistochemistry. Some SOM, NPY and GHR-IR cells exhibited alternating "open type" and "closed type" EECs morphologies. The BP10% group (16.8 ± 7.5) showed an increase in the number of NPY-IR cells compared to CTR (CTR 8.5 ± 4.8) and BP5% (BP10% vs. CTR p ≤ 0.01; BP10% vs. BP5% p ≤ 0.05) in the seabream gastric mucosa. In addition, in seabream gastric tissue, SOM-IR cells in the BP 10% diet (16.8 ± 3.5) were different from those in CTR (12.5 ± 5) (CTR vs. BP 10% p ≤ 0.05) and BP 5% (12.9 ± 2.5) (BP 5% vs. BP 10% p ≤ 0.01). EEC SOM-IR cells increased at 10% BP (5.3 ± 0.7) compared to 5% BP (4.4 ± 0.8) (5% BP vs. 10% BP p ≤ 0.05) in seabass. The results obtained may provide a good basis for a better understanding of the potential of salmon BPs as feed ingredients for seabass and seabream.

Morphology, Histology, and Histochemistry of the Digestive Tract of the Marbled Flounder Pseudopleuronectes yokohamae

This study investigated the morphological, histological, and histochemical characteristics of the digestive tract of the marbled flounder (Pseudopleuronectes yokohamae). The relative length of the gut of the marbled flounder digestive tract was 1.54 ± 0.10 (n = 20), and it had a simple stomach and 6-9 pyloric caeca. The mucosal folds of the marbled flounder digestive tract exhibited a general branched morphology. The thickness and mucosal fold length of the intestinal muscularis externa showed similar aspects in all areas. The thickness of the intestinal muscularis externa was the thickest in the posterior intestine portion, and the length of mucosal folds was the longest in the anterior intestine portion. It was indicated that food digested by gastric acid in the stomach moves to the anterior portion (including pyloric caeca) and mid portion of the intestine, ensuring effective stimulation of cholecystokinin (CCK)-producing cells. In addition, the distribution pattern of CCK-producing cells in the intestine was very similar to that of mucus-secreting goblet cells. The CCK-producing cells and goblet cells in the marbled flounder were well-adapted to promote optimal control of the digestive process. Based on the morphological and histochemical studies, it was concluded that the marbled flounder displays a digestive tract comparable to that of fish species with carnivorous habits.

The Opioid System in Rainbow Trout Telencephalon Is Probably Involved in the Hedonic Regulation of Food Intake

We hypothesize that opioids are involved in the regulation of food intake in fish through homeostatic and hedonic mechanisms. Therefore, we evaluated in rainbow trout (Oncorhynchus mykiss) hypothalamus and telencephalon changes in precursors, endogenous ligands and receptors of the opioid system under different situations aimed to induce changes in the homeostatic (through fasted/fed/refed fish) and hedonic (through feeding fish a control or a palatable high-fat diet) regulation of food intake. No major changes occurred in parameters assessed related with the nutritional condition of fish (fasted/fed/refed), allowing us to suggest that the opioid system seems not to have an important role in the homeostatic regulation of food intake in rainbow trout. The responses observed in telencephalon of rainbow trout fed the palatable high-fat diet included a decrease in mRNA abundance of the opioid precursor penka, in a way similar to that known in mammals, and increased mRNA abundance of the opioid receptors oprd1 and oprk1 supporting a role for telencephalic opioid system in the hedonic regulation of food intake in fish.

Distribution of goblet and endocrine cells in the intestine: A comparative study in Amazonian freshwater Tambaqui and hybrid catfish

Goblet cells (GCs) and endocrine cells (ECs) play an important role in intestine physiology, and few studies currently exist for Amazonian fishes. This study aimed to quantify the distribution of GCs and ECs producing cholecystokinin-8 and neuropeptide Y, assessed by mucin histochemistry and peptides immunohistochemistry, in the intestine of two Amazonian species with different feeding habits Tambaqui (Colossosoma macropomum) and hybrid catfish (Pseudoplatystoma reticulatum × Leiarius marmoratus), an omnivore and carnivore, respectively. A systematic literature review correlating feeding habit and GC and EC distribution was also included to contribute to the comparative study. The results of this study provided novel information about the gut cells of Tambaqui and hybrid catfish. Both, GCs and ECs can be found sweeping the entire intestine of Tambaqui and hybrid catfish although the cells can be more concentrated in certain segments. The GCs and ECs in Tambaqui were more uniformly distributed in the midgut segments (T1, T2, and T3). Unlike, in hybrid catfish GCs were more concentrated in the hindgut (C4) and ECs mainly in the two midgut segments (C1 and C2) of hybrid catfish. Based on the comparison between Tambaqui, hybrid catfish, and other fishes in the literature review, we suggest that cell distribution can be partially explained by feeding habits, carnivorous vs. omnivorous.

Neurochemical characterization of myenteric neurons in the juvenile gilthead sea bream (Sparus aurata) intestine

We evaluated the chemical coding of the myenteric plexus in the proximal and distal intestine of gilthead sea bream (Sparus aurata), which represents one of the most farmed fish in the Mediterranean area. The presence of nitric oxide (NO), acetylcholine (ACh), serotonin (5-HT), calcitonin-gene-related peptide (CGRP), substance P (SP) and vasoactive intestinal peptide (VIP) containing neurons, was investigated in intestinal whole mount preparations of the longitudinal muscle with attached the myenteric plexus (LMMP) by means of immunohistochemical fluorescence staining. The main excitatory and inhibitory neurochemicals identified in intestinal smooth muscle were ACh, SP, 5HT, and NO, VIP, CGRP. Some neurons displayed morphological features of ascending and descending interneurons and of putative sensory neurons. The expression of these pathways in the two intestinal regions is largely superimposable, although some differences emerged, which may be relevant to the morphological properties of each region. The most important variances are the higher neuronal density and soma size in the proximal intestine, which may depend on the volume of the target tissue. Since in the fish gut the submucosal plexus is less developed, myenteric neurons substantially innervate also the submucosal and epithelial layers, which display a major thickness and surface in the proximal intestine. In addition, myenteric neurons containing ACh and SP, which mainly represent excitatory motor neurons and interneurons innervating the smooth muscle were more numerous in the distal intestine, possibly to sustain motility in the thicker smooth muscle coat. Overall, this study expands our knowledge of the intrinsic innervation that regulates intestinal secretion, absorption and motility in gilthead sea bream and provides useful background information for rational design of functional feeds aimed at improving fish gut health.

Role of calcitonin gene-related peptide in energy metabolism

PURPOSE

Calcitonin gene-related peptide (CGRP) is a neuropeptide produced by alternative tissue-specific splicing of the primary transcript of the CALC genes. CGRP is widely distributed in the central and peripheral nervous system, as well as in several organs and tissues. The presence of CGRP in the liver and brown and white adipose tissue suggests an effect of this neuropeptide on regulation of energy homeostasis.

METHODS

In this review, we summarize the current knowledge of the effect of CGRP on the control of energy metabolism, primarily focusing on food intake, thermoregulation and lipid metabolism in adipose tissue, liver and muscle.

RESULTS

CGRP induces anorexia, stimulating anorexigenic neuropeptide and/or inhibiting orexigenic neuropeptide expression, through cAMP/PKA pathway activation. CGRP also induces energy expenditure, increasing the skin temperature and brown adipose tissue thermogenesis. It has been also suggested that information related to peripheral lipid stores may be conveyed to the brain via CGRP-sensory innervation from adipose tissue. More recently, it was demonstrated that mice lacking αCGRP are protected from obesity induced by high-fat diet and that CGRP regulates the content of lipid in liver, muscle and adipose tissue.

CONCLUSIONS

It is unclear the receptor responsible by CGRP effects, as well as whether this neuropeptide acts directly or indirectly in liver, muscle and adipose tissue.

Endocrine cells producing peptide hormones in the intestine of Nile tilapia: distribution and effects of feeding and fasting on the cell density

Endocrine cells (ECs) act as a luminal surveillance system responding to either the presence or absence of food in the gut through the secretion of peptide hormones. The aim of this study was to analyze the effects of feeding and fasting on the EC peptide-specific distribution along the intestine of Nile tilapia. We assessed the density of ECs producing gastrin (GAS), cholecystokinin-8 (CCK-8), neuropeptide Y (NPY), and calcitonin gene-related peptide (CGRP) in nine segments of the intestine using immunohistochemistry. Our results show that ECs immunoreactive to CCK-8, GAS, NPY, and CGRP can be found along all the intestinal segments sampled, from the midgut to hindgut, although differences in their distribution along the gut were observed. Regarding nutrient status, we found that the anterior segments of the midgut seem to be the main site responding to luminal changes in Nile tilapia. The NPY+ and CGRP+ EC densities increased in the fasted group, while the amount of CCK-8+ ECs were higher in the fed group. No effects of fasting or feeding were found in the GAS+ EC densities. Changes in ECs density were found only at the anterior segments of the intestine which may be due to the correlation between vagus nerve anatomy, EC location, and peptide turnover. Lastly, ECs may need to be considered an active cell subpopulation that may adapt and respond to different nutrient status as stimuli. Due to the complexity of the enteroendocrine system and its importance in fish nutrition, much remains to be elucidated and it deserves closer attention.

Histochemical and immunohistochemical study on endocrine cells (5HT, GAS, and SST) of the gastrointestinal tract of a teleost, the characin Astyanax bimaculatus

Endocrine cells secrete hormones through the mucosa of the gastrointestinal tract (GIT) and act on the overall regulation of digestive processes such as nutrient absorption, gut motility and intestinal blood flow. This study aimed to determine regional distribution and frequency of endocrine cells secretory of serotonin (5-HT), somatostatin (SST) and gastrin (GAS) in the GIT of a small-bodied widespread characin Astyanax bimaculatus using histological, histochemical and immunohistochemical techniques. Fragments of the stomach and gut fixed for 8h in Bouin liquid were subjected to histological processing and immunohistochemical routine. For the histological analyses, the technique of staining with hematoxylin and eosin (HE) was used, whereas for the histochemical analyses Gomori's trichrome, periodic acid+Schiff (PAS) and Alcian blue pH 2.5 (AB) were used to further immunohistochemical processing. The stomach has a mucosa lined with a simple columnar epithelium with mucus-secreting cells; the glandular region (proximal and distal portions) has folds and pits, whereas the non-glandular region has pits only. The intestinal epithelium is simple with plain cylindrical grooved and goblet cells. The anterior region has thin folds with few goblet cells, and the posterior region with thick folds and many goblet cells. The regional distribution and frequency of endocrine cells varied across regions of the GIT with the stomach showing the highest amount of immunoreactive (IR) cells. Only the 5-HT was found in the stomach (epithelia and glands) and gut regions, with comparatively higher frequency in the stomach. SST-IR cells were found in the stomach (epithelia and gastric glands) with higher frequency in the glandular region, whereas GAS-IR were found in the gastric glands only. The stomach was the only organ to have all the three types of endocrine cells, indicating that this organ is the main site of digestion of food in this species.

Relative distribution of gastrin-, CCK-8-, NPY- and CGRP-immunoreactive cells in the digestive tract of dorado (Salminus brasiliensis)

The endocrine cells (ECs) of the gastrointestinal mucosa form the largest endocrine system in the body, not only in terms of cell numbers but also in terms of the different produced substances. Data describing the association between the relative distributions of the peptide-specific ECs in relation to feeding habits can be useful tools that enable the creation of a general expected pattern of EC distribution. We aimed to investigate the distribution of ECs immunoreactive for the peptides gastrin (GAS), cholecystokinin (CCK-8), neuropeptide Y (NPY), and calcitonin gene-related peptide (CGRP) in different segments of the digestive tract of carnivorous fish dorado (Salminus brasiliensis) by using immunohistochemistry procedures. The distribution of endocrine cells immunoreactive for gastrin (GAS), cholecystokinin (CCK-8), neuropeptide Y (NPY), and calcitonin gene-related peptide (CGRP) in digestive tract of dorado S. brasiliensis was examined by immunohistochemistry. The results describe the association between the distribution of the peptide-specific endocrine cells and feeding habits in different carnivorous fish. The largest number of endocrine cells immunoreactive for GAS, CCK-8, and CGRP were found in the pyloric stomach region and the pyloric caeca. However, NPY-immunoreactive endocrine cells were markedly restricted to the midgut. The distribution pattern of endocrine cells identified in S. brasiliensis is similar to that found in other carnivorous fishes.

Immunohistochemical study on localization of serotonin immunoreactive cells in the gastrointestinal tract of the European catfish (Silurus glanis, L.)

In this study, it was aimed to identify the distribution of serotonin immunoreactive cells within the gastrointestinal tract (GIT) of European catfish (Silurus glanis). For this purpose, the tissue samples were taken from the stomach (cardia, fundus and pylorus region) and intestine (anterior, middle and posterior region). They were examined by applying the avidin-biotin-immunoperoxidase method. The serotonin containing immunoreactive cells are presented in all regions of the GIT. It was determined to be localized generally in different distribution within the stomachs and intestines of S. glanis. It was found that the most intensive regions of immunoreactive cells were the cardia stomach and posterior of intestine.

Effects of sex and season in haematological parameters and cellular composition of spleen and head kidney of pejerrey (Odontesthes bonariensis)

Phylogenetic diversity in fish determines high interspecific variability in morphology as well as in physiological parameters. Moreover, several haematological variables and the organ composition of haemolymphopoietic sites may vary according to sex or season. The aim of this study was to establish the haematological parameters and the cellular composition of haemolymphopoietic organs in Odontesthes bonariensis, a commercially valuable fish species in Argentina, and also to determine gender or seasonal variations. Haematocrit exhibited the highest value in summer, while haemoglobin concentration was greater in summer and autumn. Erythrocyte count was higher in spring than autumn and winter, but did not differ with summer. The increase in these variables in seasons with higher water temperatures might be a compensatory mechanism to compensate the lower level of oxygen in the environment. Leucocyte formula and blast haemolymphopoietic cells in spleen and head kidney also showed annual variations since cells related to specific immune response, i.e., lymphocytes and thrombocytes, decrease in winter, whereas cells of the non-specific immune pathways, such as granulocyte, rise. The elevation of a particular type of circulating leucocyte was preceded by an increase in values of its precursor in blood in the previous season. Both, spleen and head kidney were active in haemolymphopoiesis, although with some differences in their activity during different seasons. Males showed higher values of circulating lymphoblasts and granulocytes than females, whereas females exhibited higher values of thrombocytes. This study corroborates the high interspecific variations in haematological parameters in fish that underlines the needing of basic studies in order to assess fish health status in new promising species for aquaculture.

Expression of neuropeptides and anoctamin 1 in the embryonic and adult zebrafish intestine, revealing neuronal subpopulations and ICC-like cells

This immunohistochemical study in zebrafish aims to extend the neurochemical characterization of enteric neuronal subpopulations and to validate a marker for identification of interstitial cells of Cajal (ICC). The expression of neuropeptides and anoctamin 1 (Ano1), a selective ICC marker in mammals, was analyzed in both embryonic and adult intestine. Neuropeptides were present from 3 days postfertilization (dpf). At 3 dpf, galanin-positive nerve fibers were found in the proximal intestine, while calcitonin gene-related peptide (CGRP)- and substance P-expressing fibers appeared in the distal intestine. At 5 dpf, immunoreactive fibers were present along the entire intestinal length, indicating a well-developed peptidergic innervation at the onset of feeding. In the adult intestine, vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating peptide (PACAP), galanin, CGRP and substance P were detected in nerve fibers. Colchicine pretreatment enhanced only VIP and PACAP immunoreactivity. VIP and PACAP were coexpressed in enteric neurons. Colocalization stainings revealed three neuronal subpopulations expressing VIP and PACAP: a nitrergic noncholinergic subpopulation, a serotonergic subpopulation and a subpopulation expressing no other markers. Ano1-immunostaining revealed a 3-dimensional network in the adult intestine containing multipolar cells at the myenteric plexus and bipolar cells interspersed between circular smooth muscle cells. Ano1 immunoreactivity first appeared at 3 dpf, indicative of the onset of proliferation of ICC-like cells. It is shown that the Ano1 antiserum is a selective marker of ICC-like cells in the zebrafish intestine. Finally, it is hypothesized that ICC-like cells mediate the spontaneous regular activity of the embryonic intestine.

Immunohistochemical study of the digestive tract of Oligosarcus hepsetus

AIM: To describe the histology of the digestive tract and to investigate the occurrence of endocrine cells in Oligosarcus hepsetus (O. hepsetus).

METHODS: The digestive tract (DT) of O. hepsetus was divided into esophagus, two stomach regions (glandular and non-glandular) and two intestinal regions (anterior and posterior). These specimens were processed by routine histological techniques and stained with hematoxylin-eosin, Gomori’s trichrome, periodic acid Schiff (PAS) and Alcian blue (AB). An immunohistochemical method using avidin-biotin-peroxidase was employed.

RESULTS: The esophagus is lined with a non-keratinized stratified squamous epithelium that is reactive to PAS and AB. The stomach has a mucosa lined with a simple columnar epithelium with mucus-secreting cells that are reactive only to PAS. The intestine has a simple columnar epithelium with a brush border and goblet cells that are reactive to PAS and AB. Somatostatin, serotonin and cholecystokinin immunoreactive cells were identified throughout the DT.

CONCLUSION: This study revealed adaptations for the species’ diet and showed that the distribution and relative frequency of immunoreactive cells are similar to those of other fish.

Endogenous opiates and behavior: 2011

This paper is the thirty-fourth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2011 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration (Section 16); and immunological responses (Section 17).

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.