Anatomical, histological and immunohistochemical study of the tongue in the rainbow trout (Oncorhynchus mykiss)

Macroscopic, microscopic, and immunofluorescent characterization of the Greek tortoise (Testudo graeca graeca) oropharyngeal floor with concern to its feed adaptation as a herbivorous land reptile

The current investigation focuses on gross anatomy, light, and scanning electron microscopy (SEM) of the Testudo graeca oropharyngeal floor, with particular reference to the immunofluorescence technique to examine its tongue. The T. graeca oropharyngeal floor showed many anatomical structures: the lower rhamphotheca, paralingual ridge, lower alveolar ridge, tongue, laryngeal mound, and glottis. The lower rhamphotheca appeared as a V-shaped jaw line with a highly serrated edge and a median tomium (beak). SEM observations of the lingual apex and the lingual body showed rectangular and conical filiform papillae with porous surfaces and taste pores. Meanwhile, the lingual root had two wings that carried papillae with different shapes: dagger-shaped, conical, bifurcated, and leaf-like papillae, and these papillae lacked taste pores. The laryngeal mound had openings for the laryngeal mucus gland and its secretions. Light microscopy findings showed mucous glands in the propria submucosa and near the mucosal surface of the lingual apex. The lingual root had lingual papillae and two hyaline cartilaginous skeletons between skeletal muscles, and the lingual papillae were elongated filiform, rectangular filiform papillae, and fungiform papillae. The lamina propria constituted the core of the lingual papillae and the mucous gland, they had a positive reaction with the periodic acid schiff (PAS) reagent. The apical surface of the fungiform papillae had taste pores. Under immunofluorescence, the vimentin was detected in taste bud cells, and synaptophysin reacted to the taste buds and nerve bundles. The current study of the Greek tortoise oropharyngeal floor investigated its herbivorous eating habits using its serrated lower rhamphotheca, a large tongue with differently shaped papillae, and numerous mucous glands. RESEARCH HIGHLIGHTS: The Greek tortoise (T. graeca graeca) oropharyngeal floor showed many anatomical structures: lower rhamphotheca, paralingual ridge, lower alveolar ridge, tongue, laryngeal mound, and glottis. SEM and light microscopy observations of the tongue revealed varied types and shapes of lingual papillae with a porous surface on the tongue apex (rectangular or conical filiform papillae), on the tongue body (filiform and fungiform papillae), and on the tongue root (dagger-shaped, conical, bifurcated, and leaf-like papillae). Light microscopy findings: the lamina propria constituted the core of the lingual papillae and had numerous mucous glands that had a slightly magenta-red color with PAS reagent. The apical surface of the fungiform papillae had taste pores. Vimentin and synaptophysin gave a reaction to the taste buds.

Long-term regulation of fat sensing in rainbow trout (Oncorhynchus mykiss) fed a vegetable diet from the first feeding: focus on free fatty acid receptors and their signalling

Taste plays a fundamental role in an animal’s ability to detect nutrients and transmits key dietary information to the brain, which is crucial for its growth and survival. Providing alternative terrestrial ingredients early in feeding influences the growth of rainbow trout (RT, Oncorhynchus mykiss). Thus, the present study aimed to assess the influence, via long-term feeding (from the first feeding to 8 months), of alternative plant ingredients (V diet for vegetable diet v. C diet for a control diet) in RT on the mechanism of fat sensing at the gustatory level. After the feeding trial, we studied the pathways of the fat-sensing mechanism in tongue tissue and the integrated response in the brain. To this end, we analysed the expression pattern of free fatty acid receptors (ffar) 1 and 2, markers of calcium-signalling pathways (phospholipase Cβ, Orai, Stim or Serca), the serotonin level (a key neurotransmitter in taste buds) and the expression pattern of appetite-regulating neuropeptides in the hypothalamus (central area of appetite regulation). The results revealed that the V diet modified the expression pattern of ffar1 and paralogs of ffar2 genes in tongue tissue, along with differential regulation of calcium-signalling pathways and a defect in serotonin level and brain turnover, without influencing neuropeptide expression. This study is the first to support that changes in feeding behaviour of RT fed a V diet could be due to the difference in nutrient sensing and a decrease in hedonic sensation. We revealed that RT have similar fat-detection mechanisms as mammals.

Gill arch and raker morphology of common carp (Cyprinus carpio, Linnaeus, 1758) sampled in aquaculture system

The study aimed to investigate the morphologic aspects of common carp's gill arch and gill rakers (Cyprinus carpio, Linnaeus, 1758), an omnivore and highest-produced aquaculture species. The study used 10 common carp (395.35 ± 45.06 g) grown entirely under aquaculture conditions. The fish tissues were fixed with Glutaraldehyde (2.5%) for scanning electron microscopy and with formalin (10%) for stereomicroscopic examination. In the SEM examination, two types of taste papillae (Type II and Type III) were observed in the pharyngeal mucosa. Microridge-like structures in the epithelial layer were found to have two forms. The study findings indicate a significant decrease in gill arch lengths from cranial to caudal and a significant increase in rakers per unit area, as determined through digital calliper measurements and stereomicroscopic examinations (p < 0.05). However, there was no significant difference in measurements of gill arches and raker numbers between the bilateral symmetry of the gill arches (p > 0.05). In conclusion, it was observed that the epithelial structure on the common carp gill arch contained two types of microridge-like structures: the gill arch length decreased from cranial to caudal, and the rake density on these arches increased caudally.

Anatomical oropharyngeal cavity specialisations in the cutlassfish (Trichiurus lepturus, Linnaeus, 1758)

Trichiurus lepturus is a carnivorous fish, and most of the previous anatomical research has focused on computed tomography imaging and histology of their teeth and fangs, while the remaining structures of pharyngeal cavity remain unexplored. The present research is the first to use anatomical examinations alongside scanning electron microscopy to investigate the T. lepturus oral cavity. The oropharyngeal roof included teeth, upper lip, rostral and caudal velum and the palate. The middle of the palate showed a median groove flanked by two folds, followed by a median band flanked by micro-folds, thereafter the palate became crescent shaped. The lateral regions of the palate exhibited longitudinal folds that extended rostrally towards the fangs. The oropharyngeal floor had two cavities which acted as a scabbard for the premaxillary fangs and upper velum, while the caudal sublingual cavity contained two oyster-shaped structures on the outer surface plus sublingual ridges and sublingual clefts. The tongue apex exhibited a spoon-like shape, its body demonstrated a median elevation and the root with two lateral branches contained only dome-shaped papillae. Taste buds were located on the upper velum, lower lip and the caudal part of the interbranchial septum. Images and descriptions of T. lepturus tooth structure are also provided. The present research, using anatomical dissection and morphological observation using scanning electron microscopy, has identified the structures of the dentition system, a variety in shapes of the folds and microridges, and identified the taste buds and mucous pores in the T. lepturus oropharyngeal cavity.

Vimentin Localization in the Zebrafish Oral Cavity: A Potential Role in Taste Buds Regeneration

The morphology of the oral cavity of fish is related to their feeding habits. In this context, taste buds are studied for their ability to catch chemical stimuli and their cell renewal capacity. Vimentin RV202 is a protein employed as a marker for mesenchymal cells that can differentiate along different lineages and to self-renew, while Calretinin N-18 is employed as a marker of sensory cells, and ubiquitin is a protein crucial for guiding the fate of stem cells throughout development. In this study, a surface morphology investigation and an immunohistochemical analysis have been conducted. The results of the present study reveal, for the first time, the presence of Vimentin RV202 in a taste bud cell population of zebrafish. Some taste bud cells are just Vimentin RV202-immunoreactive, while in other cells Vimentin RV202 and Calretinin N-18 colocalize. Some taste buds are just reactive to Calretinin N-18. Vimentin RV202-immunoreactive cells have been observed in the connective layer and in the basal portion of the taste buds. The immunoreactivity of ubiquitin was restricted to sensory cells. Further studies are needed to elucidate the role of Vimentin RV202 in the maturation of taste bud cells, its potential involvement in the regeneration of these chemosensory organs, and its eventual synergic work with ubiquitin.

Effects of heavy pollution in different water bodies on male rainbow trout (Oncorhynchus mykiss) reproductive health

This research aimed to investigate the influence of heavy metals on the reproductive health of rainbow trout (Oncorhynchus mykiss) captured from two locations, Verinag (S1) and Panzath (S2). Sixty (n. 60) mature rainbow trout samples (30 from each site) with body weights ranging from 400 to 650 g were collected from Verinag hatchery, which was less polluted (S1), and Panzath hatchery, which was more polluted (S2). The findings revealed significant differences between the two sites, S1 (less polluted) and S2 (more polluted), as well as significant variations within the tissues. Iron (Fe) and Zinc (Zn) were found to be highest in sampling water as well as in fish tissues sampled from S2 sites. Similarly, concerning S1 captured fishes, histopathological examination of testes from S2 captured fish was found. Testicular abnormalities that included disorganization of the seminiferous tubules, reduction in the number of germ cells (sperm cells, spermatozoa), vacuolization, and large empty areas in the seminiferous epithelium were found. In testicular cells, the frequency of apoptotic cells collected from S2 water increased significantly (P < 0.05). SOD, catalase, and glutathione peroxidase activity increased in S1 captured fishes but decreased in S2 captured fishes. MDA levels gradually increased in S2 captured fish, and the degree of heavy metal stress was positively correlated (P < 0.05). In male rainbow trout, testosterone and 11-ketotestosterone levels increased substantially in S1 captured fishes. While the fatty acids of testes in S2 fishes decreased with respect to S1 fishes. In conclusion, S2 captured fish suffered more damage due to heavy metals including cellular damage, apoptosis, oxidative damage, and altered steroid hormones when compared to fish from S1 waters.

Histological and immunohistochemical study of gilthead seabream tongue from the early stage of development: TRPV4 potential roles

BACKGROUND

Taste buds, the morphofunctional units for taste perception, transduce gustatory stimuli using G protein-coupled receptors, and a complex arrangement of ion channels, among which TRPV4, a member of the TRP superfamily. Studies on taste buds development on gilthead seabream are unknown, and the TRPV4 expression on fish taste cells studies were conducted only on zebrafish.

METHODS

In our study, we have investigated the histological features of the gilthead seabream tongue dorsal surface from the earliest stage of development using Masson trichrome with aniline blue staining. Additionally, TRPV4 expression pattern was studied by means of immunohistochemical labeling and quantitative RT-PCR.

RESULTS

We have recorded for the first time on gilthead seabream lingual dorsal surface the presence of, stage specific, three types of taste buds: type I, type II and type III in larvae, juvenile and adults respectively. At 40 days post hatching, taste buds were mature-looking. TRPV4 expression was detected in a subpopulation of taste cells of larvae, juveniles, and adults. Furthermore, TRPV4 was expressed in the basal epithelial cells of the tongue at the larvae and juvenile stage, while this expression pattern was more diffused within all the epithelial cell layers on the adult.

CONCLUSION

Our findings presume a taste sensory role of TRPV4 in the three stage-specific taste buds and oral epithelia of gilthead seabream. In addition to its sensory role on the epithelial cell layers, we hypothesize that TRPV4 is implicated in epithelial cells differentiation and membrane protection.

The Alimentary Tract of African Bony-Tongue, Heterotis niloticus (Cuvier, 1829): Morphology Study

Simple Summary

Heterotis niloticus is a primitive freshwater teleost. It is a candidate for aquaculture in Africa with a good conversion rate and is used for evolutionary studies for its anatomical similarities with reptiles and birds. H. niloticus is also an endangered species for several reasons, including overexploitation. The purpose of the present study was to investigate, by gross anatomy and light microscope analysis, the morphological structure of the digestive system of the African bony-tongue, from the oropharyngeal cavity to the rectum, including its associated glands. A peculiar feature of this species is the presence of both bone trabeculae and well-defined cartilaginous areas in the process of ossification, in the deeper layers of the tongue. The so-called “African bony- tongue” is due to these characteristics. On both sides of the tongue, two tubular structures covered by numerous taste buds, as well as mucous cells, were found. The presence of well-defined lymphoid tissue in both pyloric ceca and rectum is described for the first time. Further investigations could aim to optimize husbandry and feeding protocols permitting, also, to understand the evolutionary process.

Abstract

A morphological study of the alimentary tract, from the oropharyngeal cavity to the rectum, including the attached glands, of African bony-tongue, Heterotis niloticus (Cuvier, 1829) was carried out by gross anatomy, and light microscope analysis. This study aimed to give a deeper knowledge of the alimentary tract morphological features of this species of commercial interest. H. niloticus is distinguished by individual morphological characteristics showing a digestive tract similar to that of reptiles and birds. Within the oropharyngeal cavity, two tubular structures with digitiform ends are arranged on both lateral sides of the triangular tongue. The oropharyngeal cavity connects the stomach by a short esophagus. This latter is adapted to mechanical trituration, and it is divided into a pars glandularis and a thick-walled pars muscularis. The gizzard flows into the anterior intestine and two blind pyloric appendages, which exhibit specific functions, including immune defense for the presence of secondary lymphoid organs. The anterior intestine continues with the middle and posterior tracts up into the rectum. According to the histological observations, all regions of the alimentary tract have common structural features, typical of hollow organs, with differences in the mucosa structure that reflects the different functions of the apparatus, from mouth to anus. Within this study, we provided the first basis for future studies on optimizing rearing conditions, feed conversion ratio, and the digestive capacity, improving the growth performance of this species, and ensuring its conservation.

Morphology of the tongue dorsal surface of turbot (Scophthalmus maximus)

This study aimed to analyze the morphology of the tongue, which varies among fish species and has not been studied in turbot (Scophthalmus maximus), using macro-anatomical, light and scanning electron microscopy (SEM). As research materials, the tongues of eight adult turbot, which were used for consumption, were examined. The roughly triangular-shaped tongue of the turbot consisted of three parts: apex, body, and root. The thickness of the tongue continued to increase from the apex to the root. Although papillae were not observed in the macroscopic examination of the tongue, microscopic examination revealed the presence of cone-like shaped papillae on the submucosa. The tongue was composed of mucosa, submucosa, and hyaline cartilage. By SEM the presence of the taste buds (Types I and III), taste pores and papillae on the dorsal surface were demonstrated. Taste buds are the first descriptions in S. maximus. Therefore our results could add new data to the fish tongue anatomy.

Morphological characteristics of the blackspot seabream (Pagellus bogaraveo) tongue: A structural and immunohistochemical study

The blackspot seabream (Pagellus bogaraveo, Brünnich, 1768) is an omnivorous, predominantly carnivorous fish. In aquaculture, it is fed with pellets rich in proteins and fat. The morphological and functional aspects of the fish tongue, the feeding modality and the tasting capacity are strictly related. Therefore, the aim of this study was to describe by scanning electron, light and confocal laser microscopy, the morphological characteristics of the tongue in this species. It showed an apex, a body and a root. There were rows of teeth on the edges of the mouth and taste pores on all the tongue dorsal surface with folds and furrows. In addition, body and root showed several fungiform-like papillae in the mucosa of the folds, covered by a weakly keratinized stratified squamous epithelium, can be observed. The papillae were innervated by S100 positive fibres. In the apex, a mesenchymal tissue with vimentin positive star-shaped stem cells was evident. The results could give a support for a wider use of the blackspot seabream as a farmed species, considering the morphological data as correlated with the potentiality of food discrimination. This provides a basis for possible applications in feeding strategies. The presence, localization and characteristics of the mesenchymal stem cells, as seen also in previous studies, could represent a further basis for future applications in clinical trials.