Confocal imaging and phylogenetic considerations of the subcutaneous neurons in the Atlantic hagfishMyxine glutinosa

Detecting Intestinal Goblet Cells of the Broadgilled Hagfish Eptatretus cirrhatus (Forster, 1801): A Confocal Microscopy Evaluation

Simple Summary

The intestinal epithelium of fish, similar to mammals, consists mainly of enterocytes and goblet cells. Goblet cells play a key role in the secretion of mucus, which, in addition to promoting the digestion of nutrients, is the first protective barrier against bacteria, viruses, and pathogens. Our study aims to evaluate the presence, localization, and co-localization of 5-HT, TLR2, iNOS, and Piscidin1 in goblet cells of the intestine of Eptatretus cirrhatus. The results obtained by confocal microscopy show, for the first time, the positivity of goblet cells to the antibodies tested, suggesting the involvement of these cells in the intestinal immunity of broadgilled hagfish.

Abstract

The fish intestine operates as a complicated interface between the organism and the environment, providing biological and mechanical protections as a result of a viscous layer of mucus released by goblet cells, which serves as a barrier against bacteria, viruses, and other pathogens, and contributes to the functions of the immune system. Therefore, goblet cells have a role in preserving the health of the body by secreting mucus and acting as sentinels. The ancient jawless fish broadgilled hagfish (Eptatretus cirrhatus, Forster, 1801) has a very basic digestive system because it lacks a stomach. By examining the presence, localization, and co-localization of 5-HT, TLR2, iNOS, and Piscidin1, this study intends to provide insight into the potential immune system contributions arranged by the gut goblet cells of broadgilled hagfish. Our results characterize intestinal goblet cells of broadgilled hagfish, for the first time, with the former antibodies, suggesting the hypothesis of conservation of the roles played by these cells also in primitive vertebrates. Moreover, this study deepens the knowledge about the still little-known immune system of hagfish.

Ependymal and Neural Stem Cells of Adult Molly Fish (Poecilia sphenops, Valenciennes, 1846) Brain: Histomorphometry, Immunohistochemical, and Ultrastructural Studies

This study was conducted on 16 adult specimens of molly fish (Poecilia sphenops) to investigate ependymal cells (ECs) and their role in neurogenesis using ultrastructural examination and immunohistochemistry. The ECs lined the ventral and lateral surfaces of the optic ventricle and their processes extended through the tectal laminae and ended at the surface of the tectum as a subpial end-foot. Two cell types of ECs were identified: cuboidal non-ciliated (5.68 ± 0.84/100 μm2) and columnar ciliated (EC3.22 ± 0.71/100 μm2). Immunohistochemical analysis revealed two types of GFAP immunoreactive cells: ECs and astrocytes. The ECs showed the expression of IL-1β, APG5, and Nfr2. Moreover, ECs showed immunostaining for myostatin, S100, and SOX9 in their cytoplasmic processes. The proliferative activity of the neighboring stem cells was also distinct. The most interesting finding in this study was the glia-neuron interaction, where the processes of ECs met the progenitor neuronal cells in the ependymal area of the ventricular wall. These cells showed bundles of intermediate filaments in their processes and basal poles and were connected by desmosomes, followed by gap junctions. Many membrane-bounded vesicles could be demonstrated on the surface of the ciliated ECs that contained neurosecretion. The abluminal and lateral cell surfaces of ECs showed pinocytotic activities with many coated vesicles, while their apical cytoplasm contained centrioles. The occurrence of stem cells in close position to the ECs, and the presence of bundles of generating axons in direct contact with these stem cells indicate the role of ECs in neurogenesis. The TEM results revealed the presence of neural stem cells in a close position to the ECs, in addition to the presence of bundles of generating axons in direct contact with these stem cells. The present study indicates the role of ECs in neurogenesis.

Confocal Characterization of Intestinal Dendritic Cells from Myxines to Teleosts

Dendritic cells (DCs) are antigen-presenting cells (APCs) that regulate the beginning of adaptive immune responses. The mechanisms of tolerance to antigens moving through the digestive tract are known to be regulated by intestinal DCs. Agnatha and Gnathostoma are descendants of a common ancestor. The Ostracoderms gave rise to Cyclostomes, whereas the Placoderms gave rise to Chondrichthyes. Sarcopterygii and Actinopterygii are two evolutionary lines of bony fishes. Brachiopterygii and Neopterygii descend from the Actinopterygii. From Neopterygii, Holostei and Teleostei evolved. Using immunohistochemistry with TLR-2, Langerin/CD207, and MHC II, this study aimed to characterize intestinal DCs, from myxines to teleosts. The findings reveal that DCs are positive for the antibodies tested, highlighting the presence of DCs and DC-like cells phylogenetically from myxines, for the first time, to teleosts. These findings may aid in improving the level of knowledge about the immune system's evolution and these sentinel cells, which are crucial to the body's defense.

Toxicological Evaluation of Acetylsalicylic Acid in Non-Target Organisms: Chronic Exposure on Mytilus galloprovincialis (Lamarck, 1819)

Pharmaceuticals are now considered to be established contaminants, and their presence in water poses a real risk not only to the marine ecosystem, as they may adversely affect non-target organisms that are exposed to them, but also indirectly to humans. This is particularly true for the model organism considered in this work, Mytilus galloprovincialis (Lamarck, 1819), a suspensivore and bioaccumulating organism that enters the human food chain. Among the most commonly used over-the-counter medicines, anti-inflammatory drugs certainly feature prominently, with acetylsalicylic acid (ASA) at the top. In this work, M. galloprovincialis specimens were exposed to two concentrations of ASA (10 and 100 μg/L) for 10 and 20 days to evaluate possible alterations in the decrease in regulatory volume (RVD) in digestive gland cells and cell viability of both these cells and hemocytes. In addition, the histopathological condition index of the gills and digestive gland was evaluated. The data obtained showed that chronic exposure to ASA did not alter the cell viability of hemocytes and digestive gland cells but alters the physiological mechanisms of volume regulation in the digestive gland and, in addition, a time-dose reaction to ASA in the gills and digestive gland showing numerous alterations such as lipofuscin deposits and hemocyte infiltration was found. These results confirm the potential toxicity to the marine biota, highlighting the necessity to deepen the knowledge regarding the link between over-the-counter pharmaceuticals and non-target organisms.

Rodlet cells in kidney of goldfish (Carassius auratus, Linnaeus 1758): A light and confocal microscopy study

Rodlet cells (RCs) have always been an enigma for scientists. RCs have been given a variety of activities over the years, including ion transport, osmoregulation, and sensory function. These cells, presumably as members of the granulocyte line, are present only in teleosts and play a role in the innate immune response. RCs are migratory cells found in a variety of organs, including skin, vascular, digestive, uropoietic, reproductive, and respiratory systems, and present distinct physical properties that make them easily recognizable in tissues and organs. The development of RCs can be divided into four stages: granular, transitional, mature, and ruptured, having different morphological characteristics. Our study aims to characterize the different stages of these cells by histomorphological and histochemical techniques. Furthermore, we characterized these cells at all stages with peroxidase and fluorescence immunohistochemical techniques using different antibodies: S100, tubulin, α-SMA, piscidin, and for the first time TLR-2. From our results, the immunoreactivity of these cells to the antibodies performed may confirm that RCs play a role in fish defense mechanisms, helping to expand the state of the art on immunology and immune cells of teleosts.

Effects of long-term exposure of Mytilus galloprovincialis to thiacloprid: A multibiomarker approach

Thiacloprid is a neonicotinoid insecticide widely exploited in agriculture and easily mobilized towards aquatic environments by atmospheric agents. However, little information about its toxicological effects on aquatic invertebrate bioindicators is available. In this study, specimens of the mussel Mytilus galloprovincialis were exposed to thiacloprid at environmental (4.5 μg L^-1) and 100 times higher than environmental (450 μg L^-1) concentrations for 20 days. Thiacloprid affected haemolymph biochemical parameters, cell viability in the digestive gland, antioxidant biomarkers and lipid peroxidation in the digestive gland and gills at environmentally relevant concentrations (4.5 μg L^-1). In addition, thiacloprid exposure caused histological damage to the digestive gland and gills. Interestingly, the pesticide was detected at levels equal to 0.14 ng g^-1 in the soft tissues of sentinels exposed for 20 days to 450 μg L^-1 thiacloprid in seawaterμ. Due to its harmful potential and cumulative effects after long-term exposure of M. galloprovincialis, thiacloprid may pose a potential risk to nontarget aquatic organisms, as well as to human health. This aspect requires further in-depth investigation.

Neuroepithelial cells (NECs) and mucous cells express a variety of neurotransmitters and neurotransmitter receptors in the gill and respiratory air-sac of the catfish Heteropneustes fossilis (Siluriformes, Heteropneustidae): a possible role in local immune defence

Heteropneustes fossilis is an air-breathing teleost inhabiting environments with very poor O₂ conditions, and so it has evolved to cope with hypoxia. In the gills and respiratory air-sac, the sites for O₂ sensing and the response to hypoxia rely on the expression of acetylcholine (Ach) acting via its nicotinic receptor (nAChR). This study examined the expression patterns of neuronal markers and some compounds in the NECs of the gills and respiratory air sac having an immunomodulatory function in mammalian lungs. Mucous cells, epithelial cells and neuroepithelial cells (NECs) were immunopositive to a variety of both neuronal markers (VAChT, nAChR, GABA-B-R1 receptor, GAD679) and the antimicrobial peptide piscidin, an evolutionary conserved humoral component of the mucosal immune system in fish. We speculate that Ach release via nAChR from mucous cells may be modulated by GABA production in the NECs and it is required for the induction of mucus production in both normoxic and hypoxic conditions. The presence of piscidin in mucous cells may act in synergy with the autocrine/paracrine signals of Ach and GABA binding to GABA B R1B receptor that may play a local immunomodulatory function in the mucous epithelia of the gills and the respiratory air sac. The potential role of the NECs in the immunobiological behaviour of the gill/air-sac is at moment a matter of speculation. The extent to which the NECs as such may participate is elusive at this stage and waits investigation.

Expression of acetylcholine, its contribution to regulation of immune function and O2 sensing and phylogenetic interpretations of the African butterfly fish Pantodon buchholzi (Osteoglossiformes, Pantodontidae)

Acetylcholine (Ach) is the main neurotransmitter in the neuronal cholinergic system and also works as a signaling molecule in non-neuronal cells and tissues. The diversity of signaling pathways mediated by Ach provides a basis for understanding the biology of the cholinergic epithelial cells and immune cells in the gill of the species studied. NECs in the gill were not found surprisingly, but specialized cells showing the morphological, histochemical and ultrastructural characteristics of eosinophils were located in the gill filaments and respiratory lamellae. Much remains unknown about the interaction between the nerves and eosinophils that modulate both the release of acetylcholine and its nicotinic and muscarinic receptors including the role of acetylcholine in the mechanisms of O₂ chemosensing. In this study we report for the first time the expression of Ach in the pavement cells of the gill lamellae in fish, the mast cells associated with eosinophils and nerve interaction for both immune cell types, in the gill of the extant butterfly fish Pantodon buchholzi. Multiple roles have been hypothesized for Ach and alpha nAChR in the gills. Among these there are the possible involvement of the pavement cells of the gill lamellae as O₂ chemosensitive cells, the interaction of Ach positive mast cells with eosinophils and interaction of eosinophils with nerve terminals. This could be related to the use of the vesicular acetylcholine transporter (VAChT) and the alpha 2 subunit of the acetylcholine nicotinic receptor (alpha 2 nAChR). These data demonstrate the presence of Ach multiple sites of neuronal and non-neuronal release and reception within the gill and its ancestral signaling that arose during the evolutionary history of this conservative fish species.

Acute effects of neonicotinoid insecticides on Mytilus galloprovincialis: A case study with the active compound thiacloprid and the commercial formulation calypso 480 SC

Pesticides can enter aquatic environments potentially affecting non-target organisms. Unfortunately, the effects of such substances are still poorly understood. This study investigated the effects of the active neonicotinoid substance thiacloprid (TH) and the commercial product Calypso 480 SC (CA) (active compound 40.4% TH) on Mytilus galloprovincialis after short-term exposure to sublethal concentrations. Mussels were tested for seven days to 0, 1, 5 and 10 mg L^-1 TH and 0, 10, 50 and 100 mg L^-1 CA. For this purpose, several parameters, such as cell viability of haemocytes and digestive cells, biochemical haemolymph features, superoxide dismutase (SOD) and catalase (CAT) enzymatic activity of gills and digestive gland, as well as histology of such tissues were analysed. The sublethal concentrations of both substances lead to abatement or completely stopping the byssal fibres creation. Biochemical analysis of haemolymph showed significant changes (P < 0.01) in electrolytes ions (Cl^-, K⁺, Na⁺, Ca²⁺, S-phosphor), lactate dehydrogenase (LDH) enzyme activity and glucose concentration following exposure to both substances. The TH-exposed mussels showed significant imbalance (P < 0.05) in CAT activity in digestive gland and gills. CA caused significant decrease (P < 0.05) in SOD activity in gills and in CAT activity in both tissues. Results of histological analyses showed severe damage in both digestive gland and gills in a time- and concentration-dependent manner. This study provides useful information about the acute toxicity of a neonicotinoid compound and a commercial insecticide on mussels. Nevertheless, considering that neonicotinoids are still widely used and that mussels are very important species for marine environment and human consumption, further researches are needed to better comprehend the potential risk posed by such compounds to aquatic non-target species.

Expression of Langerin/CD 207 and α-smooth muscle actin in ex vivo rabbit corneal keratitis model

The constant exposure of ocular surface to external environment and then to several microbial agents is often related to the pathogenesis of various inflammatory eye disorders. In the present study α-Smooth Muscle Actin (α-SMA) and Langerin CD/207 expression and function was investigated in a rabbit corneal keratitis. The inflammation was induced by the secreted form of glycoprotein B (gB1s) of HSV-1, in an ex vivo rabbit corneal model. α-SMA is often used as a marker for myofibroblasts. In this study, for the first time, we show α-SMA positive corneal epithelial cells, during HSV-1 cornea inflammation, demonstrating a crucial role in wound healing, especially during remodeling phase. Furthermore, we show the presence of Dendritic Cells Langerin CD/207 positive, located mainly in the basal epithelial layer and in corneal stroma during the inflammatory processes. Our result validating the ex vivo organotypic rabbit corneal model, for the study about pathogenesis of HSV-1 ocular infection.

Expression of Acetylcholine- and G protein coupled Muscarinic receptor in the Neuroepithelial cells (NECs) of the obligated air-breathing fish, Arapaima gigas (Arapaimatidae: Teleostei)

The air-breathing specialization has evolved idependently in vertebrates, as many different organs can perfom gas exchange. The largest obligate air-breathing fish from South America Arapaima gigas breathe air using its gas bladder, and its dependence on air breathing increases during its growth. During its development, gill morphology shows a dramatic change, remodeling with a gradual reduction of gill lamellae during the transition from water breathing to air breathing . It has been suggested that in this species the gills remain the main site of O₂ and CO₂ sensing. Consistent with this, we demonstrate for the first time the occurrence of the neuroepithelial cells (NECs) in the glottis, and in the gill filament epithelia and their distal halves. These cells contain a broader spectrum of neurotransmitters (5-HT, acetylcholine, nNOS), G-protein subunits and the muscarininic receptors that are coupled to G proteins (G-protein coupled receptors). We report also for the first time the presence of G alpha proteins coupled with muscarinic receptors on the NECs, that are thought as receptors that initiate the cardiorespiratory reflexes in aquatic vertebrates. Based on the specific orientation in the epithelia and their closest vicinity to efferent vasculatures, the gill and glottal NECs of A. gigas could be regarded as potential O₂ and CO₂ sensing receptors. However, future studies are needed to ascertain the neurophysiological characterization of these cells.

Expression of Langerin/CD207 in airways, lung and associated lymph nodes of a stranded striped dolphin (Stenella coeruleoalba)

The airways and lungs of vertebrates are an entrance way for several microbial pathogens. Cetaceans present an upper and lower respiratory anatomy that allows the rapid flow of large air volumes, which may lead to high susceptibility to respiratory infections. Mortality and stranding rate of Cetaceans increased dramatically, so wide the knowledge about the immune system and specific antibodies identifying immune cells populations, is of fundamental importance to monitor and document cetacean health. The aim of this study was to identify the localization of dendritic cells marked by Langerin/CD207 in airways, lungs and associated lymph nodes, of the striped dolphin Stenella coeruleoalba. Samples of trachea, bronchi, lungs and lung-associated lymph nodes were obtained from a stranded adult male of Stenella coeruleoalba. Our results showed abundant lymphoid aggregates (LAs) in the lung of S. ceruleoalba. Langerhans-like dendritic cells were well distributed along the epithelium and interstitium of respiratory tract and in associated lymph nodes. The present study deepens the knowledge about the cetacean's immune system and report about the exploitability of a commercial antibody (Langerin/CD207) for cetacean species.

Assessing the effects of neonicotinoid insecticide on the bivalve mollusc Mytilus galloprovincialis

In the present work, the marine invertebrate Mytilus galloprovincialis was used as model organism to evaluate the toxic effects of the neonicotinoid Calypso 480 SC (CAL) following 20 days of exposure to sub-lethal concentrations of 7.77 mg L^-1 (0.1% 96 h-LC50) and 77.70 mg L^-1 (1% 96 h-LC50), and a recovery period of 10 days in uncontaminated seawater. Results revealed that exposure to both concentrations of CAL increased significantly mortality rate in the cells of haemolymph and digestive gland, while digestive gland cells were no longer able to regulate cell volume. Exposure significantly reduced haemolymph parameters (Cl^-, Na⁺), affected the enzymatic activities of superoxide dismutase of digestive gland and catalase of gill, and caused also histopathological alterations in digestive gland and gills. Main histological damages detected in mussels were lipofuscin accumulation, focal points of necrosis, mucous overproduction and infiltrative inflammations. Interestingly, alterations persisted after the recovery period in CAL-free water, especially for haemocyte parameters (K⁺, Na⁺, Ca²⁺, lactate dehydrogenase, glucose). A slight recovery of histological conditions was detected. These findings suggested that sub-chronic exposure to the neonicotinoid insecticide caused significant alterations in both cell and tissue parameters of M. galloprovincialis. Considering the ecologically and commercially important role of mussels in coastal waters, a potential risk posed by neonicotinoids to this essential aquatic resource can be highlighted.

Intestinal immunity of dogfish Scyliorhinus canicula spiral valve: A histochemical, immunohistochemical and confocal study

The present study describes histochemical and immunohistochemical characteristics of the spiral valve and its associated lymphoid tissue (GALT) in the dogfish Scyliorhinus canicula. The mucosal surface of the spiral valve represents the first line of defense against pathogens coming from the external environment through food. Epithelial, mucus and immune cells play a key role in controlling the inflammatory response. Valve intestine of S. canicula had many folds lined by simple columnar cells and goblet cells, which later reacted positive to PAS, AB and AB-PAS, histochemical stains differentiated the different types of mucins; lectin histochemistry (PNA and WGA), detected neutral and acid mucins secreted that plays an important role in protection against invading pathogens. Integrin α5β1 was expressed in enterocytes that line the valve's folds with greater marking in the apical part of the cells. Laminin was found on the apical side of the epithelium, in fibrillar and cellular elements of the lamina propria and in the muscularis mucosa. In the spiral valve gut-associated lymphoid tissue (GALT) has been studied. For the first time, massive leucocytes aggregates were identified by confocal immunofluorescence techniques, using the following antibodies: TLR2, S100, Langerin/CD207. Our results expand knowledge about Dogfish valve intestine giving important news in understanding comparative immunology.

Mucosal immune parameters, immune and antioxidant defence related genes expression and growth performance of zebrafish (Danio rerio) fed on Gracilaria gracilis powder

In the present study zebrafish (Danio rerio) has been used as model organism to establish the effects of dietary supplementation of Gracilaria gracilis powder (GP) on mucosal and innate immune parameters, antioxidant enzymes, and growth. In order to establish these features, zebrafish were fed for eight weeks with experimental diets containing different levels of Red algae, 0.25, 0.5 and 1% of GP; also, a group was fed with control diet. At the end of the experimental period the antioxidant superoxide dismutase and catalase (SOD, CAT) genes expression, interleukin 1 beta (il-1β), 
lysozyme (LYZ), tumor necrosis factor alpha (TNF-α) for immune-related genes expression, total immunoglobulin (Ig), total protein, 
alkaline phosphatase (ALP) activity for innate immune parameters, and growth performance have been established. The GP dietary supplementation showed differences in SOD and CAT expression in zebrafish whole body respect to the control group. Non-signifcant differences were noticed among the different groups in case of TNF-α, LYZ and il-1expression (P > 0.05). The skin mucus total Ig and total protein in the group fed on 1% of GP were significantly higher respect to control group (P < 0.05). 0.25 and 0.5% of GP dietary supplementation significantly enhanced skin mucus ALP activity levels (P < 0.05). No significant differences were recorded for growth performances among groups (P > 0.05). The results obtained in the present study revealed that G. gracilis could be takes in account as fishes diet supplementation for its immune system stimulants effects.

Identification and distribution of neuronal nitric oxide synthase and neurochemical markers in the neuroepithelial cells of the gill and the skin in the giant mudskipper, Periophthalmodon schlosseri

Mudskippers are amphibious fishes living in mudflats and mangroves. These fishes hold air in their large buccopharyngeal-opercular cavities where respiratory gas exchange takes place via the gills and higher vascularized epithelium lining the cavities and also the skin epidermis. Although aerial ventilation response to changes in ambient gas concentration has been studied in mudskippers, the localization and distribution of respiratory chemoreceptors, their neurochemical coding and function as well as physiological evidence for the gill or skin as site for O₂ and CO₂ sensing are currently not known. In the present study we assessed the distribution of serotonin, acetylcholine, catecholamines and nitric oxide in the neuroepithelial cells (NECs) of the mudskipper gill and skin epithelium using immunohistochemistry and confocal microscopy. Colocalization studies showed that 5-HT is coexpressed with nNOS, Na⁺/K⁺-ATPase, TH and VAChT; nNOS is coexpressed with Na⁺/K⁺-ATPase and TH in the skin. In the gill 5-HT is coexpressed with nNOS and VAhHT and nNOS is coexpressed with Na⁺/K⁺-ATPase and TH. Acetylcholine is also expressed in chain and proximal neurons projecting to the efferent filament artery and branchial smooth muscle. The serotonergic cells c labeled with VAChT, nNOS and TH, thus indicating the presence of NEC populations and the possibility that these neurotransmitters (other than serotonin) may act as primary transmitters in the hypoxic reflex in fish gills. Immunolabeling with TH antibodies revealed that NECs in the gill and the skin are innervated by catecholaminergic nerves, thus suggesting that these cells are involved in a central control of branchial functions through their relationships with the sympathetic branchial nervous system. The Na⁺/K⁺-ATPase in mitochondria-rich cells (MRCs), which are most concentrated in the gill lamellar epithelium, is colabeled with nNOS and associated with TH nerve terminals. TH-immunopositive fine varicosities were also associated with the numerous capillaries in the skin surface and the layers of the swollen cells. Based on the often hypercapnic and hypoxic habitat of the mudskippers, these fishes may represent an attractive model for pursuing studies on O₂ and CO₂ sensing due to the air-breathing that increases the importance of acid/base regulation and the O₂-related drive including the function of gasotransmitters such as nitric oxide that has an inhibitory (regulatory) function in ionoregulation.