[show abstract][hide abstract] ABSTRACT: The study provides the first comprehensive information on the immunohistochemistry and ultrastructure of the olfactory receptor neurons (ORNs) in the mudskipper, Periophthalmus barbarus. The olfactory sensory epithelium is in the form of islets which cover part of the olfactory canal running from the upper lip toward the eye, where large single accessory nasal sacs occur. Within the islets, microvillous, ciliated and crypt ORNs were observed as well as giant cells and sparse non-sensory ciliated cells. Around the islets and in the walls of accessory nasal sacs, there are epidermal cells with microridges typical of fish epidermis. Close to the entrance to the accessory nasal sac, in the non-sensory epithelium of the nasal cavity and the skin epithelium covering the olfactory organ, areas of solitary chemosensory cells (SCCs) are reported for the first time. The distribution of the various ORN cell types is assessed through the immunohistochemistry against olfactory receptor coupled G-proteins. The ciliated ORNs were labeled by G alpha olf/s antibody. The ORNs with microvilli and crypt cells were G alpha i-3 immunoreactive.
[show abstract][hide abstract] ABSTRACT: pseudobranchial neurosecretory cells in scorpion catfish Heteropneustes fossilis: an environment scanning electron microscope and transmission electron micro-scope study. — Acta Zoologica (Stockholm) 94: 58–65. Pseudobranchial neurosecretory system (PNS), found in the gill region of cer-tain groups of teleosts, falls under the category of the 'diffuse neuroendocrine system' (DNES). The cells belonging to the system share morpho-functional features with the paraneuronal cells observed in respiratory tract and airway sur-faces of higher vertebrates. On the basis of the experimental observations, a role in condition of hypoxia has been recorded for this system. In an attempt to eluci-date the ultrastructure of pseudobranchial neurosecretory cells, present investi-gation was undertaken using environment scanning electron microscope (ESEM) and TEM in an air-breathing catfish, Heteropneustes fossilis. The external morphology of PNS under ESEM appeared as a mass of cells supplied with nerves and blood capillaries. Each cell mass is made up of numerous pear-shaped neurosecretory cells, confirmed by neurosecretion-specific acid violet stain. The TEM investigation of the cells revealed the presence of different sizes of dense-cored vesicles in the cytoplasm, which was observed as granular cyto-plasm under light microscope. Presence of large number of mitochondria in the cytoplasm confirmed active involvement of these cells in the physiology of fishes. Although lacuna prevails regarding the exact function of this system of fish, its probable role in hypoxic condition and surfacing behavior are speculated.
[show abstract][hide abstract] ABSTRACT: The skin is the primary interface between the body and the environment, and has a central role in host defence. In the epidermis, Langerhans’ cells form an interconnecting network of dendritic cells, that play a central role within inflammatory and immune responses of terrestrial and aquatic mammals, but few studies aimed at their characterization have been carried out in cetaceans, so far. Toll-like receptors are crucial players in the innate immune response to microbial invaders. These receptors are expressed on immune cells, such as monocytes, macrophages, dendritic cells, and granulocytes.
The aim of this preliminary study was to describe the expression of Toll-like receptor 2 in a stranded striped dolphin (Stenella coeruleoalba) skin. Immunoreactive cells were predominantly found within the stratified squamous epithelium. Other Toll-like receptor 2 positive cells of varying morphology, were results may help to increase the knowledge on the interaction occurring between dolphins and the environment in which they live at their most crucial interface: the skin.
[show abstract][hide abstract] ABSTRACT: Swim bladders and lungs are homologous structures. Phylogenetically ancient actinopterygian fish such as Cladistians (Polypteriformes), Ginglymods (Lepisosteids) and lungfish have primitive lungs that have evolved in the Paleozoic freshwater earliest gnathostomes as an adaptation to hypoxic stress. Here we investigated the structure and the role of autonomic nerves in the physostome swim bladder of the cyprinid goldfish (Carassius auratus) and the respiratory bladder of lepisosteids: the longnose gar and the spotted gar (Lepisosteus osseus and L. oculatus) to demonstrate that these organs have different innervation patterns that are responsible for controlling different functional aspects. The goldfish swim bladder is a richly innervated organ mainly controlled by cholinergic and adrenergic innervation also involving the presence of non-adrenergic non-cholinergic (NANC) neurotransmitters (nNOS, VIP, 5-HT and SP), suggesting a simple model for the regulation of the swim bladder system. The pattern of the autonomic innervation of the trabecular muscle of the Lepisosteus respiratory bladder is basically similar to that of the tetrapod lung with overlapping of both muscle architecture and control nerve patterns. These autonomic control elements do not exist in the bladders of the two species studied since they have very different physiological roles. The ontogenetic origin of the pulmonoid swim bladder (PSB) of garfishes may help understand how the expression of these autonomic control substances in the trabecular muscle is regulated including their interaction with the corpuscular cells in the respiratory epithelium of this bimodal air-breathing fish.
[show abstract][hide abstract] ABSTRACT: Anatomical and functional studies of the autonomic innervation in the conus arteriosus of the garfishes are lacking. This study reveals that the conus arteriosus of the longnose gar is primarily myocardial in nature, but additionally, large numbers of smooth muscle cells are present in the subendocardium. A well-developed system of adrenergic, cholinergic, substance P (SP) and neuronal nitric oxide synthase (nNOS) positive nerve terminals are found in the wall of the conus arteriosus. Coronary blood vessels running in the adventitia receive a rich supply of nNOS positive nerve fibers, thus suggesting their importance in the nitrergic control of blood flow in the conus arteriosus. The present data show that the patterns of autonomic innervation of the garfish conus arteriosus are more complex than previously appreciated.
[show abstract][hide abstract] ABSTRACT: Anatomical and functional studies on the autonomic innervation as well as the location of airway receptors in the air-bladder of lepisosteids are very fragmentary. These water-breathing fishes share in common with the bichirs the presence of a glottis (not a ductus pneumaticus) opening into the esophagus. In contrast to a high concentration of neuroepithelial cells (NECs) contained in the furrowed epithelium in the lung of Polypterus, these cells are scattered as solitary cells in the glottal epithelium, and grouped to form neuroepithelial bodies (NEBs) in the mucociliated epithelium investing the main trabeculae in the air-bladder of Lepisosteus osseus and L. oculatus. The present immunohistochemical studies also demonstrated the presence of nerve fibers in the trabecular striated musculature and a possible relation to NEBs in these species, and identified immunoreactive elements of this innervation. Tyrosine hydroxylase (TH), choline acetyltransferase (ChAT), 5-HT and neuropeptide immunoreactivities were detected in the intramural nerve fibers. 5-HT and VIP immunopositive nerve fibers are apparently associated with NEBs. TH, VIP and SP immunoreactivities are also present in nerve fibers coursing in the radially arranged striated muscle surrounding the glottis and its submucosa. 5-HT positive neurons are also found in submucosal and the muscle layers of the glottis. The physiological function of the adrenergic and inhibitory innervation of the striated muscle as well as the neurochemical coding and morphology of the innervation of the NEBs are not known. Future studies are needed to provide evidence for these receptors with the capacity of chemoreceptors and/or mechanoreceptors.
[show abstract][hide abstract] ABSTRACT: Anatomical and functional studies of the autonomic innervation of the photophores of luminescent fishes are scarce. The present immunohistochemical study demonstrated the presence of nerve fibers in the luminous epithelium and lens epithelium of the photophores of the hatchet fish, Argyropelecus hemigymnus and identified the immunoreactive elements of this innervation. Phenylethanolanine N-methyltransferase (PNMT) and catecholamine (CA)-synthesizing enzymes were detected in nerve varicosities inside the two epithelia. Neuropeptides were localized in neuropeptide Y (NPY) and substance P (SP)- and its NK11 receptor-immunopositive nerves in the lens epithelium. Neuropeptides were also localized in non-neural cell types such as the lens cells, which displayed immunoreactivities for pituitary adenylate cyclase activating peptide (PACAP) and their receptors R-12 and 93093-3. This reflects the ability of the neuropeptide-containing nerves and lens cells to turn on and off the expression of selected messengers. It appears that the neuropeptide-containing nerves demonstrated in this study may be sensory. Furthermore, neuronal nitric oxide synthase-immunopositive axons associated with photocytes in the luminous epithelium have previously been described in this species. Whereas it is clear that the photophores receive efferent (motor) fibers of spinal sympathetic origin, the origin of the neuropeptide sensory innervation remains to be determined. The functional roles of the above neuropeptides or their effects on the bioluminescence or the chemical nature of the terminals, either sensory or postganglionic neurons innervating the photophores, are still not known.
[show abstract][hide abstract] ABSTRACT: Functional studies of the autonomic innervation in the photophores of luminescent fishes are scarce. The majority of studies have involved either the stimulation of isolated photophores or the modulatory effects of adrenaline-induced light emission. The fish skin is a highly complex organ that performs a wide variety of physiological processes and receives extensive nervous innervations. The latter includes autonomic nerve fibers of spinal sympathetic origin having a secretomotor function. More recent evidence indicates that neuropeptide-containing nerve fibers, such as those that express tachykinin and its NK1 receptor, neuropeptide Y, or nitric oxide, may also play an important role in the nervous control of photophores. There is no anatomical evidence that shows that nNOS positive (nitrergic) neurons form a population distinct from the secretomotor neurons with perikarya in the sympathetic ganglia. The distribution and function of the nitrergic nerves in the luminous cells, however, is less clear. It is likely that the chemical properties of the sympathetic postganglionic neurons in the ganglia of luminescent fishes are target-specific, such as observed in mammals.
[show abstract][hide abstract] ABSTRACT: The presence of mast cells has been reported in all classes of vertebrates, including many teleost fish families. The mast cells of teleosts, both morphologically and functionally, show a close similarity to the mast cells of mammals. Mast cells of teleosts, localized in the vicinity of blood vessels of the intestine, gills and skin, may play an important role in the mechanisms of inflammatory response, because they express a number of functional proteins, including piscidins, which are antimicrobical peptides that act against a broad-spectrum of pathogens. An increase in the number of mast cells in various tissues and organs of teleosts seems to be linked to a wide range of stressful conditions, such as exposure to heavy metals (cadmium, copper, lead and mercury), exposure to herbicides and parasitic infections. This study analyzed the morphological localization and abundance of mast cells in the intestine and gills of sea bream, Sparus aurata, after a 12, 24 or 72 h exposure to PCB 126, a polychlorinated biphenyl, which is a potent immunotoxic agent. In the organs of fish exposed to PCB 126, it was observed that in addition to congestion of blood vessels, there was extravasation of red blood cells, infiltration of lymphocytes, and a progressive increase in numbers of mast cells. These data confirm the immunotoxic action of PCB, and the involvement of mast cells in the inflammatory response.
[show abstract][hide abstract] ABSTRACT: The carotid labyrinth is an enigmatic endocrine structure of unknown chemosensory function lying in the gill region of the catfishes. The carotid body is found at the carotid bifurcation of amphibians and all mammalian vertebrates on the evolutionary tree. It is a vascular expansion comprised of a cluster of glomus cells with associated (afferent and efferent) innervations. In the catfish species studied (Clarias batrachus) a neurosecretory cell system consisting of pseudobranchial neurosecretory cells connect the carotid labyrinth or large vessels (both the efferent branchial artery and dorsal aorta), and is likely akin to the glomus cells, but comparing these structures in widely divergent vertebrate species, the conclusion is that the structural components are more elaborate than those of terrestrial vertebrates. However, these cells reveal both an endocrine phenotype (such as the association with capillaries and large vessels) and the presence of regulatory substances such as neurotransmitters and neuropeptides producing good evidence for high levels of conservation of these substances that are present in the glomus cells of mammalian vertebrates. VIP-immunopositive neuronal cell bodies are detected in the periphery of the carotid labyrinth. They are presumptive local neurons that differ from pseudobranchial neurosecretory cells, the latter failing to express VIP in their soma.
[show abstract][hide abstract] ABSTRACT: Zaccone, D., Grimes, A.C., Farrell, A.P., Dabrowski, K. and Marino, F. 2011. Morphology, innervation and its phylogenetic step in the heart of the longnose gar Lepisosteus Osseus. —Acta Zoologica (Stockholm) 00: 1–9.AbstractAnatomical and physiological studies of cardiovascular control in garfish are scarce. The combination of muscle labelling and neurochemical identification of extrinsic and intrinsic nerves in the heart of Lepisosteus osseus reveals a well-developed system of adrenergic, cholinergic, substance P (SP)- and neuronal nitric oxide synthase (nNOS)-containing nerve terminals in the walls of the conus arteriosus, the sinus venosus and the atrium. Double labelling showed that nNOS-immunoreactive terminals do not co-label for tyrosine hydroxylase (TH) and choline acetyl transferase (ChAt). Coronary blood vessels running in the epicardium of the conus arteriosus and ventricle receive a rich supply of nNOS-positive nerve fibres. The main intracardial localization of nervous tissue is in a sinoatrial plexus corresponding to the pacemaker region of the heart. This plexus is a network of SP-, vasoactive intestinal polypeptide (VIP)- and pituitary adenylate cyclase-activating polypeptide (PACAP)-positive nerve fibres and nerve cell bodies, but its function in fish cardiac regulation remains to be elucidated. This study provides morphological data on distinct nitrergic, peptidergic, ChAT and TH nerve terminals thus pertaining to the neurochemical content of the vagal motor and adrenergic, and intrinsic innervation revealing a complexity of the neuronal control of the garfish heart. The neurochemical features of the innervation patterns of the heart put Lepisosteus with teleosts and among the more apical actinopterygians.
[show abstract][hide abstract] ABSTRACT: This article concerns a specialized system of neurons that populate the heart – the intracardiac neurons. These neurons are distinct from the adrenergic and cholinergic neurons that reach cardiac tissues as part of the sympa thetic nervous system (see section Extrinsic Innervation and Chemical Codes of Autonomic Neurons). Intracardiac neurons recognized in the sino-atrial area suggest the possibility of the heart containing intrinsic circuits that modulate local activities.
Fishes are the most prolific vertebrate group in terms of biomass and number of species, occupying widely differing aquatic environments, which results in different lifestyles and different demands on the heart. Some fishes
even breathe air, and this has resulted in the evolution of circulatory changes as extreme as a double circulatory loop in obligate air-breathing lungfish (Dipnoi) and a partial structural division of the ventricle, by a vertical septum and an atrio-ventricular plug, into a larger right and a smaller left side (see section The Gross Morphology and Anatomy of the Heart). Consequently, these evolutionary changes are expected to have resulted in alterations in the intracardiac innervation among fishes, as is the case for the sympathetic and parasympathetic cardiac innervation patterns (see section Extrinsic Innervation and Chemical Codes of Autonomic Neurons). While the discoveries concerning intracardiac neurons are still in an early stage, certain patterns have already begun to emerge.
[show abstract][hide abstract] ABSTRACT: Immunohistochemical studies using antisera against various neuropeptides (Substance P, vasoactive intestinal polypeptide, and cholecystokinin octapeptide) and tyrosine hydroxylase revealed both olfactory sensory neuron (OSN) polymorphisms and transepithelial-subepithelial nerves in the olfactory epithelium of the cartilaginous fish, Scyliorhinus canicula. This study provides the first evidence of three morphological types of OSNs within the olfactory epithelium of cartilaginous fish that are similar to those found in the teleosts. In fishes there is evidence that OSNs differ functionally, including their differential olfactory bulb projections and molecular properties. The Substance P positive olfactory neurons in S. canicula may have a separate bulbar projection site that is not known, but may indicate a characteristic found in olfactory neuron subtypes in both lampreys and teleost fish. Numerous Substance P immunopositive nerves are found at the base of and in the olfactory epithelium. Some of them were observed to extend outwards almost reaching the epithelial surface. Their presumptive origin from the trigeminal nerve and their interrelationship with chemosensory cells in the nasal passages of vertebrates are discussed.