Alpha-gustducin-immunoreactive solitary chemosensory cells in the developing chemoreceptorial epithelium of the rat vallate papilla

The presence of solitary chemosensory cells was studied in rat vallate papillae during the first week of post-natal life by alpha-gustducin immunocytochemistry. In 1- to 3-day-old rats, isolated alpha-gustducin-immunoreactive cells were found within the epithelium of the vallate papilla. These cells, mainly located in the basal layer, were scattered among keratocytes and wrapped in alpha-gustducin-negative epithelial cells in a glia-like fashion. The alpha-gustducin-immunoreactive cells were usually round and some of them gave rise to short, large processes directed towards the lumen of the oral cavity or the basal lamina. Rarely, some cells showed an evident bipolar shape. Small taste buds containing either alpha-gustducin-immunoreactive or alpha-gustducin-negative cells appeared in the vallate papillae of 4-day-old rats in which isolated, bipolar-shaped alpha-gustducin-immunoreactive cells were also found. After the first week of post-natal life, the taste buds appeared basically similar to those of adult animals. In conclusion, the present study demonstrates that the presence of epithelial cells with characteristics of solitary chemosensory cells precedes the development of the taste buds.     

Laryngeal chemosensory clusters

The expression of molecules involved in the transductory cascade of the sense of taste (TRs, alpha-gustducin, PLCbeta2, IP3R3) has been described in lingual taste buds or in solitary chemoreceptor cells located in different organs. At the laryngeal inlet, immunocytochemical staining at the light and electron microscope levels revealed that alpha-gustducin and PLCbeta2 are mainly localized in chemosensory clusters (CCs), which are multicellular organizations differing from taste buds, being generally composed of two or three chemoreceptor cells. Compared with lingual taste buds, CCs are lower in height and smaller in diameter. In laryngeal CCs, immunocytochemistry using the two antibodies identified a similar cell type which appears rather unlike the alpha-gustducin-immunoreactive (IR) and PLCbeta2-IR cells visible in lingual taste buds. The laryngeal IR cells are shorter than the lingual ones, with poorly developed basal processes and their apical process is shorter and thicker. Some cells show a flask-like shape due to the presence of a large body and the absence of basal processes. CCs lack pores and their delimitation from the surrounding epithelium is poorly evident. The demonstration of the existence of CCs strengthens the hypothesis of a phylogenetic link between gustatory and solitary chemosensory cells.     

Evolutionary origins of taste buds: phylogenetic analysis of purinergic neurotransmission in epithelial chemosensors

Taste buds are gustatory endorgans which use an uncommon purinergic signalling system to transmit information to afferent gustatory nerve fibres. In mammals, ATP is a crucial neurotransmitter released by the taste cells to activate the afferent nerve fibres. Taste buds in mammals display a characteristic, highly specific ecto-ATPase (NTPDase2) activity, suggesting a role in inactivation of the neurotransmitter. The purpose of this study was to test whether the presence of markers of purinergic signalling characterize taste buds in anamniote vertebrates and to test whether similar purinergic systems are employed by other exteroceptive chemosensory systems. The species examined include several teleosts, elasmobranchs, lampreys and hagfish, the last of which lacks vertebrate-type taste buds. For comparison, Schreiner organs of hagfish and solitary chemosensory cells (SCCs) of teleosts, both of which are epidermal chemosensory end organs, were also examined because they might be evolutionarily related to taste buds. Ecto-ATPase activity was evident in elongate cells in all fish taste buds, including teleosts, elasmobranchs and lampreys. Neither SCCs nor Schreiner organs show specific ecto-ATPase activity, suggesting that purinergic signalling is not crucial in those systems as it is for taste buds. These findings suggest that the taste system did not originate from SCCs but arose independently in early vertebrates.     

The chemosensory anterior dorsal fin in rocklings (Gaidropsarus and Ciliata, Teleostei, Gadidae): activity, fine structure and innervation

Observations and experiments on the behaviour of shore rocklings have shown that the modified and vibratile anterior dorsal fin can be involved in the detection of food but is not essential to foraging by the fish. The epidermis of the vibratile fin rays contains numerous chemosensory cells, of similar cytology in the two species studied. These chemosensory cells are compared with the gustatory cells of the taste buds borne on other fin rays. Synaptic modifications in both cases consist of densities on the apposed membranes, with a dense layer under the membrane of the neurite more distinct than that in the cell. Vesicles are not a feature of these synapses, although some of the sensory cell bases are vesicular. Denervation experiments have shown that the chemosensory cells of the vibratile rays are supplied by a facial nerve component. After denervation a small proportion of the sensory cells were found to have an association with spinal nerve fibres. The present status of solitary chemosensory cells in fishes is discussed.     

New details of the ultrastructure (TEM, SEM) of taste buds in fishes

Quantitative distribution of the taste buds (TB) in different parts of the body and the fine structure of the TB components are described in Cobitis taenia L. No evidence of synaptic contacts between any cellular components in the TB has been found. The afferent synapses have been recognized only at the gustatory cells and at the basal cell. The microvillar processes on the upper side of the basal cell are demonstrated for the first time in fishes. These processes resemble those at the basal cells in the TB of tetrapods and at the Merkel cells, scattered in the epidermis of all vertebrates. Since the basal cells of fish TB correspond also to other criteria of the Merkel cells, its mechanoreceptive function in the TB is discussed. A relatively large number of atypical gustatory cells has been found in the studied material. As the examined specimens of C. taenia lived for a long time in aquarium conditions, it may be supposed that these gustatory cells are damaged by pollutants introduced mainly with food such as Tubifex. For purposes of comparison, a related species, Misgurnus fossilis L., was used in the study.     

Sensory structures at the surface of fish skin I. Putative chemoreceptors

Fish skin contains solitary epidermal sensory cells which, on evidence from their cytology, are believed to be chemosensory. The external appearance of the apical sensory processes of these cells, as seen by scanning electron microscopy, is shown in four species of ostariophysan teleosts, and is compared with the morphology of the pores of external taste buds. The apical processes of the gustatory cells are simple in form in all cases so far investigated in gnathostome fishes, but in some cases the solitary sensory cells have apical processes divided distally into a number of smaller processes. In the dipnoan fish Protopterus amphibius , external taste buds have simple blunt gustatory processes protruding through a cap of mucus that covers the taste bud pore. Solitary sensory cells in this species have a bulbous undivided apical process. In the lampreys, the 'end buds' have an apical morphology different from the taste bud pores of teleost fish. Lamprey epidermis has numerous solitary sensory cells each bearing a number of microvilli.     

Interdigitating cells in the thymus of the turtle Mauremys caspica

Summary Interdigitating cells are non-lymphoid elements in the thymus and peripheral, secondary lymphoid organs of higher vertebrates. Their origin and functional significance are a matter of controversy. In the present investigation we analyze, for the first time, the nature of presumptive interdigitating cells of the thymus of an ectothermic vertebrate, the turtle Mauremys caspica. This model is specially useful because of the seasonal variations that affect the reptilian lymphoid organs. Immature pro-interdigitating cells and phagocytosing mature interdigitating cells are described with special emphasis on their ultrastructural characteristics and possible relationships with monocytes and macrophages.     

The structure of the nervous system of the pluteus larva of Strongylocentrotus purpuratus

Summary Tissues that have the ultrastructural characteristics of nervous tissues are associated with ciliary and muscular elements of the pluteus larva of Strongylocentrotus purpuratus. The nerve cells are found along the margins of the ciliary bands, which are composed predominantly of spindle-shaped ciliated cells. The nerve cells contribute axonal processes to a tract of axons, which runs at the base of the ciliary band throughout its length. Axonal tracts, in the esophagus, lie beneath the circumesophageal muscles. Branched microvilli, which have been interpreted as sensory receptors, are located on the oral side of the main ciliary band and connect with the nerve cells in the ciliary band. The nervous structures described here, and other tissues of the pluteus that have been previously described as nervous, are compared on the basis of their association with receptor and effector organs, and their ultrastructural characteristics.     

Ultrastructure of the tastebuds of the red-eared turtle,Chrysemys scripta elegans

The fine structure of the turtle tastebud has been examined by light, transmission, and scanning electron microscopy. It contains five types of cells on the basis of their cytological features, designated types 1,2,3,A, and B. Types 1, 2, and 3 reach the taste pore, whereas types A and B are located basally. The type 2 cell has access to the tongue surface, i.e., the site of gustatory stimuli, and also synapses onto afferent nerves; it probably is a gustatory receptor cell and corresponds to the so-called “light” cell observed in other vertebrate tastebuds. Some cells may be differentiating. In support of this hypothesis, light microscopic autoradiography shows that postmitotic cells occur in the tastebuds within 24 hours after administration of H³-thymidine. The tastebuds of the turtle are similar to those of other vertebrates described electron-microscopically.     

T1R3 is expressed in brush cells and ghrelin-producing cells of murine stomach

Various digestive and enteroendocrine signaling processes are constantly being adapted to the chemical composition and quantity of the chyme contained in the diverse compartments of the gastrointestinal tract. The chemosensory monitoring that underlies the adaptive capacity of the gut is thought to be performed by so-called brush cells that share morphological and molecular features with gustatory sensory cells. A substantial population of brush cells is localized in the gastric mucosa. However, no chemosensory receptors have been found to be expressed in these cells so far, challenging the concept that they serve a chemosensory function. The canonical chemoreceptors for the detection of macronutrients are taste receptors belonging to the T1R family; these have been identified in several tissues in addition to the gustatory system including the small intestine. We demonstrate the expression of the T1R subtype T1R3, which is essential for the detection of both sugars and amino acids in the gustatory system, in two distinct cell populations of the gastric mucosa. One population corresponds to open-type brush cells, emphasizing the notion that they are a chemosensory cell type; T1R3 immunoreactivity in these cells is restricted to the apical cell pole, which might provide the basis for the detection of luminal macronutrient compounds. The second gastric T1R3-positive population consists of closed-type endocrine cells that produce ghrelin. This finding suggests that ghrelin-releasing cells, which lack access to the stomach lumen, might receive chemosensory input from macronutrients in the circulation via T1R3.     

Solitary chemosensory cells — taste,common chemical sense or what?

Summary Secondary solitary chemosensory cells (SCCs) occur scattered within the epidermis of lampreys, teleosts and ranid tadpoles. Counts in representative telost species revealed that SCC's outnumber chemosensory cells organized in taste buds. Therefore, SCCs may be considered the structural substrate of a basic and probably important vertebrate chemosense. However, detailed information on structure, innervation and function is only available from specialized fins in a few teleost species, where SCCs are sufficiently concentrated. The foremost research model has been the anterior dorsal fin (ADF) in rocklings, which contains millions of SCCs but no other specialized chemosensory elements. It has been shown that these ADF-SCCs are innervated from the recurrent facial nerve. Electrophysiological recordings revealed that there is virtually no overlap in stimulus spectrum between the ADF-SCCs and pelvic fin taste buds; SCC responses could only be triggered by dilutions of heterospecific fish body mucus. Results of behavioural experiments indicate that fish mucus is indeed a relevant stimulus. Therefore it is hypothesized that the biological role of the ADF-SCCs is predator avoidance rather than search for food. Whether these findings are valid for rockings only, or can be generalized for the scattered SCC systems in more than 20000 species of fish and in some amphibians, remains an open question. Further investigations on the function and biological roles of the SCC chemosense will be crucially important to improve our understanding of sensory perception and its evolution in aquatic vertebrates.     

Light,electron microscopical,and immunocytochemical investigation of the stomach wall of the tigerfish Hydrocynus forskahlii

The wall of the stomach of the tigerfish is described and compared with that of other vertebrates. Light microscopic and ultrastructural characteristics of the stomach wall correspond to a large extent to those of other vertebrates, although some differences are found. The mucosa contains (1) surface epithelium characterized by narrow columnar cells with abundant mucous granules; (2) gastric glands consisting of pepsinogenic cells of variable height, containing tubulovesicles and bearing microvilli; (3) five granulated cell types located basally in the epithelium (types 1–5); and (4) lamina propria and muscularis mucosae. Connective tissue separating smooth muscle fibers of the muscularis mucosae constitutes a stratum compactum. The submucosa contains a loose connective tissue, a tunica muscularis of inner circular and outer longitudinal layers, and a serosa of mesothelium and subjacent connective tissue. Immunocytochemical tests with antisera to five polypeptides show gastrin/cholecystokinin (CCK), vasoactive intestinal polypeptide (VIP) immunoreactivities in some cells of the gastric glands, and somatostatin in cells lying among epithelial cells lining the gastric luminal surface or gastric pits.     

The consequences of gustatory deafferentation on body mass and feeding patterns in the rat

The contribution of orosensory signals, especially taste, on body mass, and feeding and drinking patterns in the rat was examined. Gustatory deafferentation was produced by bilateral transection of the chorda tympani, glossopharyngeal, and greater superficial petrosal nerves. Total calories consumed from sweetened-milk diet and oil-chow mash by the nerve-transected rats significantly decreased relative to sham-operated controls, mostly attributable to decreases in bout number, but not size. Nevertheless, caloric intake steadily increased over the postsurgical observation period, but body mass remained below both presurgical baseline and control levels and did not significantly increase over this time. After the sweetened-milk diet/oil-chow mash phase, rats received a series of sucrose preference tests. Interestingly, the nerve-transected rats preferred sucrose, and intake did not differ from controls, likely due to the stimulus sharing some nontaste chemosensory properties with the sweetened-milk diet. The neurotomized rats initiated a greater number of sucrose-licking bouts that were smaller in size and slower in licking rate, compared with control rats, and, unlike in control rats, the latter two bout parameters did not vary across concentration. Thus, in the absence of gustatory neural input, body mass is more stable compared with the progressive trajectory of weight gain seen in intact rats, and caloric intake initially decreases but recovers. The consequences of gustatory neurotomy on processes that determine meal initiation (bout number) and meal termination (bout size) are not fixed and appear to be influenced by presurgical experience with food stimuli coupled with its nongustatory chemosensory properties.     

Characterization of relationships between pro- and eukaryotic cells under the conditions of intracellular symbiosis of Staphylococcus aureus in the mucosa cells of the respiratory and digestive systems organs in terms of ecology and morphology

The ecological and morphological analysis of reorganization processes in the cell and tissue structures of the mucous membranes of the respiratory and digestive systems in rats under the conditions of their prolonged symbiotic interactions with staphylococci (in the body of rats as a whole, as well as on the model of organotypic cultures in diffusion chambers in vivo) was carried out with the use of light and electron microscopy, radioautography and morphometry. The morphological equivalents of phenotypic reactions in the cell elements of the mucous membranes of the respiratory and digestive systems (epitheliocytes, leimyocytes, endotheliocytes, macrophages and fibroblasts) under the conditions of staphylococcus persistence were revealed. Adaptive and reactive shifts in eukaryotic cells were manifested by an increased volume of nuclei and greater proportion of euchromatin and a decreased DNA-synthetic and proliferative activity. Microorganisms located inside the cells underwent ultrastructural reorganization.     

A reexamination of the epithelial sensory cells of amphioxus (Branchiostoma)

The rostral epithelium of a newly metamorphosed juvenile of Branchiostoma floridae was examined at the EM level to confirm previous reports on its sensory cells. The majority of the sensory cells are of three types: two type I variants, with simple collars of unbranched microvilli surrounding their cilia, and one kind of type II cell, with an extended collar of repeatedly branched microvilli. The two type I variants differ in the structure and arrangement of the microvilli, basal body and rootlet, and the length of the cilium. Both variants are probably primary sensory cells (i.e. each has its own axon), but the data supporting this conclusion are much better for one variant than for the other. Type II cells are secondary sensory cells, with synaptic terminals borne on short extensions of the cell body. The presence of degenerating type II cells suggests that they may be subject to a regular process of loss and renewal. The results do not resolve the evolutionary issue of how amphioxus sensory cells relate to the epithelial sensory and receptor cells of vertebrates. Being primary, the type I cells resemble the supposed ancestral type more closely than do type II cells. Type II cells may be chemosensory, however, and should not be ruled out a priori as possible homologues of either primary or secondary chemosensory cells in vertebrates.     

Taste buds as peripheral chemosensory processors

Taste buds are peripheral chemosensory organs situated in the oral cavity. Each taste bud consists of a community of 50–100 cells that interact synaptically during gustatory stimulation. At least three distinct cell types are found in mammalian taste buds – Type I cells, Receptor (Type II) cells, and Presynaptic (Type III) cells. Type I cells appear to be glial-like cells. Receptor cells express G protein-coupled taste receptors for sweet, bitter, or umami compounds. Presynaptic cells transduce acid stimuli (sour taste). Cells that sense salt (NaCl) taste have not yet been confidently identified in terms of these cell types. During gustatory stimulation, taste bud cells secrete synaptic, autocrine, and paracrine transmitters. These transmitters include ATP, acetylcholine (ACh), serotonin (5-HT), norepinephrine (NE), and GABA. Glutamate is an efferent transmitter that stimulates Presynaptic cells to release 5-HT. This chapter discusses these transmitters, which cells release them, the postsynaptic targets for the transmitters, and how cell–cell communication shapes taste bud signaling via these transmitters.     

Immunohistochemical distribution of neuropeptide Y in the mesencephalon and rhombencephalon of carp, Cyprinus carpio L. (Cyprinidae: Teleostei)

The localization of neuropeptide Y (NPY)-immunoreactive elements was investigated in the mesencephalon and rhombencephalon of carp, Cyprinus carpio, by using antisera raised against porcine NPY and the immunoperoxidase technique. Concurrently, to identify the distribution of NPY-immunoreactivity, we developed an atlas of the studied areas based on Nissl-stained sections. The NPY-immunoreactive (NPY-ir) elements were located in many zones of the mesencephalon and rhombencephalon. In the mesencephalon, positive fibers were the most abundant elements while neurons were scarce. The rhombencephalon rostral part was characterized by a low to moderate fiber density, distributed in the ventro-medial and ventro-lateral region. Differently the caudal part of the rhombencephalon exhibited several NPY-ir elements. In particular, a high density of immunoreactivity was located in the gustatory area at the level of the nucleus (n.) originis nervi glossopharyngei, in the n. nervi vagi, and in the vagal lobe. The latter can be considered a valid neuroanatomical model for the study of gustatory signal processing in vertebrates. Our results regarding the primary gustatory centers give neuroanatomical support to the view that NPY may act as a neurotransmitter and/or a neuromodulator in a wide neural network for feeding behavior control.     

Histopathology and cell culture characteristics of liver cells from grc − and grc + rats given diethylnitrosamine

The histopathological response and cell culture characteristics of liver cells from the R16 (grc ^–) strain of rats, which carries an MHC-linked deletion, were examined one week after a single intraperitoneal injection of 200 mg/ kg body weight diethylnitrosamine (DEN) and were compared with the response of liver cells from wild type (grc+) rats. The DEN exposure induced hydropicl vacuolar changes in the parenchymal cells and a limited proliferation of oval cells in the periportal areas of the livers of both grc+ and grc rats. Primary culture of collagenase-digested livers consisted of parenchymal, bile ductular and oval-related cells as determined by cell-specific immunohistochemistry. Subpassaged cells from grc+ rats exhibited oval cell ultrastructural morphology, inducible histochemical staining for gammaglutamyl transpeptidase (GGT), and DEN-associated onset of anchorage-independent growth. Primary cultures of liver cells from R16 rats consistently failed to form cell strains upon subpassage.Abbreviations DEN diethylnitrosamine - grc growth and reproduction complex - GGT gamma-glutamyl transpeptidase - MHC major histocompatibility complex     

Solitary chemosensory cells: why do primary aquatic vertebrates need another taste system?

The taste-like system of solitary chemosensory cells (SCCs) has almost eluded scientific attention. This is particularly remarkable, since recent surveys have revealed that this system of epidermal cells is widespread and abundant among the anamniotic aquatic vertebrates. In the rocklings (Gadidae, Teleostei), high densities of SCCs occur at a specialized dorsal fin. Recent evidence from this model indicates that SCCs are narrowly tuned to dilutions of fish body mucus and bile. Thus, SCCs may sample the ambient water for the upstream presence of potential competitors or predators. However, in sea robins (Triglidae, Teleostei), SCCs seem to be involved in finding food. Information from many more species is needed to explain why SCCs and taste buds have been maintained in parallel for such a long evolutionary period of time - from the age of the agnathans to that of the most advanced teleost fishes.