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PubMed2006

Brain and sensory organ morphology in Antarctic eelpouts (Perciformes: Zoarcidae: Lycodinae).

Eelpouts of the family Zoarcidae comprise a monophyletic group of marine fishes with a worldwide distribution. Centers of high zoarcid diversity occur in the North Atlantic and North Pacific, with important radiations into the Arctic, along southern South America, and into the Southern Ocean around Antarctica. Along with snailfishes (Liparidae), zoarcids form an important component of the non-notothenioid fauna in the subzero shelf waters of Antarctica. We document the anatomy and histology of the brains, cranial nerves, olfactory apparatus, cephalic lateral lines, taste buds, and retinas of three Antarctic zoarcid species, living at depths of 310-939 m, representing three of the nine genera from this region. The primary emphasis is on Ophthalmolycus amberensis, and we provide a detailed drawing of the brain and cranial nerves of this species. Although this brain reflects general perciform neural morphology, it exhibits a reduction of the (optic) tecta and the eminentia granulares and crista cerebellares of the lateral line system. Interspecific differences among the three species are slight. The olfactory rosette consists of three to four lamellae and the nasal sac, contrary to the claim of Fanta et al. ([2001] Antarct Rec, Natl Inst Polar Res, Tokyo 45:27-42), is not in communication with the cephalic lateral line system. Primary olfactory neurons are abundant and converge on branches of the olfactory nerve. Numerous taste buds are located in the lips. All three species lack an ocular choroid rete and have relatively thin retinas with a low cell density and a single bank of rods as the only type of photoreceptor. Neural diversification among Antarctic zoarcids has not involved the evolution of sensory specialists; brain and sensory organ morphologies do not approach the condition seen in primary deep-sea fishes, or even that of some sympatric non-perciform secondary deep-sea fishes, including liparids and muraenolepidids (eel cods). There may be phylogenetic constraints on brain morphology in perciforms such that we do not see extreme specialization in sensory and neural systems for deep habitats. We suggest that the brains and sensory organs of Antarctic zoarcids reflect habitation of 500-2,000-m depths and likely reflect morphologies seen in zoarcids living on continental slopes elsewhere in the world. This balance among the sensory modalities makes zoarcids relatively generalized among secondary deep-sea fishes and may be one of the reasons this opportunistic and adaptable group has been successful in colonizing a variety of emergent and ephemeral habitats.

Animals↗
PubMed1999

Putative mammalian taste receptors: a class of taste-specific GPCRs with distinct topographic selectivity.

Taste represents a major form of sensory input in the animal kingdom. In mammals, taste perception begins with the recognition of tastant molecules by unknown membrane receptors localized on the apical surface of receptor cells of the tongue and palate epithelium. We report the cloning and characterization of two novel seven-transmembrane domain proteins expressed in topographically distinct subpopulations of taste receptor cells and taste buds. These proteins are specifically localized to the taste pore and are members of a new group of G protein-coupled receptors distantly related to putative mammalian pheromone receptors. We propose that these genes encode taste receptors.

Animals↗
PubMed2002

The dynamic expression pattern of B lymphocyte induced maturation protein-1 (Blimp-1) during mouse embryonic development.

We have analyzed the spatial and temporal patterns of B lymphocyte-induced maturation protein-1 (Blimp-1) expression during mouse embryonic development. Blimp-1 expression is induced early in the anterior definitive endoderm, mesoderm of head process, and prechordal plate. In ectoderm-derived tissues at later stages, Blimp-1 expression is found in the primitive photoreceptors of neural retina, in differentiated epithelial cells of epidermis, tongue, oral and nasal cavities, and in the precursors of internal root sheaths of hair follicles. In mesoderm-derived tissues, Blimp-1 expression is observed in splanchnopleure, a subset of somatopleure-derived cells in limb buds, and myotomes of somites. Blimp-1 is also expressed in mesenchyme of developing hand plates, digits, branchial arches, nasal processes, and external genitalia. Blimp-1 is present in mesenchyme-derived chondroblasts, supporting cells of taste buds, and papilla of teeth, hair follicles and taste buds. In endoderm-derived tissues, Blimp-1 expression in the foregut region is restricted to a subset of epithelial cells at the headfold stage while expression in the endodermal epithelium of midgut and hindgut persists from the headfold stage to birth. Finally, Blimp-1 is expressed in the migrating primordial germ cells.

Animals↗
PubMed1993

Genetic and pathological taste variation: what can we learn from animal models and human disease?

The study of patients with taste disorders (i.e. 'experiments of nature') suggests that the old tongue maps (e.g. sweet on the tip, bitter on the back) that often appear in textbooks are wrong. If they were correct, severing the taste nerves that innervate the front of the tongue would result in a loss of the ability to taste sweet, etc. This does not occur. Severing these nerves has little effect on everyday taste experience because taste nerves inhibit one another. Damaging one nerve abolishes its ability to inhibit others and the release-of-inhibition compensates for the damage. There is sometimes a clinical cost for this redundancy; release-of-inhibition can produce taste phantoms. Genetic variation in taste ability occurs across and within species. For example, about 25% of humans are relatively unresponsive to a variety of sweet and bitter compounds (non-tasters) while another 25% are unusually responsive (supertasters). Supertasters have about four times as many taste buds as non-tasters and have smaller and more densely packed fungiform papillae. Since there are pain fibres associated with taste buds, supertasters are unusually responsive to the oral burn of spices.

Animals↗
PubMed1982

On the morpho-histology of the alimentary tract in the Indian climbing perch, Anabas testudineus (Bloch), in relation to food and feeding habits.

Functional morpho-histology of the alimentary tract of the Indian Climbing perch, Anabas testudineus (BLOCH) has been described. The fish possesses a wide, slightly upturned mouth. The presence of jaw, vomerine, palatine, pharyngeal, and horny pad teeth in the bucco-pharyngeal region indicates the carnivorous feeding habit of the fish. Gill-rakers are toothed but the tongue is edentulous. The latter helps in manipulation of larger prey. The nature and disposition of the taste buds in the lips and bucco-pharyngeal region indicate that the fish procures its food primarily by taste and secondarily by sight. Taste buds are also present in the middle oesophagus which indicates that the gustatory sense extends upto this region. The surface epithelium of the cardiac stomach is conspicuous in having specific mucous cells. The pyloric stomach indicates a more primitive nature due to the presence of tubular mucous glands or pyloric glands. The number of pyloric caeca is 4. The intestine is slightly looped and the dimensionless RLG (Relative Length of the Gut) is 0.42. An ileo-rectal valve and the mucosal folds distinguish the rectum from the intestine.

Animals↗
PubMed1999

Anion size of sodium salts and simple taste reaction times.

Simple taste reaction times (RT) and taste intensities were measured in adult humans for 100-mM aqueous solutions of sodium chloride, acetate, glutamate, ascorbate, and gluconate flowed over the anterodorsal tongue with a closed liquid delivery system. Results from 12 subjects showed a significant increase in RT with molecular weight of the tastant, and a correlation of 0.941 between RT and the square roots of anionic weights. A multiple regression analysis controlling for perceived taste intensity indicated that RT increased linearly with the square root of the anionic weight. These findings support a model that includes both the permeability of ions through the tight junctions between the taste receptor cells of fungiform papillae taste buds and the effects of ions at apical portions of the receptor cells. They also suggest that gustatory transduction of sodium salts in humans normally involves intercellular spaces of taste buds as part of the functional sensory structures, in addition to individual taste receptor cells.

Adolescent↗
PubMed1976

[The encephalus of the pond-loach, Misgurnus fossilis (L.), 1758 (fish, teleosts, Cobitidae). An example of sexual dimorphism].

The brain of the Pond-loach (Misgurnus fossilis) is very closely related to that of Cyprinidae. In the Medulla oblongata, the facial lobe-in relation with the skin taste buds, especially on the barbels-is bigger than the vagal lobes-which are related with the mouth taste buds. The intraspecific relations between brainweight and bodyweight or various body lengths show a real sexual dimorphism (brain dimegaly). The interspecific brain-bodyweight relationship shows an allometric coefficient of 0.505 in males and 0.485 in females, very close to that of the Rainbow trout. The encephalization index (63) is very close to that of the Tench, and a little lower than that of the Cyprinidae as a whole.

Animals↗
PubMed2006

Toxic effects on gustatory function.

A large number of substances and disease processes may impact the sense of taste. Toxic substances may cause taste dysfunction from their effects on the gustatory system from the salivary gland, to the taste bud, to the central neural pathways. A number of external toxins, including industrial compounds, tobacco, and alcohol, may adversely affect taste, most commonly through local effects in the oral cavity. Blood-borne toxins, such as medications and those present in autoimmune and other systemic disorders (e.g. renal or liver failure), have access to all parts of the gustatory system, and thus may exhibit varied effects on taste function. An understanding of these potential toxins and their impact on gustation will help physicians better recognize, and potentially limit the impact of such taste alterations on their patients.

Diabetes Complications↗
PubMed2001

Cavefish as a model system in evolutionary developmental biology.

The Mexican tetra Astyanax mexicanus has many of the favorable attributes that have made the zebrafish a model system in developmental biology. The existence of eyed surface (surface fish) and blind cave (cavefish) dwelling forms in Astyanax also provides an attractive system for studying the evolution of developmental mechanisms. The polarity of evolutionary changes and the environmental conditions leading to the cavefish phenotype are known with certainty, and several different cavefish populations have evolved constructive and regressive changes independently. The constructive changes include enhancement of the feeding apparatus (jaws, taste buds, and teeth) and the mechanosensory system of cranial neuromasts. The homeobox gene Prox 1, which is expressed in the expanded taste buds and cranial neuromasts, is one of the genes involved in the constructive changes in sensory organ development. The regressive changes include loss of pigmentation and eye degeneration. Although adult cavefish lack functional eyes, small eye primordia are formed during embryogenesis, which later arrest in development, degenerate, and sink into the orbit. Apoptosis and lens signaling to other eye parts, such as the cornea, iris, and retina, result in the arrest of eye development and ultimate optic degeneration. Accordingly, an eye with restored cornea, iris, and retinal photoreceptor cells is formed when a surface fish lens is transplanted into a cavefish optic cup, indicating that cavefish optic tissues have conserved the ability to respond to lens signaling. Genetic analysis indicates that multiple genes regulate eye degeneration, and molecular studies suggest that Pax6 may be one of the genes controlling cavefish eye degeneration. Further studies of the Astyanax system will contribute to our understanding of the evolution of developmental mechanisms in vertebrates.

Animals↗
PubMed1978

Liquid-sensitive laryngeal receptors in the developing sheep, cat and monkey.

1. Action potentials were recorded from single afferent units of the superior laryngeal nerves in neonatal and adult sheep, cats and monkeys when liquids were passed over the laryngeal mucosa. 2. Two types of mucosal receptors, sensitive to water but not to isotonic saline, were found in each species from birth. The most common type of unit responded after a short latency (less than 1 sec), discharged maximally in the first 1-3 sec and became inactive when the stimulus was withdrawn. The other type responded only after several seconds, the discharges gradually increasing in frequency and continuing after removal of the stimulus. 3. Reproducible responses were elicited by tactile stimulation of the laryngeal mucosa over the receptive field of each of the long-latency units. Fewer than 50% of the short-latency units were excited, the remainder responding only unreproducibly to firm pressure. 4. Short-latency, but not long-latency, units responded to milks, gastric contents, saliva and isotonic solutions of sugars. 5. The responses of long-latency units to water were often modified by, but rarely dependent on, reflexly evoked activity in laryngeal muscles. 6. The conduction velocities of afferent fibres of water sensitive units ranged from 22 to 49 m/sec, and differed little from those of water-insensitive laryngeal mechanoreceptors. 7. Histological examination of the laryngeal mucosa showed that taste buds were present in lambs from birth whereas they developed post-natally in kittens and monkeys. The evidence suggests that taste buds were not associated with water-sensitive units.

Action Potentials↗
PubMed2004

[Etiology, diagnostic and therapeutic management of taste disorders].

Taste disorders can be subdivided in ageusia, which is the inability to detect any qualitative gustatory sensation and hypogeusia, which is a decreased sensitivity to all tastants. Dysgeusia or pargeusia is a distortion or perversion in the perception of a tastant in contrast to phantosmia, which is a perception of taste that occurs in the absence of a tastant. The site of lesion can usually be determined by history and clinical examination. History taking should always include the assessment of current and former medication. Conditions that interfere with access of a tastant to the taste bud are differentiated from conditions that either injure the receptor cell or damage the gustatory afferent nerves and the central pathways. Psychophysical taste evaluation includes identification of quality using sprays or taste strips and testing of intensity perception measuring threshold using the 3-drop technique. Moreover, measurement of taste in localized areas can be performed either with conventional chemicals or using an electrogustometer. Gustatory evoked potentials are not yet routinely elicited. Therapy has to be planned according to the cause of the disorder.

Diagnosis, Differential↗
PubMed2000

Receptor and transduction processes for umami taste.

The unique taste of umami argues for a specific receptor at the taste cell level. The taste synergism between monosodium glutamate (MSG) and certain 5'-ribonucleotides provides a pharmacologic test for hypothetical mechanisms of umami taste. Early neurophysiologic and biochemical studies demonstrated specific recognition of L-glutamate by taste tissue and suggested that the synergism found with certain 5'-ribonucleotides was due to a peripheral event. The search for a receptor for umami relies at present on the data in the literature on central nervous system (CNS) glutamate receptors. These data distinguish several classes of receptors on the bases of pharmacologic properties and mode of action. Two hypotheses now seek to explain umami taste transduction. One states that umami is transduced by an N-methyl-D-aspartate (NMDA)-type glutamate ion channel receptor, the other that this taste is transduced via a metabotropic-type glutamate receptor. Evidence for the first hypothesis derives from earlier reconstitution studies, revealing a glutamate-stimulated ion channel conductance whose kinetics were affected by 5'-ribonucleotides. Additional evidence is provided from more recent calcium-imaging and patch-clamp studies, both showing that an ionotropic-type receptor on rodent taste cells mediates glutamate-induced depolarization. Evidence for the second mechanism derives from studies that located the message for an metabotropic-type (mGluR4) receptor to rat taste buds, and from whole-cell patch-clamp recordings that revealed sustained cellular conductances to glutamate and an mGluR4 agonist. It appears likely that both mechanisms are involved in umami taste transduction, suggesting the possibility that reception and transduction of the umami signal constitute a collective property of a number of cells within the taste bud.

Animals↗
PubMed2000

Rapid entry of bitter and sweet tastants into liposomes and taste cells: implications for signal transduction.

Some amphipathic bitter tastants and non-sugar sweeteners are direct activators of G proteins and stimulate transduction pathways in cells not related to taste. We demonstrate that the amphipathic bitter tastants quinine and cyclo(Leu-Trp) and the non-sugar sweetener saccharin translocate rapidly through multilamellar liposomes. Furthermore, when rat circumvallate (CV) taste buds were incubated with the above tastants for 30 s, their intracellular concentrations increased by 3.5- to 7-fold relative to their extracellular concentrations. The time course of this dramatic accumulation was also monitored in situ in rat single CV taste buds under a confocal laser-scanning microscope. Tastants were clearly localized to the taste cell cytosol. It is proposed that, due to their rapid permeation into taste cells, these amphipathic tastants may be available for activation of signal transduction components (e. g., G proteins) directly within the time course of taste sensation. Such activation may occur in addition to the action of these tastants on putative G protein-coupled receptors. This phenomenon may be related to the slow taste onset and lingering aftertaste typically produced by many bitter tastants and non-sugar sweeteners.

Animals↗
PubMed2001

Morphological differentiation of taste organs in the ontogeny of Salamandra salamandra.

Morphological studies presented here provide additional cytological evidence that in the postnatal development of Salamandra salamandra there are two successive generations of taste organs: premetamorphic taste buds (TBs) in larval forms and taste disks (TDs) in postmetamorphic animals. The TBs have been found in the epithelium of the whole oropharyngeal cavity of larval forms, while in adults TDs appear only at the end of metamorphosis. The TDs can be papillary (or fungiform) on the soft (secondary) tongue and non-papillary outside the tongue. Two main cyto-morphological criteria distinguishing TDs from TBs have been established: (1) high differentiation of "nonsensory" components of a taste organ into several kinds of cells (often named "associate cells")--at least mucous cells and, separating them, wing cells; (2) a considerably larger area of the sensory epithelium than that in TBs, as the consequence of the large size of the mucous cells. In contrast to TDs each TB consists of longitudinally elongated supporting cells and taste cells, as well as of horizontally oriented basal cells, adjacent to the basement membrane. The sensory area in TBs measures 10-12 microm in diameter, while that in TDs has diameter of 45-90 microm. The anlage of the secondary tongue appears as a small folding of the floor epithelium just in front to the tip of the primary tongue in larvae 3 cm long, and is definitely formed in an animal with body length of about 6 cm.

Animals↗
PubMed1997

Serotonin modulates voltage-dependent calcium current in Necturus taste cells.

Necturus taste buds contain two primary cell types: taste receptor cells and basal cells. Merkel-like basal cells are a subset of basal cells that form chemical synapses with taste receptor cells and with innervating nerve fibers. Although Merkel-like basal cells cannot interact directly with taste stimuli, recent studies have shown that Merkel-like basal cells contain serotonin (5-HT), which may be released onto taste receptor cells in response to taste stimulation. With the use of whole cell voltage clamp, we examined whether focal applications of 5-HT to isolated taste receptor cells affected voltage-activated calcium current (I(Ca)). Two different effects were observed. 5-HT at 100 microM increased I(Ca) in 33% of taste receptor cells, whereas it decreased I(Ca) in 67%. Both responses used a 5-HT receptor subtype with a pharmacological profile similar to that of the 5-HT1A receptor, but the potentiation and inhibition of I(Ca) by 5-HT were mediated by two different second-messenger cascades. The results indicate that functional subtypes of taste receptor cells, earlier defined only by their sensitivity to taste stimuli, may also be defined by their response to the neurotransmitter 5-HT and suggest that 5-HT released by Merkel-like basal cells could modulate taste receptor function.

Animals↗
PubMed2002

Acetylcholine increases intracellular Ca2+ in taste cells via activation of muscarinic receptors.

Previous studies suggest that acetylcholine (ACh) is a transmitter released from taste cells as well as a transmitter in cholinergic efferent neurons innervating taste buds. However, the physiological effects on taste cells have not been established. I examined effects of ACh on taste-receptor cells by monitoring [Ca2+]i. ACh increased [Ca2+]i in both rat and mudpuppy taste cells. Atropine blocked the ACh response, but D-tubocurarine did not. U73122, a phospholipase C inhibitor, and thapsigargin, a Ca2+-ATPase inhibitor that depletes intracellular Ca2+ stores, blocked the ACh response. These results suggest that ACh binds to M1/M3/M5-like subtypes of muscarinic ACh receptors, causing an increase in inositol 1,4,5-trisphosphate and subsequent release of Ca2+ from the intracellular stores. A long incubation with ACh induced a transient response followed by a sustained phase of [Ca2+]i increase. In Ca2+-free solution, the sustained phases disappeared, suggesting that Ca2+ influx is involved in the sustained phase. Depletion of Ca2+ stores by thapsigargin alone induced Ca2+ influx. These findings suggest that Ca2+ store-operated channels may be present in taste cells and that they may participate in the sustained phase of [Ca2+]i increase. Immunocytochemical experiments indicated that the M1 subtype of muscarinic receptors is present in both rat and mudpuppy taste cells.

Acetylcholine↗
PubMed1994

Ca(2+)-dependent Cl- conductance in taste cells from Necturus.

1. Taste responses adapt to a constant chemical stimulus. The present study describes a new ionic conductance in taste cells--a Ca(2+)-dependent anion conductance that may explain taste adaptation. 2. Patch-clamp recordings were made on isolated Necturus taste cells or on taste cells in lingual slices. When Na+ and K+ currents were eliminated with tetrodotoxin (TTX) and tetraethyl-ammonium (TEA) in the bath and replacing K+ with N-methyl-D-glucamine (NMDG+) in the pipette, Ca2+ currents were followed by prolonged outward currents. Outward current was abolished when Ca2+ was substituted with Ba2+ or when Cl- was replaced with large organic anions (methanesulfonate, isethionate, or ascorbate). 3. The outward, Ca-dependent current was reduced by certain agents that block Cl- conductances in other tissues, namely 4-acet-amido-4-isothiocyanostilbene-2,2-disulfonic acid (SITS) and 4,4-diisothiocyanostilbene-2,2-disulfonic acid (DIDS). However, other Cl- channel blockers--9-AC, furosemide and an antibody to Cl channels-had little or no specific effect on the Ca-dependent outward current in Necturus taste cells. 4. We postulate that the biological action of this Ca-dependent anion conductance in situ is to terminate depolarizing receptor potentials, even during maintained chemostimulation, thereby playing an important role in chemosensory adaptation and modulation of impulse discharge patterns in taste buds.

Afferent Pathways↗
PubMed2006

Comparative morphological study on the lingual papillae and their connective tissue cores (CTC) in reeves' muntjac deer (Muntiacus reevesi).

The lingual papillae and their connective tissue cores (CTC) from Reeves' muntjac deers (herbivorous artiodactyla) were studied using light and scanning electron microscopy and then compared to those of other mammalian species. At the posterior portion of the tongue, the Reeves' muntjac has a lingual prominence on which large conical papillae are distributed. On the dorsal surface of the anterior tongue, numerous filiform papillae were found. Externally, each filiform papilla consists of a rod-shaped main process and several small accessory processes. Their CTCs consist of 10 or more rod-shaped processes arranged in a horseshoe pattern and several posterior processes forming a small circular pattern. This structure is a common characteristic of artiodactyla, through which Reeves' muntjac deer can be categorized in a position in the artiodactyla class lying between the bighorn sheep and the East African bongo. Fungiform papillae are distributed among the filiform papillae on the anterior portion of the tongue. Large fungiform papillae are also sparsely distributed on the lingual prominence and have several taste buds in the epithelium on the surface. Ten or more vallate papillae are distributed at the postero-lateral area of the lingual prominence and numerous taste buds are distributed in the epithelium of their side.

Africa, Eastern↗