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PubMed1994

Olfaction and gustation in fish: an overview.

Living in an aquatic environment, often devoid of light but rich in dissolved compounds, fish have highly developed chemosensory and chemical signalling systems. The olfactory and gustatory systems comprise the major chemosensory pathways. Despite considerable variations in structural organization of the peripheral olfactory organ throughout fish species, ultrastructural organization of the olfactory sensory epithelium is extremely consistent. The olfactory receptor cell is a bipolar neurone which is directly exposed to the external environment and sends information to the brain by its own axon (cranial nerve I). Four major classes of chemicals have been identified as specific olfactory stimuli and their stimulatory effectiveness characterized: amino acids, sex steroids, bile acids/salts and prostaglandins. Olfactory signals such as those involved in reproduction and feeding may be processed independently through two distinct subsystems: the lateral and medial olfactory systems. The taste buds constitute the structural basis of the gustatory organ. Taste buds may occur not only in the oropharyngeal cavity, but on the whole body surface. Chemical information detected by specialized epithelial cells, gustatory cells, is transmitted to the central nervous system by cranial nerve VII (facial), IX (glossopharyngeal), and X (vagal). Besides diverse sensitivities and specificities for amino acids, fish gustatory receptors detect various organic acids, nucleotides and bile salts. Putative receptors, molecular mechanisms of transduction and the role played by olfaction and gustation in feeding, reproduction, migration and other fish behaviours are discussed.

Animals↗

PubMed1986

A patch-clamp analysis of membrane currents in salamander olfactory receptor cells.

Isolated olfactory receptor cells were obtained from salamander olfactory epithelium and kept in short term culture conditions. They were studied by means of the whole cell patch-clamp technique associated with ionic substitutions and channel blockers. Under physiological ionic gradients, these cells had a resting potential of -39 +/- 10 mV and an input resistance above 2 G omega. Using different channel blockers and ion substitutions, we could separate several distinct components in the overall whole cell current. In most cells, inward current reflected the activation of a TTX resistant conductance which was blocked by cobalt ions. This inward current lasted only for about 5 min of whole cell recording. In a minority of cells, a TTX sensitive sodium current was also observed. The outward K+ current was blocked when the cells were loaded with cesium and tetraethylammonium. It inactivated slowly and incompletely and could act as a depolarization limited in case of intense odour stimulations. Single channel analysis from outside out patches suggested that it corresponded to the activity of 34 pS channels. In some cells a rapidly inactivating K+ current was also present. Single channel activities (27 +/- 6 pS) were commonly recorded with KCl-filled pipettes, at resting or hyperpolarized membrane potentials but not at depolarized potentials. Membrane hyperpolarization increased the open-state probability. A preliminary study with odorant stimulations indicated the existence of a stimulus-induced current probably corresponding to the activation of the chemoreceptive membrane.

Animals↗

PubMed1998

Inhibitors of sensillar esterase block reversibly the responses of moth pheromone receptor cells.

The pheromone of Antherae polyphemus is slowly (within min) degraded by a sensillum lymph specific esterase. The effects of two volatile alkyl-thio-trifluoro-methyl-ketones with alkyl chain length of six (HTFP) and ten carbons (DTFP), which selectively inhibit the activity of the sensillar esterase, were tested. Single sensillum recordings from sensilla trichodea were performed on isolated antennae either held in a continuous stream of clean air, or exposed to an airstream containing one of the esterase inhibitors. Afterwards the antennae were stimulated with the pheromone components (E,Z)-6,11-hexadecadienyl acetate and (E,Z)-6,11-hexadecadienal. Both esterase inhibitors caused a reduction of electrophysiological responses to each of the two pheromone compounds. The DTFP was slightly more effective than HTFP. An almost complete block of the receptor potential amplitude and nerve impulse response was achieved within seconds of exposure to the inhibitors. Responses of both pheromone receptor cells were reduced to the same extent. The half-times of rise and decline of the receptor potential remained unaffected in most cells. The responses to pheromone partially recovered to approximately 50-70% within several min in clean air. An inhibition of the sensillar esterase cannot explain the observed effects. The inhibitors could either react directly with the receptor molecules, thereby inhibiting the action of the pheromone, or bind to the pheromone-binding protein (PBP) and prevent the formation of the pheromone-PBP complex stimulating the receptor.

Animals↗

PubMed2006

A new method for electrophysiological identification of antennal pH receptor cells in ground beetles: the example of Pterostichus aethiops (Panzer, 1796) (Coleoptera, Carabidae).

The responses of antennal taste sensilla of the ground beetle Pterostichus aethiops to 100mM Na(+)-salts and their mixtures with 1 and 10mM NaOH were compared. An increase in pH by 0.3-0.6 units in 100mM Na(+)-salt solutions, caused by the content of 1mM NaOH, was too small, except for alkaline Na(2)HPO(4), to influence the firing rate of the cation cell and pH cell significantly. However, different sensitivity of the two cells to increased pH was clearly demonstrated when the concentration of NaOH in 100mM stimulating salt solutions was increased to 10mM. Increasing pH by 1.2-2 units caused the 1st s firing rate to increase by 140-1050% and 0-26% in the pH cell and cation cell, respectively. Compared to the buffer series method used for identification of the pH receptors in ground beetles earlier, considerably stronger responses of the pH cell to a similar increase in pH were observed when the NaOH method was used for testing. At the same time, undesirable changes in salt ions concentration that occur when stimulating solutions differing by 1-2 pH units are prepared were much smaller using the latter method. Behavioural and ecological relevance of the results is discussed.

Action Potentials↗

PubMedDate not supplied

Issues of gustatory neural coding: where they stand today.

The basic issues of gustatory neural coding are revisited. Questions addressed and conclusions drawn are: (1) what is the physical dimension across which gustatory neurons are sensitive, and upon which taste perceptions are based? The dimension that unites the various taste qualities is not physical, but physiological: a dimension of well-being, bounded by toxins at one extreme and nutrients at the other. (2) How broadly tuned are taste cells across the dimension? There are instances of specificity, but most mammalian taste cells respond to a range of qualities. (3) Are there basic taste qualities? Sweet, salty, sour, and bitter are widely accepted as basic tastes. Umami and starch tastes are considered basic by some. (4) Is taste topographically organized? There is some degree of physical separation among neurons most responsive to different taste qualities, but this does not appear to be sufficient precision to act as a meaningful coding mechanism. (5) Are there gustatory neuron types? Neurons, separated into categories according to their response profiles, respond as members of their category to the challenges of conditioned aversions and preferences, sodium deprivation, hyperglycemia, and receptor blockade, while cells from other categories react differently. This indicates the existence of functionally distinct types of taste cells. (6) Is the quality signal coded within the activity of the single most appropriate category of neurons, or is it carried by the pattern of response across neuronal categories? Both the breadth of responsiveness and the logical ambiguity of the signal in any one category of neurons argue that the taste message is carried by a pattern of activity across gustatory neuron types.

Animals↗

PubMed1999

Two heteromeric kinesin complexes in chemosensory neurons and sensory cilia of Caenorhabditis elegans.

Chemosensation in the nervous system of the nematode Caenorhabditis elegans depends on sensory cilia, whose assembly and maintenance requires the transport of components such as axonemal proteins and signal transduction machinery to their site of incorporation into ciliary structures. Members of the heteromeric kinesin family of microtubule motors are prime candidates for playing key roles in these transport events. Here we describe the molecular characterization and partial purification of two heteromeric kinesin complexes from C. elegans, heterotrimeric CeKinesin-II and dimeric CeOsm-3. Transgenic worms expressing green fluorescent protein driven by endogenous heteromeric kinesin promoters reveal that both CeKinesin-II and CeOsm-3 are expressed in amphid, inner labial, and phasmid chemosensory neurons. Additionally, immunolocalization experiments on fixed worms show an intense concentration of CeKinesin-II and CeOsm-3 polypeptides in the ciliated endings of these chemosensory neurons and a punctate localization pattern in the corresponding cell bodies and dendrites. These results, together with the phenotypes of known mutants in the pathway of sensory ciliary assembly, suggest that CeKinesin-II and CeOsm-3 drive the transport of ciliary components required for sequential steps in the assembly of chemosensory cilia.

Amino Acid Sequence↗

PubMed1994

Transmembrane signalling by the chimeric chemosensory receptors of Escherichia coli Tsr and Tar with heterologous membrane-spanning regions.

The serine and aspartate chemosensory receptors (Tsr and Tar) of Escherichia coli have two membrane-spanning regions TM1 and TM2. To investigate their roles in transmembrane signalling, we constructed two chimeric receptors from Tsr and Tar with heterologous combinations of TM1 and TM2: the N-terminus of one receptor, including TM1 and the periplasmic domain, was fused to the C-terminus of the other, beginning with TM2. Both of the chimeric receptor genes rescued the chemotactic defect of a receptorless E. coli strain, indicating that the chimeric receptors are functional. Their apparent affinities for the specific ligands were the same as those of Tsr or Tar. Therefore, as far as transmembrane signalling abilities are concerned, the TM2 regions of Tsr and Tar are interchangeable, suggesting that sequence-specific interaction between TM1 and TM2 may not be required for the signal transmission across the membrane. The cells expressing either of the chimeric receptors, however, showed 'smooth', biased, basal swimming patterns. Moreover, they adapted quickly after stimulation with the repellent glycerol. This rapid adaptation was observed even in the methyltransferase-defective strain. Therefore, exchange of TM2 might impose structural constraints on the chimeric receptors that stabilize conformations which elicit smooth swimming.

Adaptation, Physiological↗

PubMed1992

Mechanisms by which cancer chemotherapeutic drugs induce emesis.

Because the area postrema seems essential for chemotherapy-induced vomiting, both circulating and/or neurally mediated stimuli in this area could trigger the emetic response. In our laboratories results of cross-circulation and direct intracerebroventricular infusion experiments in dogs do not support a role for circulating substances. The large increases in serum vasopressin induced by cisplatin were not blocked by inhibitors of the angiotensin-converting enzyme. In the ferret inhibition of serotonin synthesis with p-chloro-phenylalanine, administration of selective antagonists of 5-hydroxy-tryptamine3 (5-HT3) receptors, or visceral deafferentation inhibited the emetic response evoked by cisplatin or high-dose cyclophosphamide. The results suggest that serotonin plays an important role and that peripheral neural mechanisms are involved in the emetic response. The strong antiemetic efficacy of selective 5-HT3 antagonists also has been confirmed in humans. In cancer patients high-dose cisplatin increased the plasma and urinary levels of 5-hydroxy-indoleacetic acid (5-HIAA), but did not affect platelet and free plasma serotonin. The changes in 5-HIAA levels paralleled the onset and development of vomiting. No evidence of serotonin depletion has been obtained after high-dose cisplatin. Dacarbazine, another strongly emetogenic agent, increased urinary 5-HIAA; however, only small increases in 5-HIAA were produced with low-dose cisplatin or cyclophosphamide-containing regimens. Thus, emetogenicity appears to be directly related to the ability of the cytotoxic agent to release serotonin. In humans, antiemetics such as ondansetron, metoclopramide, and dexamethasone did not effect high-dose cisplatin-induced increases in serotonin metabolism. Therefore, these antiemetics seem not to affect the amount of serotonin released. The mechanism by which chemotherapeutic drugs induce serotonin release is unknown; however, release may occur by direct cytotoxicity on the gastrointestinal mucosa, including the enterochromaffin cells. Delayed emesis appears to be mediated by 5-HT3-independent mechanisms. It is proposed that emesis that develops despite high-dose ondansetron (residual emesis) should be considered delayed emesis. Residual and delayed episodes of emesis have similar time courses, are characterized by very mild emetic episodes and poor response to 5-HT3 antagonists, and are not associated with increases in serotonin metabolism.

Animals↗

PubMed1993

Electrochemical detection of catecholamine release from rat carotid body in vitro.

Neurotransmitter secretion from carotid body glomus cells is hypothesized to be an essential element of chemotransduction. To address one aspect of this hypothesis, catecholamine release in response to hypoxic hypoxia and histotoxic hypoxia was examined using electrically treated carbon-fiber microelectrodes placed in rat carotid bodies in vitro. Carotid bodies of mature rats were removed, along with a portion of the sinus nerve, and suspended in oxygenated (95% O2-5% CO2) Ringer saline at 35 degrees C. The microelectrode differential current after a 50-mV step was recorded over the potential range of -300 to +500 mV. In some preparations, a suction electrode applied to the sinus nerve recorded single-fiber chemoreceptor afferent activity. Stimulation by severe hypoxia (Po2 approximately 0-10 Torr for 3 min, n = 10) and cyanide (2 mM for 2 min) caused an increase in sinus nerve activity and an increase in the carbon-fiber electrode current at a potential corresponding to the oxidation potential of dopamine. As measured in the amperometric mode (constant voltage), tissue catecholamine was 0.35 +/- 0.05 microM (n = 6) and increased to 1.64 +/- 0.43 microM by 1 min of severe hypoxia or to 1.06 +/- 0.17 microM at 2 min of moderate hypoxia (Po2 approximately 50 Torr). Exposure to calcium-free Ringer saline before hypoxia ablated the increase in electrode current, and the response was restored after reperfusion with calcium-containing saline. Repeated exposures to hypoxia (3-min duration) every 15 min resulted in significantly smaller nerve and catecholamine responses. By the third hypoxia exposure, nerve and catecholamine responses were diminished by 30-50%.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗

PubMed1998

[Electron microscopy studies of the human vomeronasal organ].

The vomeronasal organ, or Jacobson's organ, is essential for pheromone detection and reproductive behavior in most mammals. In humans, it has been described as a blind diverticulum in the anterior nasal septum, but without a documented function. The purpose of this study is to describe the fine structure of the human adult vomeronasal organ in 14 specimens. Our studies showed a duct-like invagination of the epithelium that was surrounded by numerous exocrine glands with short ducts. The fine structure of these glands suggested a serous secretion. In the depth of the invagination, pseudostratified columnar epithelial cells were seen that had plump processes, kinocilia and microvilli at the apical cell membrane. Several cell types were seen that differed regarding their organelles and electron density, with light sensory cells exhibiting neurofilaments. Underneath the typical basement membrane, numerous myelinated and unmyelinated axons were present in the very vascular lamina proprion. These morphological findings are unique in the human body and suggest that a chemosensory epithelium corresponding to a vomeronasal organ may exist. Its central connections and the possible functional significance of this tubed organ for pheromone detection are unknown and need further study.

Adolescent↗

PubMed2002

C. elegans responds to chemical repellents by integrating sensory inputs from the head and the tail.

The phasmids are bilateral sensory organs located in the tail of Caenorhabditis elegans and other nematodes. The similar structures of the phasmids and the amphid chemosensory organs in the head have long suggested a chemosensory function for the phasmids. However, the PHA and PHB phasmid neurons are not required for chemotaxis or for dauer formation, and no direct proof of a chemosensory function of the phasmids has been obtained. C. elegans avoids toxic chemicals by reversing its movement, and this behavior is mediated by sensory neurons of the amphid, particularly, the ASH neurons. Here we show that the PHA and PHB phasmid neurons function as chemosensory cells that negatively modulate reversals to repellents. The antagonistic activity of head and tail sensory neurons is integrated to generate appropriate escape behaviors: detection of a repellent by head neurons mediates reversals, which are suppressed by antagonistic inputs from tail neurons. Our results suggest that C. elegans senses repellents by defining a head-to-tail spatial map of the chemical environment.

Animals↗

PubMed2003

Expression of antisense bcl-2 cDNA abolishes tumorigenicity and enhances chemosensitivity of human malignant glioma cells.

Bcl-2 is a key antiapoptotic protein, and it confers survival advantages on many types of tumors by inhibiting apoptotic cell death. Malignant gliomas are the most common primary central nervous system tumors, but the role of bcl-2 in these tumors has not been defined. We investigated the impact of bcl-2 on malignant gliomas by suppressing its expression. Antisense human bcl-2 cDNA was transfected into human malignant glioma cells. The effects of bcl-2 protein down-regulation on glioma cell morphology, in vitro tumor growth, and tumorigenicity in nude mice, as well as chemosensitivity to cisplatin, were studied. Expression of antisense bcl-2 cDNA decreased bcl-2 protein by more than sixfold. Antisense bcl-2 stable transfectants (AS-bcl-2) showed profound morphological change and markedly retarded cell growth in vitro. Transplantation of AS-bcl-2 cells resulted in no tumor formation, whereas backbone plasmid transfectant control formed tumors in each mouse transplanted. Expression of antisense bcl-2 in glioma cells resulted in significantly increased cytotoxicity of cisplatin. In conclusion, antisense bcl-2 expression can effectively reduce glioma survival, including retarding in vitro growth, complete loss of tumorigenicity, and significantly enhanced cisplatin cytotoxicity. These results suggest that bcl-2 plays an important role in glioma malignancy and chemoresistance. Development of strategies targeted at bcl-2 has the potential to advance treatment for malignant gliomas.

Animals↗

PubMed1994

Carbonic anhydrase and CO2 chemoreception in the pulmonate snail Helix aspersa.

We have studied the effects of carbonic anhydrase inhibition on the hypercapnic ventilatory response of the pulmonate snail, Helix aspersa, in an isolated brain-pneumostome preparation. We found that the cell permeant carbonic anhydrase inhibitor, acetazolamide (ACTZ), increased pneumostomal opening and ventilation during normocapnia (2-3% CO2) and decreased the rate of pneumostomal response to step changes in CO2 (4.5%), but did not change the steady-state ventilatory response to elevated CO2 (4.5%) compared to the inactive ACTZ analogue, N2-substituted 2-acetylamino-1,3,4-thiadiazole (Cl 13850). In contrast, the cell impermeant carbonic anhydrase inhibitor, quartenary ammonium sulfonilamide (QAS), had no effect on the pneumostomal response to CO2 compared to Cl 13850. Using Hansson's histochemical technique to stain for carbonic anhydrase activity, we identified a small number of neurons in the subesophageal ganglia that exhibited carbonic anhydrase activity. Some of these cells were in the region of CO2-sensitivity. In conclusion, carbonic anhydrase inhibition slows the ventilatory response to rapid changes in CO2, but does not affect the intrinsic ability of H. aspersa to respond to CO2. The ventilatory effects of carbonic anhydrase inhibition may be attributed to the intracellular actions of the carbonic anhydrase enzyme.

Animals↗

PubMed1991

Chemosensory neurons with overlapping functions direct chemotaxis to multiple chemicals in C. elegans.

The functions of the 11 classes of exposed chemosensory neurons of C. elegans were tested by killing cells with a laser microbeam. One pair of neurons, the ASE neurons, is uniquely important for chemotaxis: killing the ASE neurons greatly reduced chemotaxis to cAMP, biotin, Cl-, and Na+. Additional chemosensory function is distributed among several other cell types. Thus, 3 pairs of chemosensory neurons (ADF, ASG, and ASI) contribute to a residual response to cAMP, biotin, Cl-, and Na+ after ASE is killed. Chemotaxis to lysine similarly depends on the partly redundant functions of 4 pairs of chemosensory neurons (ASE, ASG, ASI, and ASK). The combined activity of several neuron types that act in parallel might increase the fidelity of chemotaxis.

Animals↗

PubMed2005

Osteocalcin-immunoreactive neurons in the vagal and glossopharyngeal sensory ganglia of the rat.

Immunohistochemistry for osteocalcin (OC) was performed on the rat vagal and glossopharyngeal sensory ganglia. OC-immunoreactive (IR) neurons were detected in the jugular (10%), petrosal (11%) and nodose ganglia (6%). The cell size analysis demonstrated that OC-IR neurons were predominantly small to medium-sized in the jugular ganglion (mean+/-S.D.=356.3+/-192.2 microm(2), range=86.5-831.5 microm(2)). On the other hand, such neurons were medium-sized to large in the petrosal (mean+/-S.D.=725.6+/-280.7 microm(2), range=124.7-1540.4 microm(2)) and nodose ganglia (mean+/-S.D.=857.5+/-330.2 microm(2), range=367.1-1608.0 microm(2)). In the circumvallate papilla, OC-IR nerve fibers were located in the vicinity of taste buds. Some taste bud cells were also immunoreactive for the calcium-binding protein (CaBP). In the carotid body, however, OC-IR nerve fibers could not be detected. Retrograde tracing with fluorogold revealed that OC-IR nerve fibers in the circumvallate papilla mainly originated from the petrosal ganglion. These findings may suggest that OC-IR petrosal neurons have chemoreceptive function in the tongue.

Animals↗

PubMed2005

Gustatory perception and behavior in Drosophila melanogaster.

The sense of taste is essential for the survival of virtually all animals. Considered a 'primitive sense' and present in the form of chemotaxis in many bacteria, taste is also a sense of sophistication in humans. Regardless, taste behavior is a crucial activity for the world's most abundant (insects) and most successful (mammals) inhabitants, providing a means of discrimination between nutrient-rich substrates, such as sugars and amino acids, from harmful, mostly bitter-tasting chemicals present in many plants. In this review, we present an update on progress in understanding taste perception in the model fruit fly Drosophila melanogaster. An introduction to the fly's taste system will be presented first, followed by a description of relevant behavioral assays developed to quantify taste perception at the organismal level and a short overview of electrophysiological studies performed on taste cells. The focal point will be the recent molecular-genetic investigations of the gustatory receptor (Gr) genes, which is complemented by a comparison between Drosophila and mammalian taste perception and transduction. Finally, we provide a perspective on the future of Drosophila taste research, including three specific proposals that seem uniquely applicable to this exquisite model system and cannot, at least currently, be pursued elsewhere.

Animals↗

PubMed2004

Sensory systems in amphioxus: a window on the ancestral chordate condition.

Amphioxus has an assortment of cells and organs for sensing light and mechanical stimuli. Vertebrate counterparts of these structures are not always apparent, and a strong case can be made for homology in only a few instances. For example, amphioxus has anatomically simple but plausible homologs of both the pineal and paired eyes of vertebrates. Placodal and neural crest derivatives are, however, more problematic: the evidence for an olfactory system in amphioxus is only circumstantial and, despite the variety of secondary sensory cell types that occur on the body surface in amphioxus, none are obvious homologs of vertebrate taste buds, neuromasts or acoustic hair cells. A useful perspective can nevertheless be gained by examining differences in amphioxus and vertebrate development, specifically how each specifies and positions sensory precursors, controls their proliferation, and deploys them through the body. The much larger size of vertebrate embryos and the need to cope developmentally with increased scale and cell numbers may account for some key vertebrate innovations, including placodes and neural crest. The presence or absence of specific structural adaptations, like the latter, is therefore less useful for judging homology between amphioxus and vertebrates than shared features of specific cell types. It is also clear that the duration of embryogenesis in vertebrates has been significantly extended in comparison with ancestral chordates so as to incorporate events that would originally have occurred during the post-embryonic growth period, including events of neurogenesis. Consequently, no scenario for the origin of vertebrates can be considered complete unless it deals explicitly with the whole of the life history and changes to it.

Animals↗

PubMed1993

Ca2+ transport and chemoreception in Paramecium.

Intracellular Ca2+ levels in Paramecium must be tightly controlled, yet little is understood about the mechanisms of control. We describe here indirect evidence that a phosphoenzyme intermediate is the calmodulin-regulated plasma membrane Ca2+ pump and that a Ca(2+)-ATPase activity in pellicles (the complex of cell body surface membranes) is the enzyme correlate of the plasma membrane pump protein. A change in Ca2+ pump activity has been implicated in the chemoresponse of paramecia to some attractant stimuli. Indirect support for this is demonstrated using mutants with different modifications of calmodulin to correlate defects in chemoresponse with altered Ca2+ homeostasis and pump activity.

Animals↗