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PubMed2004

Interactions of chemostimuli at the single cell level: studies in a model system.

The responses of afferent chemosensory fibres of the carotid body to individual chemostimuli have long been established. However, the mechanisms underlying the multiplicative interactions of these stimuli (i.e. how the combined effects of hypoxia and hypercapnia exert a greater effect on afferent nerve discharge than the sum of their individual effects) have not been elucidated. Using the membrane hypothesis for carotid body chemoreception, in which chemostimuli inhibit type I cell K+ channels, leading to depolarization, voltage-gated Ca2+ entry and hence the triggering of exocytosis, this article considers data acquired in isolated type I carotid body cells and model chemoreceptor (PC12) cells to attempt to explain stimulus interactions. Whilst stimulus interactions are not clearly evident at the level of K+ channel inhibition or rises of [Ca2+]i, they are apparent at the level of transmitter release. Thus, it is clear that individual chemoreceptor cells can sense multiple stimuli, and that interactions of these stimuli can produce greater than additive effects in terms of transmitter release.

Animals↗
PubMed2005

Neurotransmitters in carotid body development.

This review examines the possible role of neurotransmitters present in the carotid body on the functional expression of chemosensory activity during postnatal development. In particular, dopamine, acetylcholine, adenosine and neuropeptides are reviewed. Evidence to date shows involvement of these transmitters in signal transmission from the chemoreceptor cells to chemosensory afferent fibers of the sinus nerve, with clear age- or maturation-dependence of some aspects. However, it remains unresolved whether these neurotransmitters, some of which are expressed in the carotid body before birth, are directly involved in the maturation of the functional properties of the carotid chemoreceptors in sensing oxygen or other stimuli during postnatal development.

Animals↗
PubMed1980

The ultrastructural characteristics of the apical cell in the neuroepithelial bodies of the toad lung (Bufo marinus).

The cytological features and membrane specialisations of neuroepithelial cells (apical cells) in direct contact with the lumen of the lung were studied with transmission and scanning electron microscopy. The luminal surface of the apical cell is characterised by microvilli, a cilium with an 8 + 1 microtubular pattern and numerous coated vesicles. The cytoplasmic region immediately beneath the luminal plasma membrane contains numerous smooth-walled vesicles, tubules and microtubules, a few microfilaments and dense granules (15-20 nm in diameter). The luminal pole of the cell is marked off from the basal or vascular pole by a well-defined terminal web associated with junctional complexes. Protrusion of the luminal pole occurs as a transient phenomenon and is accompanied by a pinching in of the cell at the terminal web. It is proposed that the distinctive features of the luminal pole of the apical cell are comparable to those of recognised chemoreceptor cells. It is also proposed that in view of the common features of apical and basal cells the apical cell functions as a receptor/transducer and the basal cells served as an accessory source of peptides/5-hydroxytryptamine to be released on stimulation of the apical cell. Furthermore, we have drawn attention to the structural heterogeneity of the neuroepithelial bodies in various vertebrate classes.

Animals↗
PubMed1984

Ultrastructural and histochemical changes in the frog taste organ following denervation.

The fine structure of the taste organ in the Rana catesbeiana was observed by light and electron microscopy. The taste organ consists of three distinct cell types, the taste, supporting and basal cells as well as nerve elements. The present findings suggest that the taste cell might function not only as a chemoreceptor cell, but also as a paracrine cell. The basal cell also may have a dual function as both mechanoreceptor and paracrine cell. Furthermore, taste organs have been examined at intervals from 3 hrs to 120 days after sectioning of the glossopharyngeal nerves. The taste organs were almost intact throughout the experimental period after denervation and even after ceasing to produce impulses from chemical or mechanical stimuli. The dense-cored vesicles of the taste or basal cells, which may possess a paracrine action, still remain in the taste organ even 120 days after denervation. It can be concluded that the morphological integrity of the frog taste organ does not absolutely need the presence of the gustatory fibers in contrast to the nerve-dependent nature of the mammalian taste bud.

Adenosine Triphosphatases↗
PubMed1988

Electron microscopic immunocytochemical localization of nerve growth factor in developing mouse olfactory neurons.

The immunocytochemical localization of nerve growth factor (NGF) in the embryonic mouse has been examined using correlative light and electron microscope procedures. In flat-embedded thick sections, primary sensory neurons of the olfactory pathway were clearly visible by their high level of NGF-like immunoreactivity. When ultrathin sections were examined under the electron microscope, the HRP reaction product present in the nasal epithelium was confined to the cytoplasm of the chemoreceptor cells, including the dendrites projecting into the nasal cavity. The axons projecting to the olfactory bulb and axon bundles within the bulb were also stained specifically for NGF. The reaction product did not appear to be associated with any particular subcellular structure. Neither the columnar supporting cells nor the basal precursor cells showed any evidence of immunoreactivity. No evidence was found for the presence of NGF in cells such as epithelial or glial cells within the immediate environment of the receptor neurons. These first subcellular localization studies indicate the presence of high levels of NGF in neurons not known to be sensitive to the trophic molecule.

Animals↗
PubMed1992

Oxygen and acid chemoreception in the carotid body chemoreceptors.

The carotid bodies are arterial chemoreceptors that are sensitive to blood PO2, PCO2 and pH. They are the origin of reflexes that are crucial for maintaining PCO2 and pH in the internal milieu and for adjusting the O2 supply according to the metabolic needs of the organism in situations of increased demand, such as exercise and while breathing at decreased O2 partial pressures during ascent or when living at high altitude. Chemoreceptor cells of the carotid body transduce the blood-borne stimuli into a neurosecretory response that is dependent on external Ca2+. These cells have an O2-sensitive K+ current that is reversibly inhibited by low PO2. It is proposed that the depolarization produced by inhibition of this K+ current activates Ca2+ channels; Ca2+ influx and neurosecretion follow. The cells have also a potent Na(+)-Ca2+ antiporter that could be responsible for the intracellular Ca2+ rise required to trigger the release of neurotransmitters during high PCO2 or low pH stimulation.

Acids↗
PubMed1975

The ultrastructure of the sensory cells in the chemoreceptor of the ommatophore of Helix pomatia L.

Most of the sensory cells found in the chemoreceptor of the ommatophore of Helix pomatia are typical bipolar cells. The chemoreceptor is deveded by a furrow into two parts; within the ventral subdivision the layer of sensory cell bodiesis thicker than in the dorsal part. According to the differentiations of the apical surface of the dendrites, it is possible to distinguish six different classes: a) dendrites with one cilium and 75 nm thick cytofila (sometimes dendrites of identical appearance posses more than one cilium); b)dendrites with several cilial and 150 nm thick cytofila; c) dendrites with several cilia, 50 nm thick cytofila, and long, striated rootlets; d) dendrites with several cilia bur without cytofila; e) dendrites with 130 nm thick cytofila but without cilia; and f) dendrites with 65 nm thick cytofila but without cilia; dendrites of this class are the only ones with a cytoplasm more electron dense than that of the surrounding supporting cells. All these dendrites are connected to the surrounding supporting cells by terminal bars, each consisting of zonula adhaerens, aonula intermedia and zonula septata. The perikarya of the sensory cells measure approximately 15 mum by 8 mum and enclose 10 mum by 6 mum large nuclei. Axons, originating from these perikarya, extend to the branches of the digital ganglion. In the distal part of this gangloin the axons come into synaptic contact with interneurons, but in our electron micrography it was not possible to coordinate processes and synapses with the corresponding neurons.

Axons↗
PubMed1998

Comparison in vitro of a high- and a low-abundance chemoreceptor of Escherichia coli: similar kinase activation but different methyl-accepting activities.

In Escherichia coli, high-abundance chemoreceptors are present in cellular amounts approximately 10-fold greater than low-abundance chemoreceptors. Cells containing only low-abundance receptors exhibit abnormally low tumble frequencies and do not migrate effectively in spatial gradients. These defects reflect an inherent activity difference between the two receptor classes. We used in vitro assays to investigate this difference. The low-abundance receptor Trg mediated an approximately 100-fold activation of the kinase CheA, only twofold less than activation by the high-abundance receptor Tar. In contrast, Trg was less than 1/20 as active as Tar for in vitro methylation. As observed for high-abundance receptors, kinase activation by Trg varied with the extend of modification at methyl-accepting sites; low methylation corresponded to low kinase activation. Thus, in Trg-only cells, low receptor methylation would result in low kinase activation, correspondingly low content of phospho-CheY, and a decreased dynamic range over which attractant binding could modulate kinase activity. These features could account for the low tumble frequency and inefficient taxis exhibited by Trg-only cells. Thus, the crucial functional difference between the receptor classes is likely to be methyl-accepting activity. We investigated the structural basis for this functional difference by introducing onto the carboxy terminus of Trg a CheR-binding pentapeptide, usually found only at the carboxy termini of high-abundance receptors. This addition enhanced the in vitro methyl-accepting activity of Trg 10-fold.

Bacterial Proteins↗
PubMed1991

Ionic mechanisms for the transduction of acidic stimuli in rabbit carotid body glomus cells.

1. The release of [3H]dopamine (DA) in response to inhibition of the Na+ pump or to intracellular acid load was studied in rabbit carotid bodies (CB) previously incubated with the precursor [3H]tyrosine. The ionic requirements of the release response and the involvement of specific ion transport systems were investigated. 2. Inhibition of the Na+ pump, by incubating the CB with ouabain or in K(+)-free medium, evokes a DA release response which requires the presence of Na+ and Ca2+ in the medium and is insensitive to nisoldipine. This suggests that the response is triggered by entry of external Ca2+ through Na(+)-Ca2+ exchange, a consequence of the increase in intracellular Na+ resulting from inhibition of the pump. 3. Incubation of the CB in medium equilibrated with 20% CO2 at pH 6.6, or in medium containing the protonophore dinitrophenol (DNP) or the weak acid propionate, elicits a DA release response which requires also the presence of Na+ and Ca2+ in the medium and is insensitive to dihydropyridines. 4. Ethylisopropylamiloride (EIPA), an inhibitor of the Na(+)-H+ exchanger, markedly decreases the release response elicited by DNP or propionate in bicarbonate-free medium, but has not any effect in bicarbonate-buffered medium. In the latter condition, the EIPA-insensitive release of DA is inhibited by reducing the HCO3- concentration in the medium to 2 mM or by removal of Cl-, suggesting that in bicarbonate-buffered medium a Na(+)-dependent HCO3(-)-Cl- exchanger is involved in the release response. 5. It is concluded that the release of DA by the chemoreceptor cells in response to acidic stimulation is triggered by entry of external Ca2+ through Na(+)-Ca2+ exchange. This exchange is promoted by the increase of intracellular Na+ that results from the operation of Na(+)-coupled H(+)-extruding mechanisms activated by the acid load.

Acids↗
PubMed2000

Ascending spinal systems in the fish, Prionotus carolinus.

The fin rays of the pectoral fin of the sea robins (teleostei) are specialized chemosensory organs heavily invested with solitary chemoreceptor cells innervated only by spinal nerves. The rostral spinal cord of these animals is marked by accessory spinal lobes which are unique enlargements of the dorsal horn of the rostral spinal segments receiving input from the fin ray nerves. Horseradish peroxidase (HRP) and 1,1;-dioctadecyl-3,3,3', 3'-tetramethylindocarbocyanine perchlorate (diI) were used as anterograde and retrograde tracers to examine the connectivity of these accessory lobes and the associated ascending spinal systems in the sea robin, Prionotus carolinus. The majority of dorsal root fibers terminate within the accessory lobes at or nearby their level of entrance into the spinal cord. A few dorsal root axons turn rostrally in the dorsolateral fasciculus to terminate in the lateral funicular complex situated at the spinomedullary junction. The lateral funicular complex also receives a heavy projection from the ipsilateral accessory lobes. In addition, it contains a few large neurons that project back onto the accessory lobes. Injections of either diI or HRP into the lateral funicular complex label fibers of the medial lemniscus which crosses the midline in the caudal medulla to ascend along the ventral margin of the contralateral rhombencephalon. Within the medulla, fibers leave the medial lemniscus to terminate in the inferior olive and in the ventrolateral medullary reticular formation. Upon reaching the midbrain, the medial lemniscus turns dorsally to terminate heavily in a lateral division of the torus semicircularis, in the ventral optic tectum, and in the lateral subnucleus of the nuc. preglomerulosus of the thalamus. Lesser projections also reach the posterior periventricular portion of the posterior tubercle with a few fibers terminating along the ventral, posterior margin of the ventromedial (VM) nucleus of the thalamus. The restricted projection to the ventral tectum is noteworthy in that this part of the tectum maintains the representation of the ventral visual field, that is, the area in which the fin rays lie. A prominent spinocerebellar system is also evident. Both direct and indirect spinocerebellar fibers can be followed through the dorsolateral fasciculus, with or without relay in the lateral funicular nucleus and terminating in a restricted portion of the granule cell layer of the ipsilateral corpus cerebelli. The similarities in connectivity of the spinal cord between the sea robins and other vertebrates are striking. It is especially notable because sea robins utilize the chemosensory input from the fin rays to localize food in the environment. Thus, although these fish use their spinal chemosense as other fishes use their external taste systems, the spinal chemosense apparently relies on the medial lemniscal system to guide this chemically driven feeding behavior.

Animals↗
PubMed1977

Response of avian intrapulmonary chemoreceptors to venous CO2 and ventilatory gas flow.

Avian intrapulmonary chemoreceptor activity is reduced by increasing airway PCO2 from 0 to 60 torr. Using extracellular electrodes, we recorded discharge of individual intrapulmonary chemoreceptor cell bodies in the left nodose ganglion of the rooster (Gallus domesticus) during unidirectional ventilation of the lungs. All receptors recorded were in the left lung. To vary pulmonary arterial PCO2 independently of ventilation, we ventilated the two lungs separately and supplied the left pulmonary circulation with systemic arterial blood. When the PCO2 in the pulmonary arterial blood was increased, discharge frequency decreased in all 21 receptors studied. Sensitivity to pulmonary arterial PCO2 was similar to sensitivity to airway PCO2. When PCO2 of ventilatory gas was lower than that of pulmonary arterial blood, discharge frequency of the receptor increased when pulmonary blood flow was stopped. Discharge frequency also increased when PCO2 at the receptor site was lowered by increased ventilatory gas flow. We conclude that intrapulmonary chemoreceptors respond to the delivery and removal of CO2 by blood and ventilatory gas. This suggests that the receptors are located within the respiratory gas exchange region of the lung. Because these receptors have a strong inhibitory effect on ventilation, they may serve to (1) adjust minute ventilation to the rate of metabolic CO2 production and (2) to regulate individual breath size.

Animals↗
PubMed2002

Chemosensory stimuli for the walking legs of the crayfish Procambarus clarkii.

Studies of chemoreception in crustaceans have shown that flesh-eating species can detect amino acids, nucleotides and derivatives, and amines, while most herbivorous and omnivorous species are additionally sensitive to carbohydrates. We used extracellular recording techniques to evaluate the effectiveness of a range of nitrogen-containing compounds (mostly amino acids), bile acids, and carbohydrates in stimulating chemoreceptor cells present in the second and third pereopods of the omnivorous crayfish Procambarus clarkii. When applied at a final concentration of approximately 100 microM, effective stimuli were trehalose, leucine, cellobiose, glycine, sucrose, maltose, and ammonium (from most to least effective). The other 17 compounds tested, many chosen because they are potent stimuli for other crustaceans, were ineffective stimuli for P. clarkii. Concentration-response functions were determined for three single cells that were sensitive to ammonium, for five multiunit fibers sensitive to glycine, and for six multiunit fibers sensitive to leucine. Thresholds ranged from 10 nM to 10 micro, functions were generally linear when plotted against the log of the stimulus concentration, and there was little evidence of saturation. While P. clarkii is sensitive to only seven of 24 compounds tested, the compounds that proved stimulatory should serve as cues for location and identification of food items preferred by this omnivorous crustacean.

Animals↗
PubMed1991

The role of cyclic AMP in chemoreception in the rabbit carotid body.

The present study identified physiological factors which influence the generation (and degradation) of cyclic AMP (cAMP) in the arterial chemoreceptor tissue of the mammalian carotid body. Experiments established a 3-way correlation between cAMP generation, neurotransmitter release from chemoreceptor cells, and carotid sinus nerve (CSN) activity. Incubation of carotid bodies in vitro for 10 min in media equilibrated with different low O2 ('hypoxic') gas mixtures (5% O2 or 10% O2, balance N2) elevated basal cAMP levels (100% O2 media) in proportion to the stimulus intensity. Similar experiments using nodose sensory ganglia showed that low O2 stimulation did not alter cAMP levels in this non-chemosensory tissue. However, the adenylate cyclase (AC) activator, forskolin (10 microM), evoked large increases in the cyclic nucleotide content in both carotid bodies and nodose ganglia. After chronic (10 days) CSN denervation or sympathectomy, the basal levels of cAMP in the carotid body were elevated; the cAMP response to low O2 media (stimulus minus control) was increased after CSN denervation but remained unaltered after sympathectomy. The effects of zero Ca2+ media on cAMP generation was examined in order to assess whether feedback from released neurotransmitters acting on known (presynaptic) type I cell receptors could have contributed to the observed changes in cAMP. Basal levels of cAMP were increased 2.8-fold, and the response to hypoxic stimulation was elevated 5-fold, in the absence of extracellular Ca2+. Forskolin (10 microM) did not alter basal release of [3H]-catecholamines ([3H]CA; synthesized from [3H]tyrosine), or resting CSN discharge; however, stimulus-evoked [3H]CA release and CSN discharge were potentiated in the presence of forskolin.(ABSTRACT TRUNCATED AT 250 WORDS)

3,4-Dihydroxyphenylacetic Acid↗
PubMed2001

Nitric oxide and carotid body chemoreception.

Nitric oxide (NO) has been proposed as an inhibitory modulator of carotid body chemosensory responses to hypoxia. It is believed that NO modulates carotid chemoreception by several mechanisms, which include the control of carotid body vascular tone and oxygen delivery and reduction of the excitability of chemoreceptor cells and petrosal sensory neurons. In addition to the well-known inhibitory effect, we found that NO has a dual (dose-dependent) effect on carotid chemoreception depending on the oxygen pressure level. During hypoxia, NO is primarily an inhibitory modulator of carotid chemoreception, while in normoxia NO increased the chemosensory activity. This excitatory effect produced by NO is likely mediated by an impairment of mitochondrial electron transport and oxidative phosphorylation, which increases the chemosensory activity. The recent findings that mitochondria contain an isoform of NO synthase, which produces significant amounts of NO for regulating their own respiration, suggest that NO may be important for the regulation of mitochondrial energy metabolism and oxygen sensing in the CB.

Animals↗
PubMed1998

Fatty acid acylation of dopamine in the carotid body.

In this article, we put forward a hypothesis concerning the assembling and storage of dopamine molecules in the dense-core vesicles of the carotid body chemoreceptor cell. We posit that dopamine molecules are packed and sustained in the vesicular form due to the formation of N-acyldopamine, a condensation product of fatty acid acyl chain and dopamine at the amino group of the latter. N-acyldopamine would then be stored in a micelle-like supramolecular structure formed due to self-association through the hydrophilic dopamine headgroups. This hypothesis may help explain the perennial problem of the role of dopamine in chemoception. It also draws attention to the possibility of the existence of neurotransmitters in the N-acylated form. This could lead to the design of acylated compounds that would play a role of prodrugs slow-releasing active substances by hydrolysis into the desired environment.

Acylation↗
PubMed1999

Sensitivity of the mosquito Aedes aegypti (Culicidae) labral apical chemoreceptors to phagostimulants.

The feeding of Aedes aegypti (L.) on blood and nectar is induced by phagostimulants: adenine nucleotides and sugars respectively. This work examines the responses of the four chemoreceptor cells in the labral apical sensilla to these phagostimulants. The apical chemoreceptors can detect the presence of adenine nucleotides. This part of the response is in good agreement with the gorging behavior. The output of the chemoreceptors cannot distinguish among different adenine nucleotides or among their concentrations (0.01-1 mmol/l), whereas gorging behavior is affected by the identity of adenine nucleotides and by their concentrations. Hence the gorging behavior cannot be driven by the output of these chemoreceptors alone. To the presence of adenine nucleotides Cell 2 was the only cell that responded with high frequencies, while the response of Cell 4 was almost abolished. The response of Cell 2 to ATP depended on the mosquito's physiological state. This dependence accorded well with the gorging behavior; Cell 2 responded with a higher frequency to ATP in the gorging state, than when not in a gorging state. The responses to sucrose and fructose constituted the only case recorded in which all these chemoreceptors failed to respond. This depression of response implies that other chemoreceptors must be present as sugar detectors.

Journal Article↗
PubMed1995

Chemical signals in the marine environment: dispersal, detection, and temporal signal analysis.

Chemical signals connect most of life's processes, including interorganismal relationships. Detection of chemical signals involves not only recognition of a spectrum of unique compounds or mixtures of compounds but also their spatial and temporal distribution. Both spectral and temporal signal processing determine what is a signal and what is background noise. Each animal extracts its unique information from the chemical world and uniquely contributes to it. Lobsters have provided important information on temporal signal processing. Marine chemical signals can be measured with high spatio-temporal resolution giving us a novel view of the lobster's environment. Lobster chemoreceptor cells have flicker fusion frequencies of 4 Hz and can integrate stimuli over 200 ms, closely corresponding to odor sampling behavior with 4-Hz "sniffs." Using this information, spatial odor gradients can be determined from temporal analysis of odor patches typical of turbulent dispersal. Lobsters appear to use this information to locate odor sources. Lobster social behavior depends greatly on chemical signals. Urine carries important information for courtship, dominance, and individual recognition. A novel gland in the nephropore is strategically located to release its products into the urine. Urine, in turn, is injected into the gill current, which jets water 1-2 m ahead of the animal. Lobsters control three different currents that carry chemical signals to and from them. The study of odor dynamics has only just begun. It will be exciting to see how signal dispersal, receptor temporal tuning, neural processing, and animal behavior interact to enhance signals for communication and detection and to reduce signals for chemical camouflage.

Aggression↗
PubMed1999

Modulatory effect of nitric oxide on acetylcholine-induced activation of cat petrosal ganglion neurons in vitro.

The inhibitory effect of nitric oxide (NO) on carotid chemosensory responses to hypoxia has been attributed in part to an antidromic inhibition of chemoreceptor cells activity. However, NO may also modulate the activity of the primary sensory neurons because NO is produced in the soma of these neurons located in the petrosal ganglion. Since a population of petrosal neurons is selectively activated by acetylcholine (ACh), we studied the effects of NO-donor, sodium nitroprusside (SNP), and the NO-synthase inhibitor, Nomega-nitro-l-arginine methyl ester (l-NAME), on the responses evoked in the carotid sinus nerve (CSN) by ACh applied to the petrosal ganglion in vitro. ACh (1 microgram-1 mg) increased the frequency of action potentials recorded from the CSN in a dose-dependent manner. SNP (10-50 microM) reduced the sensibility and amplitude of the CSN response to ACh, although the maximal response appears less affected. The withdrawal of SNP from the superfusion medium increased the sensibility of the responses to ACh. l-NAME (1-2 mM) slightly increased the sensibility of the ACh-induced responses, effect that persisted after l-NAME withdrawal. These results suggest that NO may play a role as modulator in this autonomic primary sensory ganglion.

Acetylcholine↗