Chemoreceptors studies

If the allelochemical is hydrophylic, it cannot enter into the cell and act from outside by binding with chemoreceptors. The compounds from allelopathically active plants may serve as chemosignals and their signalling occurs via alternative pathways (i) Chemoreceptor (sensors) — transducers (G-proteins) —> secondary messengers (Ca2+, cyclic AMP or GMP, inositol triphospate, etc) —> organelles or (ii) Chemoreceptor (sensors) —> ion channels —> action potential organelles, or (iii) Chemoreceptor (sensors) —> ion channels —> cytoskeleton— organelles (Roshchina, 2005 a). What is the effect of acted allelochemical on the pathways, could be analysed to study the effects of substances on separate sites of the transduction chain. 

Results of in vitro studies suggest an interaction between calcium ions and cyanide in cardiovascular effects (Allen and Smith 1985 Robinson et al. 1985a). It has been demonstrated that exposure to cyanide in metabolically depleted ferret papillary muscle eventually results in elevated intracellular calcium levels, but only after a substantial contracture develops (Allen and Smith 1985). The authors proposed that intracellular calcium may precipitate cell damage and arrhythmias. The mechanism by which calcium levels are raised was not determined. Franchini and Krieger (1993) produced selective denervation of the aortic and carotid bifurcation areas, and confirmed the carotid body chemoreceptor origin of cardiovascular, respiratory and certain behavioral responses to cyanide in rats. Bradycardia and hyperventilation induced by cyanide are typical responses evoked by carotid body chemoreceptor stimulation (Franchini and Krieger 1993). 

The vomeronasal system, also known as the accessory olfactory system, consists of chemoreceptors, organized into the VNO, the vomeronasal nerve, its terminal, the accessory olfactory bulb, and more central pathways. First described by Jacobson in 1811, the VNO has been studied intensely. We now know how stimuli reach it and what behaviors it mediates. The VNO occurs in amphibians, reptiles, and mammals. Among mammals, it is best developed in marsupials and monotremes. In birds it only appears during embryogenesis. The VNO and its function are best known for squamate reptiles, particularly snakes, and rodents and ungulates among the mammals. 

P americana is one of just a few species of insects in which both peripheral and central olfactory processing have been studied. In contrast to many short-lived lepidopterans, in which the male antenna is highly specialized for sex pheromone reception, the antennae of male cockroaches contain numerous food-responsive sensilla. In addition to olfactory sensilla, the antennae also house mechano-, hygro-and thermoreceptors, as well as contact chemoreceptors (Schaller, 1978 review Boeckh et al., 1984). Extensive ultrastructural and electrophysiological evidence has demonstrated that morphologically defined sensillum types house receptor cells of specific functional types (Sass, 1976, 1978, 1983 Schaller, 1978 Selzer, 1981, 1984 review Boeckh and Ernst, 1987). Boeckh and Ernst (1987) defined 25 types of cell according to their odor spectra, but of the 65 500 chemo- and mechanosensory sensilla on the antenna of adult male P. americana, an estimated 37 000 house cells that respond to periplanone-A and periplanone-B. 

Ache and coworkers demonstrated that both cyclic nucleotides and inositol phosphates mediate the transduction of environmental chemical signals by the olfactory neurons of P. argus.62 65 Both biochemical and molecular biological techniques have shown that the receptor cells contain various G-protein subunits that would be necessary for signal detection by G-protein-associated chemoreceptors.48 49 66-69 In combination with electrophysiological studies,... 

Electrophysiological studies of the smell and taste systems of fish have likewise demonstrated chemoreceptor cells that are responsive, with varying degrees of specificity, to the amino acids known to elicit feeding behavior.73 75 In addition, a number of fish have receptor cells that respond to bile acids, amphipathic steroid compounds that are used as digestive detergents and that can be released into the environment in substantial quantities. Responses can exhibit both exquisite specificity for the structure of a bile acid, and extreme sensitivity, as best exemplified by the sea lamprey.76 77... 

Hodgson, E.S. and Roeder, K.D. (1956). Electrophysiological studies of arthropod chemoreception. 1. General properties of the labellar chemoreceptors of diptera../. 

Vallet, A.-M., Marion-Poll, F. and Trabalon, M. (1998). Preliminary electrophysiological study of the contact chemoreceptors in a spider. C. R. Acad. Sc. Paris, serie III, 321, 463—469. 

The second type of study which has contributed to our understanding of the functional properties of oral chemoreceptor systems is human psychophysics, where verbal reports are taken on the taste properties of food and beverages and their chemical constituents. It is often possible for an individual to break a flavor complex down into a variety of distinguisable sensations. These sensations are end products of neural processing that are available to consciousness. Any natural food is of complex chemical composition and thus activates a wide variety of oral and nasal chemoreceptors. These flavor sensations may arise entirely from the oral cavity or require both oral and nasal stimulation. 

Studies on human taste sensations confirm and extend our understanding of the types of chemical signals measured by these oral chemoreceptor systems. There are, for instance, several distinct sensations elicited by chemical stimulation of fungiform papillae innervated by the geniculate ganglion, indicating that a neural functional complexity similar to that described above for... 

Some trichothecene-induced effects may be due to neurotransmitter alteration in the central nervous system. Emesis or vomiting, which occurs with many of the trichothecenes when given at high doses, has been attributed to the stimulation of the chemoreceptor trigger zone in the area postrema of the medulla oblongata. However, studies with T-2 toxin in cats indicated that other mechanisms, such as the neural afferent pathways from the abdomen, implicated in radiation-induced emesis, may also be involved (Borison and Goodheart, 1989). DON alters serotonin activity in the central nervous system of swine which is important in... 

His studies also revealed that after a period of treatment, some trypanosomes or spirochaetes became resistant to the administered drugs, presumably because their chemoreceptors became less specific for the drug. The adverse effects elicited in the patient thus increased as the antimicrobial effect decreased. One solution to this problem was to administer mixtures of drugs with affinities for different classes of chemoreceptors. In this way, smaller quantities of the drugs could be used, and there was an increased chance that the microorganism would be completely eliminated before it had time to become resistant. Combination chemotherapy, the mainstay of modem cancer chemotherapy, arose from experiments of this kind. 

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