Marine mammal chemoreception

The presence or absence of a chemoreceptive capacity in marine mammals has drawn relatively little attention from the research community outside the Soviet Union. Toothed whales are typically labelled anosmic (lacking a sense of smell) since they do not have the peripheral olfactory structures typically associated with terrestrial mammals. Baleen whales are known to possess reduced olfactory tracts; their olfactory bulbs also may be reduced or absent. Although the neural structures that mediate taste in terrestrial mammals have been reported to be present in both groups of whales, cetaceans have been considered to have a poor sense of taste because typical mammalian taste receptors have been thought to be absent. Soviet researchers, however, recently have reported that gustatory receptors are present on some cetacean tongues and that the tongue of Tursiops truncatus appear to be well innervated. These workers also have been conducting investigations which seem to be aimed at describing a specialized gustatory capability in cetaceans. No experimental work has been reported by Western scientists. Little work has been done by either Western or Soviet researchers with regard to chemoreception among the other orders of marine mammals (Pinnipedia, Carnivora and Sirenia). Pinnipedia are typically labelled microsmatic (having a poor sense of smell); research has been restricted to histological examination of the nasal pathways, and neural anatomy. Sea otters are credited with a keen sense of smell, but no quantitative work has been reported. The chemosensory abilities of Sirenia remain unknown. The tongues of non-cetacean marine mammals have been histologically examined and found to resemble those of terrestrial mammals. No other investigations of gustation in non-cetacean marine mammals have been reported.     

Physics of chemoreception.

Statistical fluctuations limit the precision with which a microorganism can, in a given time T, determine the concentration of a chemoattractant in the surrounding medium. The best a cell can do is to monitor continually the state of occupation of receptors distributed over its surface. For nearly optimum performance only a small fraction of the surface need be specifically adsorbing. The probability that a molecule that has collided with the cell will find a receptor is Ns/(Ns + pi a), if N receptors, each with a binding site of radius s, are evenly distributed over a cell of radius a. There is ample room for many indenpendent systems of specific receptors. The adsorption rate for molecules of moderate size cannot be significantly enhanced by motion of the cell or by stirring of the medium by the cell. The least fractional error attainable in the determination of a concentration c is approximately (TcaD) - 1/2, where D is diffusion constant of the attractant. The number of specific receptors needed to attain such precision is about a/s. Data on bacteriophage absorption, bacterial chemotaxis, and chemotaxis in a cellular slime mold are evaluated. The chemotactic sensitivity of Escherichia coli approaches that of the cell of optimum design.     

Study of the chemoreception in mollusca

Recording of the mollusc osphardium nerve activity revealed the osphardium sensitivity to hyperosmotic pressure, sodium chloride, and aminoacidosis. The osphardium was found to detect quality of the water where the animals were kept. Pont snail osphradium preserves ancestors' multisensority which unites perception of different chemical and physical signals. Patch-clamp method revealed membrane currents in certain ganglia and receptor cells which are sensitive to Na+ and L-aspartate increase in the solution around the osphardium. Inward components of these currents are, probably, of the sodium and/or calcium nature, whereas the outward components--of the potassium one.     

The limiting mechanism in tarsal chemoreception

Rejection thresholds of eight primary alcohols applied to the tarsal chemoreceptors of the blowfly Phormia regina Meigen and the ovipositor of Gryllus assimilis Fab. have been determined. Three different solvents for the alcohols have been used: water, ethylene glycol, and mineral oil. The comparative stimulating effectiveness of the alcohols assumes a different aspect with each different solvent. In oil the range of thresholds from methanol to octanol extends over less than one log unit as compared with the corresponding thresholds in water which extend over four log units. In glycol the thresholds extend over two and one half log units only. When water is employed as a solvent, the line which describes the relationship between threshold concentration and chain length of the compound exhibits a sharp break at or near butanol. No such discontinuity is evident when glycol or oil is employed as solvent. This is offered as evidence supporting the hypothesis that the limiting mechanism in tarsal chemoreception involves a two phase system whereby highly water-soluble compounds gain access to the receptor through an aqueous phase and the larger lipoid-soluble molecules chiefly through a lipoid phase. Additional facts which support this idea are gained from data which show that the inflection in the curve occurs at different points with different species of insects and is conspicuously absent in the case of man. When thresholds in aqueous solutions are converted from molar concentrations to activities, it is clear that the relation of equal physiological effect at equal thermodynamic activities does not apply here. The lower members of the series stimulate at progressively increasing activities up to pentanol and then at progressively decreasing activities. Furthermore, the ratio of water threshold to oil threshold exhibits no obvious agreement with the water/oil partition coefficients determined experimentally. These results indicate either that the limiting process of chemoreception in these insects does not depend upon the establishment of an equilibrium or that some kinetic effect is obscuring an underlying relationship which does so depend.     

Starvation and chemoreception in antarctic benthic invertebrates

Sensitivity (chemoreception) to different amino acids was studied in six invertebrate species: Serolis polita, Glyptonotus antarcticus, Abyssochromene plebs, Waldeckia obesa, Odontaster validus, and Sterechinus neumayeri. The sensitivity was estimated by the changes in basic metabolism (respiration rate). Starvation increased the sensitivity in all the species. The metabolism rates increased in the presence of L-glutamic acid in G. antarcticus, A. plebs, O. validus, and St. neumayeri. The serine and arginine amino acids had a significant impact on the metabolism of the necrophagous species S. polita and W. obesa. The chemical information may be mediated by means of L-glutamic acid via glutamate receptors, which can be blocked by kynurenic acid, as occurs in the experiments with G. antarcticus and A. plebs.     

Haloperidol-induced suppression of carotid chemoreception in vitro

Effects of antagonism of endogenous dopamine with haloperidol on single-unit frequency, interspike interval distribution, and interval serial dependency of the cat sinus nerve were tested using an in vitro carotid body-sinus nerve superfusion technique. A dose dependency of inhibition by haloperidol (0.05-2.0 microgram/ml) was observed. Superfusion with 1-2 microgram/ml haloperidol significantly reduced frequency within 5 min (P less than 0.05) and caused a complete cessation of firing within 25 min in 5 of 10 chemoreceptor units. Frequency recovered to control during drug washout. Acetylcholine (10-micrograms/ml superfusion or 500-micrograms bolus) increased sinus nerve activity under control conditions but not during superfusion with haloperidol. No effect of haloperidol on impulse serial dependency was detected. However, interval distribution was significantly altered by haloperidol in five of six chemoreceptor units. Our results suggest an excitatory role for dopamine in carotid chemoreception.     

Mechanistic events underlying odorant binding protein chemoreception

Odorant binding proteins (OBP's) are small hydrophilic proteins, belonging to the lipocalin family dedicated to bind and transport small hydrophobic ligands. Despite many works, the mechanism of ligand binding, together with the functional role of these proteins remains a topic of debate and little is known at the atomic level. The present work reports a computational study of odorants capture and release by an OBP, using both constrained and unconstrained simulations, giving a glimpse on the molecular mechanism of chemoreception. The residues at the origin of the regulation of the protein door opening are identified and a tyrosine amino-acid together with other nearby residues appear to play a crucial role in allowing this event to occur. The simulations reveal that this tyrosine and the protein's L5 loop are implicated in the ligand contact with the protein and act as an anchoring point for the ligand. The protein structural features required for the ligand entry are highly conserved among many transport proteins, suggesting that this mechanism could somewhat be extended to some members of the larger family of lipocalin.     

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.     

Trigeminal chemoreception in the nasal and oral cavities

Nasal and oral trigeminal chemoreception are discussed witha focus on their functions, responses, and interactions witholfaction and gustation. Trigeminal stimulation elicits a numberof physiological reflexes which are shown to have several possibleeffects on the olfactory and gustatory systems. Based on psychophysicaland electrophysiological data, it is argued that trigeminalchemoreceptors may be stimulated by a wider range of compoundsand concentrations than is generally believed. The molecularstructures which tend to characterize effective trigeminal stimuliare also discussed. It is suggested that the evidence for thediscriminatory ability of trigeminal chemoreceptors is inconclusiveand that this remains a fundamental unanswered question. Finally,the interesting phenomenon of human preference for some initiallyaversive trigeminal stimuli is reviewed. ¹ Present address: Monell Chemical Senses Center, 3500 MarketStreet, Philadelphia, PA 19104. USA.     

Participation of calcium ions in carotid chemoreception]

The changes in calcium accumulation ability of glomus cells membranes under the action of alkaloids, acids and effector stimuli have been studied by fluorimetric chelate probe technique. The reception of these stimuli causes calcium-ions release mainly from the intracellular organoids membranes (mitochondrial and endoplasmatic). These data suggest that calcium-ions act as a messenger between extracellular stimuli and the metabolism of glomus cells. Results obtained provide the evidence of heterogeneity of carotid chemoreception mechanism.     

植物的虫瘿与成瘿昆虫

虫瘿是植物组织遭受昆虫取食或产卵的刺激后,细胞加速分裂和异常分化而长成的畸形瘤状物或突起,它们是昆虫生活的"房子".介绍了虫瘿的形态多样性和形成过程,成瘿昆虫的多样性、生活史、寄生、食性和寄食现象,成瘿昆虫与寄主植物的关系以及人类对虫瘿的利用.     

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 Ca²⁺-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.Abbreviations EGTA ethyleneglycol tetra-acetate - ER endoplasmic reticulum - IBMX isobutyl methylxanthine - I _che index of chemokinesis - Mops 3-[N-morpholino] propanesulfonic acid - PEI phosphoenzyme intermediate - STEN sucrose, TRIS, EDTA, sodium chloride - TCA trichloroacetic acid - TRIS tris[hydroxymethyl] aminomethane