Protection of olfactory responses from inhibition by ethyl bromoacetate, diethylamine, and other chemically active odorants by certain esters and other compounds

Certain vaporous chemicals (chemically active odorants) arecapable of both stimulating olfactory responses and reactingwith receptors, ion channels, or receptor/ionophore macromoleculesto inhibit olfactory responses. We have studied the physiologicaleffects of several chemically active odorants using electrophysiologicaltechniques to record electroolfactogram (EOG) responses fromthe frog's olfactory mucosa. So far, the most studied agentsare ethyl bromoacetate (EBA), an alkylating agent, and diethylamine(DEA), a compound which is one of the strongest neutral organicbases. Certain odorants, or ‘protectants’, whenpresent before, during, and after exposure of the olfactorymucosa to either EBA or DEA have the property of maintainingolfactory responses which would otherwise be inhibited by exposureto the chemically active odorant alone. Protection from inhibitionby EBA is conferred by the presence of isoamyl acetate and afew closely-related esters, while protection from inhibitionby DEA is produced by the presence of p-dichlorobenzene. Protectionfrom inhibition by DEA is also achieved by lowering the pH ofthe olfactory mucosa through the simultaneous delivery of CO₂which produces carbonic acid. The mechanism of protection byesters and p-dichlorobenzene is unknown, but it seems likelythat these odorants somehow interfere with the access of thechemically active odorant to a site where it would normallyreact. ¹Present address: PSC Box 511, Peterson AFB, Colorado Springs,Colorado 80914, USA. ²Permanent address: Department of Chemistry, New Mexico Instituteof Mining and Technology, Socorro, New Mexico 87801, USA.     

Effect of Nasal Dilators on Perceived Odor Intensity

Subjects wearing nasal dilators rated olfactory stimuli as beingmore intense compared with ratings done without nasal expansion.The results support a perceptual constancy model in olfaction.Chem. Senses 22: 177–180, 1997. ¹Present address: Biology Department, St Lawrence UniversityCanton, NY 13617, USA ²Present address: PO Box 802, Drew University, Madison, NJ 07940,USA     

Electrophysiological Evidence for the Broad Distribution of Specific Odorant Receptor Molecules across the Olfactory Organ of the Channel Catfish

To determine if there is a spatial segregation of responsivenessto odorants within the olfactory epithelium, microelectroderecordings were obtained from small populations of olfactoryreceptor neurons located across different lamellar sensory regionsof the olfactory organ of the channel catfish, lctalurus punctatus.Stimuli included L-alanine, L-methionine, L-arginine hydrochloride,L-glutamic acid, ATP and a mixture of bile salts—odorantspreviously reported to stimulate independent receptor sitesin aquatic species. The peak integrated olfactory receptor responsesat each recording site were standardized to the response toL-alanine. The relative stimulatory effectiveness of the stimuliwas preserved across the 10 olfactory lamellae recording sites.These data support previous molecular biological results ofa broad distribution of receptor neurons that express specificreceptor genes across the olfactory organ of the channel catfish.Chem. Senses 21: 519-527, 1996. ¹Present address: Institute of Cognitive and Computational SciencesGeorgetown University Medical Center, Washington, DC 20007,USA     

Distribution of the stimulatory GTP-binding proteins, Gs and Golf, within olfactory neuroepithelium

Several lines of evidence suggest that, for certain odorants,olfactory signal transduction may be mediated by a stimulatoryG-protein coupled adenylate cyclase cascade. Two stimulatoryG-proteins, G_olf and G_s, are expressed in olfactory tissue.To evaluate their relative contributions to the process of odorantsignal transduction, specific antisera were used to determinethe distribution and relative abundance of G_olf and G_s in ratolfactory neuroepithelium and olfactory sensory cilia. Theseanalyses demonstrate that (1) Golf is far more abundant thanG_s in olfactory neuroepithelium and (2) G_olf is essentiallythe only stimulatory G-protein present in olfactory sensorycilia. ¹Present address: Gene Expression Laboratory, The Salk Institute,PO Box 85800, San Diego, CA 92138, USA     

Odor Perception Phenotypes: Multiple, Specific Hyperosmias to Musks

Olfactory detection thresholds for 11 structurally diverse muskodorants and one non-musk odorant were obtained from 32 subjects.Hierarchical cluster analysis produced four groups of subjects.One group (n = 12) was uniformly sensitive to all musks; another(n = 16) was uniformly insensitive. Two groups of subjects containedotherwise insensitive individuals who were exceptionally sensitiveto cyclopentadecanone and musk xylol (n = 2) and to delta9-hexadecenolactoneand tonalid (n = 2) respectively. We propose that the lattertwo groups are odor perception phenotypes (MSHM1 and MSHM2)that consist of multiple, specific hyperosmias to musk odorants.Chem. Senses 21: 411– 416, 1996. ¹Present address: Synesthetics, Inc., Montclair, NJ 07043, USA     

Isolation and characterization of the cell wall receptor of 14C-malformin in Phaseolus vulgaris L.

¹⁴C-malformin attaches to at least two cell wall receptors inPhaseolus vulgaris. One receptor was extracted with Tris buffer(pH 8.5) and the other with 0.1 N NaOH. In both cases, priortreatment of the walls with wall degrading enzymes (macerase,cellulysin) was required. The two receptors differed with regardto ultrafiltration and gel filtration chromatography. The Tris-extractedreceptor is a protein, probably a glycoprotein, which containshydroxyproline and sulfhydryl groups. Although cuttings nottreated with malformin had Tris-extractable receptor, formationof the receptor appeared to be enhanced by malformin. ¹ Present address: American Cyanamid, P. O. Box 400, Princeton,New Jersey 08540, U. S. A. (Received August 2, 1976; )     

A rapid technique for the determination of RNA and DNA in marine phytoplankton

An adaptation of the ethidium bromide technique for the analysisof nucleic acids is presented for marine phytoplankton. Themethod involves an initial homogenization of cells in phosphatebuffered saline, followed by incubation of subsamples of thecell homogenate in the presence and absence of ribonudease.Quantities of DNA and DNA + RNA in the respective sub-samplesare then determined by reaction with ethidium bromide. An evaluationis made of appropriate levels of bentonite required in the assayto inhibit endogenous cellular ribonucleases. Two nucleoproteindissociating agents, pronase and heparin, are also investigatedfor their capacities to enhance nucleic add fluorescence yield.The final recommended method resulted in maximum measured levelsof RNA and DNA in phytoplankton samples tested. The method canbe rapidly performed, involves a minimum amount of sample manipulation,and yields numbers having a high degree of precision. ¹Current address: School of Fisheries, University of Washington,WH-l0, Seattle, WA 98195, USA. ²Current address: Bigelow Laboratory for Ocean Sciences, WestBoothbay Harbor, ME 04575, USA.     

A simple and flexible device to odorize large stimulation areas

This paper describes a flow dilution olfactometer which allowsthe odorization of large stimulation areas and the easy manipulationof several odorants and/or concentrations. Generation of theodorized air is performed by mixing in two steps the odor vaporcontained in Tedlar bags with a pure air stream flowing continuouslyout of a nozzle. Discrete concentration values are obtainedby using pre-adjusted needle valves to change the vapor flowsampled in the bags. This kind of olfactometer was utilizedto study odor coding in the olfactory bulbs of rats and rabbits.Five Odorants were delivered at concentrations ranging from2 x 10^-4 to 1.5 x 10^-2 of the saturated vapor pressure. Measurementsshowed that lower concentrations can be obtained by fillingthe bags with a more diluted odor vapor. Furthermore, the numberof test odorants can be increased at low cost by increasingthe number of Tedlar bags.     

2-Deoxyglucose analysis of odorant-related activity in the salamander olfactory epithelium

The 2-deoxyglucose technique, which permits quantification oflevels of metabolic activity within neurons, was used to evaluatethe odorant-related activity in the olfactory epithelium ofthe tiger salamander during odorant stimulation. Following pithing,the dorsal wall of the nasal cavity was removed and a largepipette, positioned 1–3 mm above one side of the ventralreceptor sheet, was used to deliver odorants diluted in a purifiedairstream to that epithelium. The contralateral side was exposedto clean air. After a 10 min prestimulation period, the salamanderswere injected with labeled 2-deoxyglucose and further stimulatedwith odorant for 90 min. The right and left epithelia were thendissected out, frozen, sectioned and prepared for routine filmcassette or 6n-the-slide autoradiography. Films were developedafter 10 days and analyzed by densitometry and computer imageprocessing. Slides were developed after 8 weeks and stainedwith cresyl violet. Epithelia exposed to limonene showed ananterior to posterior gradient of increased 2-deoxyglucose activitywhereas control epithelia did not. The epithelial area withthe highest 2-deoxyglucose uptake in animals exposed to amylacetate or limonene were regions which, in previous electrophysiologicalstudies, evidenced greatest activity. Slides analyzed for tritiated2-deoxyglucose uptake showed that the Bowman's glands incorporatedmore labeled metabolite than the epithelial cells. ^* Present address: 4485 Kenneth Drive C-107, Okemos, MI 48864,USA.     

Brain electrical activity mapping: an exploratory study of infant response to odours

This mainly methodological paper describes the novel use ofan established EEG-based brain imaging technique (Brain ElectricalActivity Mapping or BEAM) to explore human infant responsesto odours. The aim of this study was to evaluate BEAM as aninvestigative tool in infant olfaction. A small sample of 3-month-oldinfants was tested in a low ambient odour environment. The infants'cortical responses to a number of proprietary baby-food odourswere recorded. Two experimental hypotheses were addressed. Thefirst concerned relative differences in cortical response beforeand during odour presentation. The second hypothesis statedthat differences would be seen between the various odorants.The overall results supported the first hypothesis. ¹Present address: School of Psychology, University of Birmingham,Birmingham B15 2TT, UK     

Phosphoenolpyruvate Carboxylase of Maize Leaves: an Improved Method for Purification and Reduction of the Inhibitory Effect of Malate by Ethylene Glycol and Bicarbonate

Light-adapted and dark-adapted forms of phosphoenolpyruvatecarboxylase were purified from maize leaves by an improved methodthat included chromatography on Butyl-Toyopearl in the presenceof ethylene glycol. The inhibition by malate was relieved notonly by increasing concentrations of ethylene glycol but alsoby bicarbonate at pH 7.0. ¹Present address: NEOS Central Research Laboratory, 1-1 Ohike-machi,Kosei-cho, Shiga, 520-32 Japan. ²Present address: Asahi Medical Co., Ltd., 4-3400-I Asahimachi,Nobeoka, 882 Japan. ³Present address: Chugai Pharmaceutical Co., Ltd., 1-135 Komakado,Gotemba, 412 Japan.     

PURIFICATION AND PROPERTIES OF SERINE HYDROXYMETHYLTRANSFERASE FROM NICOTIANA RUSTICA L.

Serine hydroxymethyltransferase was partially purified fromNicotiana rustica roots. The pH optimum for the enzyme is 4.0.A requirement for pyridoxal phosphate and a divalent cationwas shown, and the enzyme was inhibited by sulfhydryl reagentsand the reaction is folic acid-dependent. ¹Contribution from the Department of Biochemistry and publishedwith the approval of the Director of Research as Paper No. 2175in the Journal Series ²Present address; Spruance Research Laboratories, E. I. du Pontde Nemours and Company, Inc., Post Office Box 1477, Richmond,Virginia 23212, U.S.A.     

Recent introduction of the planktonic calanoid copepod Sinocalanns doerrii (Centropagidae) from mainland China to the Sacramento-San Joaquin Estuary of California

The planktonic calanoid copepod, Sinocalanus doerrii, a nativeof the rivers of mainland China was found in 1978 in California'sSacramento-San Joaquin Estuary during routine plankton sampling.Previous plankton surveys in 1963 and from 1972 to the presentindicate that the introduction occurred a relativery short timebefore specimens were first caught. The most probable mode ofintroduction is ballast water from Japanese freighters previouslydocking in China. S. doerrii became abundant in the Sacramentoand San Joaquin Rivers in 1979 and may be regarded as well established.Its impact on the native plankton is as yet unknown. ⁴Present address: Department of Biological Science, FloridaState University, Tallahassee, FL 32306, USA. ⁵Present address: 5 Hemingway Street, Branford, CT 06405, USA.     

The influence of water circulation on chlorophyll-turbidity relationships in Lake Okeechobee as determined by remote sensing

The spatial distribution of phytoplankton can be difficult toassess in shallow, productive aquatic systems due to frequentalgal blooms, high turbidity and sediment-resuspension events.We conducted a study to assess the distribution of suspendedparticles in Lake Okeechobee, Florida, utilizing both Landsat(1974–75) or Advanced Very High Resolution Radiometer(AVHRR) (1987) satellite remote sensing. Surface water sampleswere collected by helicopter to determine in situ chlorophyll-aand turbidity levels at 20 stations on four dates in 1974–75and six dates in 1987. Remotely sensed reflectance values agreedwell with in situ particle densities at the 20 in-lake stations(average R²: Landsat = 0.81, AVHRR = 0.53) and independent,synoptic boat mapping of algal blooms (r² = 0.79, P < 0.01).Basin-wide maps of chlorophyll and turbidity, as well as additionalspatial sampling, both indicated that these parameters are notnecessarily coupled in Lake. Our data concur with the hypothesisthat the spatial distributions of chlorophyll and turbidityare shaped by different forces. The highest concentrations ofchlorophyll occurred in the vicinity of tributary nutrient inputsat the lake's perimeter, while turbidity increased towards thecenter of the lake, reflecting predominant water circulationpatterns. ²Present address: Department of Biology & Romberg TiburonEnvironmental Center, San Francisco State University, San Francisco,CA 94132, USA ³Present address: Idaho Division of Environmental Quality, 1420North Hilton, Boise, ID 83706-1260, USA ⁴Present address: 5642 Santiago Circle, Boca Raton, FL 33433,USA     

THE RELATION BETWEEN RED AND BLUE OR FAR-RED LIGHTS IN THE NIGHT-INTERRUPTION OF THE PHOTOPERIODIC TUBERIZATION IN BEGONIA EVANSIANA

Effects of night-interruption on the aerial tuber formationof Begonia evansiana Andr. were investigated. Among coloredlights tested, red light was most effective to reduce the photoperiodicresponse. It inhibited tuberization almost completely at lowintensities. The red lightaction was partially reversed by subsequentblue or far-red irradiation under the 12-hour daylength, andthe relation between the red and the blue or far-red lightswas reversible. No reversal, however, was observed under the8-hour daylength. The inhibitory action of red light remainedunchanged on irradiating with red, blue or far-red light beforethe night periods. ¹Present address: Department of Horticulture, Purdue University,Lafayette, Indiana, USA     

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.     

Induction of a Calcium-dependent Long-term Enhancement of Excitability in the Rat Olfactory Bulb

We have investigated whether a transient increase in extracellularcalcium concentration is able to induce long-term modificationof neuronal excitability in the olfactory bulb. High-calciumartificial cerebrospinal fluid containing picrotoxin (Ca-PTXsolution) was applied locally near the mitral cell layer througha push-pull device for 10 min in anaesthetized rats. Changesin the neuronal excitability were monitored through electrically-evokedfield potentials. Application of the Ca-PTX solution induceda rapid increase in the granule cell response amplitude, whereasmitral/tufted cells response amplitude increased more progressivelyand reached its maximum within a few hours. The increase inmitral/tufted cells response and granule cells response reachedbetween 30 and 100% in experiments which lasted for 4–8h. Pre-application of amino-phosphonovalerate (NMDA receptorblocker) potently reduced both short- and long-term enhancementproduced by the Ca-PTX solution. Neither application of thehigh calcium solution alone nor the picrotoxin solution aloneinduced long-term changes. The results point out the possibleimportance of Ca²⁺ and NMDA receptors in persistent forms ofolfactory bulb plasticity. Relevance of this phenomenon in normalolfactory bulb physiology remains to be examined. Chem. Senses21: 159–168, 1996. ¹Present address: California Institute of Technology, Divisionof Biology 216-76, Pasadena, CA 91125, USA     

The effect of Gymnema sylvestre extracts on the sweetness of eight sweeteners

Although numerous experiments have demonstrated the sweetness-inhibitingeffects of Gymnema sylvestre extracts, no human psychophysicalstudies have been done to quantitatively assess G.sylvestre'seffects across a set of natural and intensive sweeteners. Thepresent study evaluated the sweetness-inhibiting effects ofG.sylvestre extracts on three concentrations each of acesulfameK, aspartame, sodium cyclamate, fructose, glucose, sucrose,stevioside and xylitol. Subjects made sweetness judgements ofthe stimuli following pretreatment with either distilled water,commercial tea or G.sylvestre extracts. Gymnema sylvestre pretreatmentreduced the sweetness of the stimuli by an average of 77% withno evidence for a differential effect across sweeteners. Thepercentage reduction in sweetness was constant across the low,medium and high concentrations of the sweeteners. Kinetic plotsof the data fit the Michelis-Menten model for non-competitiveinhibition, but statistical results did not permit competitiveor uncompetitive mechanisms to be ruled out. A receptor occupancy/blockingmechanism is unlikely. The results support disruption of a moregeneral aspect of sweetness transduction and fit a type of ‘mixed’inhibition involving an effect on the breakdown of the stimulus/receptorcomplex. Inhibition of a later step in a sequential-step transductionsystem and/or a change in the physicochemistry of the environmentof the stimulus/receptor complex are possible. ²Present address: Department of Chemistry, Clark University,Worcester, MA 01610, USA. ³Present address: Department of Psychology, University of Rochester,Rochester, NY 14627, USA     

ODOR DISCRIMINATION BY FROG OLFACTORY RECEPTORS

Single unit activity of olfactory receptors was recorded inthe frog. Seventy per cent of the receptors displayed a restingfrequency lower than 20 spikes min^–1. A 20 ways olfactometerwas designed to automatically stimulate the olfactory epitheliumwith 20 highly purified, simple odorants belonging to severalchemical series, each at a single supraliminal concentration.Twenty three cells failed to respond to any of the 20 stimuli.Following a total of 1160 stimulations delivered to 58 receptorcells, 241 activating and 59 inhibitory responses were recorded,leading to an overall selectivity of 25.8%. Twelve units wereexcited by only one of the 20 chemicals. The activating and inhibitory responses were submitted to mathematicalprocedures (calculation of the Pearson's ‘r’ correlationcoefficient, Benzecri's analysis of correspondences) in orderto determine similarities or proximities between odorants accordingto the response profiles of the receptors. The odour space builtfrom these data was clearly multidimensional. The five primaryaliphatic alcohols of the sample failed to exhibit any specialinter-relationship, except the propanolbutanol pair. Camphorwas quite unrelated to the other chemicals. Six odorants whichpossess in common the aromatic nucleus were found to be relatedby high correlation coefficients; they grouped themselves ina cluster in factor analysis diagrams. They are: benzene, naphthalene,anisole, acetophenone and the almond pair nitrobenzene-benzaldehyde.     

Effects of fluorinated pyrimidines on the growth of excised pea embryos

The effects of some fluorinated pyrimidines on the growth ofexcised pea embryos {Pisum sativum var. Alaska) in sterile culturewere studied. Even the lowest concentrations of the compoundstested inhibited growth in length of the embryos. In order ofdecreasing activity, the compounds tested were : 5-fluorodeoxyuridine,5-fluorodeoxycytidine, 5-fluorouridine, 5-fluoroorotic acidand 5-fluorouracil. Inhibition of growth in length of the rootprimordia was found to be mainly due to inhibition of cell divisionwith no effect on cell elongation. Reversal of fluoropyrimidineinduced inhibition of growth by pyrimidine bases and their relatedmetabolites indicated that the analogues primarily inhibitedDNA synthesis. ¹Part of a thesis submitted by the senior author for the degreeof M.Sc. of the University of Malaya ²Present address: Department of Botany, University College ofWales, Aberystwyth, U.K. (Received October 27, 1969; )