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PubMed2004

Magnetoreception and its trigeminal mediation in the homing pigeon.

Two conflicting hypotheses compete to explain how a homing pigeon can return to its loft over great distances. One proposes the use of atmospheric odours and the other the Earth's magnetic field in the 'map' step of the 'map and compass' hypothesis of pigeon homing. Although magnetic effects on pigeon orientation provide indirect evidence for a magnetic 'map', numerous conditioning experiments have failed to demonstrate reproducible responses to magnetic fields by pigeons. This has led to suggestions that homing pigeons and other birds have no useful sensitivity to the Earth's magnetic field. Here we demonstrate that homing pigeons (Columba livia) can discriminate between the presence and absence of a magnetic anomaly in a conditioned choice experiment. This discrimination is impaired by attachment of a magnet to the cere, local anaesthesia of the upper beak area, and bilateral section of the ophthalmic branch of the trigeminal nerve, but not of the olfactory nerve. These results suggest that magnetoreception (probably magnetite-based) occurs in the upper beak area of the pigeon. Traditional methods of rendering pigeons anosmic might therefore cause simultaneous impairment of magnetoreception so that future orientation experiments will require independent evaluation of the pigeon's magnetic and olfactory systems.

Animal Migration↗
PubMed2002

Demystifying wine expertise: olfactory threshold, perceptual skill and semantic memory in expert and novice wine judges.

We investigated recognition and identification of wine-relevant odours as a function of domain-specific expertise. Eleven wine experts and 11 wine novices participated in tasks measuring olfactory threshold, odour recognition, odour identification, and consistency of odour naming. Twenty-four wine-relevant odorants were sampled orthonasally by each participant in the semantic (identification; consistency of naming) and episodic (recognition) memory tasks. Results showed superior olfactory recognition by expert wine judges, despite their olfactory sensitivity and bias measures being similar to those of novices. Contrary to predictions based on reports of an association between odour memory and semantic processing, wine experts did not perform better than novices on the verbal memory tasks. Further, ability to recognize odours and ability to name odours were not positively correlated, although the novices' data showed a trend in this direction. The results imply that the source of superior odour recognition in wine experts was not enhanced semantic memory and linguistic capabilities for wine-relevant odours. One interpretation of the data is that wine experts were less susceptible than wine novices to verbal overshadowing. When forced to identify the odorants, experts' superior perceptual skills protected them from verbal interference, whereas novices' generated verbal representations of the odours were emphasized at the expense of the odorant itself. This has implications for training in wine-evaluation skills.

1-Butanol↗
PubMed1997

Odour perception in chronic renal disease.

BACKGROUND: The sense of smell plays an important role in the quality of life. Many studies have shown a declining odour perception in the elderly, as well as in subjects in poor health or nutritional state. Considering the high prevalence of poor nutritional state in renal disease and the importance of odour perception in nutrition and health, the relationship between renal function, nutritional state, and odour perception is explored in this study. METHODS: A total of 101 patients with chronic renal failure participated in the study. Thirty-eight haemodialysis patients (mean age = 64.3 years) were evaluated both before and after dialysis. Sixteen patients on peritoneal dialysis treatment (mean age = 64.0 years), 28 transplanted patients (mean age = 53.5 years, mean creatinine clearance = 64.0 ml/min) and 19 patients with varying degrees of renal insufficiency were also included (mean age = 63.7 years, mean creatinine clearance = 29.5 ml/min). Patients with cognitive deficits or upper respiratory airway diseases were excluded. A validated objective procedure was used to measure odour perception, by determining the detection threshold for isoamyl acetate (banana odour) as the lowest detectable odour concentration. RESULTS: Healthy control persons had significantly lower odour thresholds compared to patients on peritoneal (P = 0.001) and haemodialysis (P = 0.002). No significant difference was observed in odour perception between patients on peritoneal and haemodialysis (P = 0.779) and for patients on haemodialysis before and after a dialysis session. Transplanted patients had significantly better odour perception compared to matched patients on dialysis (P < 0.001). Odour perception of transplanted patients and matched healthy control persons was similar (P = 0.81). In patients with varying degrees of renal insufficiency, including healthy controls and transplanted patients, a significant positive correlation was found between odour perception and creatinine clearance (P = 0.02). A significant negative correlation was found between odour perception and serum concentration of urea (P < 0.001), serum phosphorus (P = 0.022) and protein catabolic rate (P < 0.05). Other parameters measuring nutritional status (albumin, BMI) were not correlated with odour perception. CONCLUSION: Our results show that the ability to smell is severely impaired in patients with chronic renal failure and is related to the degree of renal impairment and the degree of accumulation of uraemic toxins. After renal transplantation, patients have a normal odour perception, indicating the capacity of the olfactory system to recover once the concentration of uraemic toxins remains below a critical threshold. Acute removal of uraemic toxins by dialysis does not correct olfactory disturbances, suggesting a long lasting effect of uraemia on olfactory function.

Adult↗
PubMed1999

A systems perspective on early olfactory coding.

This review critically examines neuronal coding strategies and how they might apply to olfactory processing. Basic notions such as identity, spatial, temporal, and correlation codes are defined and different perspectives are brought to the study of neural codes. Odors as physical stimuli and their processing by the early olfactory system, one or two synapses away from the receptors, are discussed. Finally, the concept of lateral inhibition, as usually understood and applied to odor coding by mitral (or equivalent) cells, is challenged and extended to a broader context, possibly more appropriate for olfactory processing.

Animals↗
PubMed2006

Inheritance of olfactory preferences II. Olfactory receptor neuron responses from Heliothis subflexa x Heliothis virescens hybrid male moths.

Single-cell electrophysiological recordings were obtained from olfactory receptor neurons (ORNs) in sensilla trichodea on male antennae of hybrids formed mainly by crossing female Heliothis subflexa with male Heliothis virescens ('SV hybrids'). We recorded from the A-, B-, and C-type sensilla trichodea, with the latter two types housing ORNs exhibiting response profiles to different pheromone components that we had previously found to be characteristic for each species. For both the B- and the C-type SV hybrid sensilla, most of the ORNs exhibited a spike amplitude and ORN co-compartmentalization within sensilla that more strongly resembled the ORNs of parental H. subflexa rather than those of H. virescens. The overall mean dose-response profiles of the ORNs in hybrid C- and B-type sensilla were intermediate between those of the H. virescens and H. subflexa parental type ORNs. However, not all hybrid ORNs were intermediate in their tuning spectra, but rather ranged from those that closely resembled H. subflexa or H. virescens parental types to those that were intermediate, even on the same antenna. The most noteworthy shift in ORN responsiveness in hybrid males was an overall increase in sensitivity to Z9-14:Ald exhibited by Z9-16:Ald-responsive ORNs. Heightened cross-responsiveness to Z9-14:Ald by hybrid ORNs correlates well with observed behavioral cross-responsiveness of hybrids in which Z9-14:Ald could substitute for Z9-16:Ald in the pheromone blend, a behavior not observed in parental types. The hybrid ORN shifts involving greater sensitivity to Z9- 14:Ald also correlate well with studies of hybrid male antennal lobe interneurons that exhibited a shift toward greater cross-responsiveness to Z9-14:Ald and Z9- 16:Ald. We propose that the differences between parental H. virescens, H. subflexa, and SV hybrid male pheromone ORN responsiveness to Z9-16:Ald and Z9-14:Ald are most logically explained by an increased or decreased co-expression of two different odorant receptors for each of these compounds on the same ORN.

Analysis of Variance↗
PubMed2006

Inheritance of olfactory preferences III. Processing of pheromonal signals in the antennal lobe of Heliothis subflexa x Heliothis virescens hybrid male moths.

Pheromone-responsive olfactory interneurons were studied to determine the extent to which their physiological and morphological properties complemented the behavior and peripheral olfactory neurobiology observed in hybrid male moths created by interbreeding two species of heliothine moth, Heliothis virescens and Heliothis subflexa. Complete recordings were made from a total of 33 neurons, and 16 projection neurons (PNs) were subsequently stained with a fluorescent dye. Stained PNs tuned to pheromonal odorants had dendritic arborizations restricted to one of four olfactory glomeruli that together constituted the macroglomerular complex (MGC). As in parental males, PNs tuned to (Z)-11-hexadecenal always had an arbor in the cumulus, the largest of the MGC glomeruli. Previous neurophysiological investigations revealed that PNs with dendritic arbors restricted to the dorso-medial glomerulus (DM) of the MGC responded specifically to either (Z)-9-tetradecenal (Z9-14:Ald; H. virescens males) or (Z)-9-hexadecenal (Z9-16:Ald; H. subflexa males). Hybrid males, which responded equally well in wind tunnel tests to blends containing either Z9-14:Ald or Z9-16:Ald, had DM PNs that responded to both odorants. PNs specific for a third compound, (Z)-11-hexadecenol, required by hybrid males for behavioral activity were localized to the antero-medial MGC glomerulus (AM). Thus, neuronal activity across the cumulus, DM and AM glomeruli represented an attractive blend in hybrid males. Neurons tuned to (Z)-11-hexadecenyl acetate and Z9-14:Ald were restricted to a fourth, ventro-medial glomerulus. The across-glomerular pattern of activity associated with attractive pheromone blends was most similar to that of H. subflexa males, signifying a dominant effect of H. subflexa genes. These results indicate that the behavioral phenotype of hybrid males can be linked to underlying central olfactory characteristics.

Analysis of Variance↗
PubMed1990

Current concepts in olfaction.

Because of the location of the olfactory epithelium and bulb, the processes involved in olfaction have been difficult to evaluate. However, the recent application of comprehensive nasal endoscopy, reproducible olfactory testing, and molecular biologic techniques to the study of the transduction of olfactory information has elucidated some of the events in odorant perception.

Chronic Disease↗
PubMed1981

Taste preferences and their relation to obesity in dogs and cats.

In the laboratory situation the preferences of dogs and cats for food seem to be relatively uniform. Cats prefer fish and commercial cat food to rats. Dogs prefer beef, pork and lamb to chicken, liver and horsemeat and strongly prefer meat to cereal diets. They prefer canned meat to fresh meat, ground meat to cubed meat and cooked meat to raw meat. Canned or semimoist preparations are preferred to dry ones. Pet dogs have much more variable preferences according to their owner's subjective evaluation. A variety of factors seem to be related in an as yet unknown way to some flavor preferences of pet dogs, i.e. the dog's sex/reproductive status, weight and relationship to owners and the content of the dog's meals. The complicated interaction between (a) a pet's taste, texture and olfactory sensation, (b) its owner's perception of the pet and its preferences and (c) its physical and social environment deserves further investigation. Obesity can result from endocrinological causes such as those following ovariohysterectomy, but most cases appear to be related to owner-induced variables. In a kennel situation most, but not all, dogs can be allowed free access to palatable food without becoming obese.

Animals↗
PubMed1997

Taste- and odor-reactivity in heroin addicts.

Opiates in general, and heroin in particular, are known to induce compulsive drug-seeking and drug-taking behavior. Addiction is accompanied by psychobiological processes which may distort perception of sensory stimuli. Gustatory and olfactory stimuli are hedonically polarized and therefore most appropriate for the assessment of the organism's reactivity to "useful" and "harmful" chemosensory events. Previous studies revealed that psychophysical self-estimates and reflectory facial expressions mirror with comparable reliability the hedonics of the perceived taste and odor sensations. In the present study both cognitive verbal and reflectory facial expressions of a group of: a) heroin addicts were recorded and compared to those of a group of b) detoxified former addicts and to c) a group of matching controls. Results show that all three groups differentiate between pleasant, indifferent and aversive tastes and odors. Active addicts estimated sweet taste and savory smells as being somewhat more pleasant, and bitter and sour tastes and a putrid odor as less unpleasant than did the other two groups. The reflectory facial displays of addicts were less expressive and discriminative than those of the two other groups. Taste- and odor-induced facial displays are known to be controlled primarily by the brainstem. The findings indicate that heroin-addiction affects brain-mechanisms, which mirror taste- and odor-hedonics. Modulation of the phylogenetically ancient, sensory-motor coordinations was found to be of a different pattern than that of the cortically-controlled cognitive reactions.

Adult↗
PubMed2000

The Ras-MAPK pathway is important for olfaction in Caenorhabditis elegans.

The Ras-MAPK (mitogen-activated protein kinase) signal transduction pathway is well known to control cellular proliferation and differentiation in response to extracellular signals, but its other functions are less understood. In Caenorhabditis elegans this pathway regulates several developmental events, such as vulval induction and progression of meiosis, but its function in the nervous system is unknown. Here we report that the Ras-MAPK pathway is involved in olfaction in this organism. Mutational inactivation and hyperactivation of this pathway impairs efficiency of chemotaxis to a set of odorants. Experiments in which let-60 ras was expressed using a heat-shock promoter and a cell-specific promoter show that a normal activity of LET-60 Ras is required in mature olfactory neurons. Application of the odorant isoamylalcohol to wild-type animals leads to the activation of MAP kinase in olfactory neurons within 10 seconds. This induction is dependent on the function of the nucleotide-gated channel TAX-2/TAX-4 and the voltage-activated calcium channel subunit UNC-2. These results suggest a dynamic regulatory role for the Ras-MAPK pathway in perception and transmission of sensory signals in olfactory neurons.

Animals↗
PubMed2004

Informatics approaches to functional MRI odor mapping of the rodent olfactory bulb: OdorMapBuilder and OdorMapDB.

The present study applies informatics tools to aid and extend fMRI analysis of the coding mechanism of neural signals in the rodent olfactory system. Odor stimulation evokes unique spatial patterns of activity in the glomerular layer of the mammalian olfactory bulb (OB). An open-source software program, OdorMap-Builder, has been developed to process the high resolution anatomical and functional MRI images of the OB and to generate single two-dimensional flat maps, called odor maps, that describe the spatial activity patterns in the entire glomerular layer. Odor maps help identify the spatial activity patterns from the tremendous amount of fMRI data and they serve as ideal representation of space coding for the olfactory signals in the OB in response to a given odor stimulation. Based on the fMRI technology, OdorMapBuilder provides comparable odor maps on the intra-subject basis, a significant step towards the detailed analyses of the effects of odor types and/or concentrations. In addition, a new database, OdorMapDB, is developed to provide a repository for the generated odor maps. Web interfaces to the database are provided for the data entry, modification and retrieval. OdorMapDB is based on the EAV/CR (entity-attribute-value with classes and relationships) architecture and it is integrated with two other SenseLab olfactory databases: the olfactory receptor and odor databases. Both OdorMapBuilder and OdorMapDB should serve as useful tools and resources for the field and help facilitate experimental research in understanding the olfactory system and the mechanism for smell perception.

Animals↗
PubMedDate not supplied

Acute effects of 1,1,1-trichloroethane on human olfactory functioning.

BACKGROUND: Animal experiments indicate that 1,1,1-trichloroethane can cause degeneration of the olfactory epithelium. The effects of 1,1,1-trichloroethane on human odor perception still have not been investigated. The goal of this study was to learn more about acute effects of 1,1,1-trichloroethane. METHODS: Twelve healthy, nonsmoking students were exposed to 200 and 20 ppm (control) 1,1,1-trichloroethane in an exposure chamber for 4 hours according to a crossover design. Olfactory functioning was investigated with the Sniffin' Sticks. The test includes the determination of the detection threshold for n-butanol and an odor identification test. RESULTS: After 1 hour of exposure to 200 ppm 1,1,1-trichloroethane, no effects on olfactory functioning were observed. After 4 hours, the olfactory threshold for n-butanol was slightly (p = 0.04) elevated. CONCLUSION: The threshold shift may be caused by different mechanisms, including inflammation of the olfactory mucosa or degeneration of receptor cells.

Administration, Inhalation↗
PubMed2004

Passive perception of odors and semantic circuits.

The sense of smell has been traditionally assumed to be different from other sensory modalities in that odors are encoded perceptually, without a semantic component. Recent findings of improved odor memory upon encoding with verbal cues question this view. Furthermore, familiar odors are easier to remember and discriminate than are unfamiliar ones, and odor familiarity is reported to predict odor naming. To investigate whether familiar odors are processed by different cerebral structures than those that process unfamiliar odors, (15)O H(2)O-positron emission tomography (PET) measurements of cerebral blood flow were carried out in 14 healthy men. The task was passive, birhinal, smelling of familiar odors (FAM), unfamiliar odors (uFAM), and odorless air (AIR). Significant activations (P < 0.05) were calculated using the contrasts FAM-AIR, uFAM-AIR, and FAM-uFAM, and deactivations running these contrasts in the opposite direction. In relation to AIR, both FAM and uFAM activated amygdala, piriform cortex, and parts of anterior cingulate cortex. FAM activated, in addition, left frontal cortex (Brodmann's areas 44,45,47), left parietal cortex incorporating precuneus, and right parahippocampus. Clusters covering parahippocampus and precuneus were observed also in FAM-uFAM. The activation of left frontal cortex and right parahippocampus was positively correlated with familiarity ratings. Smelling of familiar but not unfamiliar odorants seems to engage cerebral circuits mediating memory and language functions, in addition to the engagement of olfactory cortex. Already the most elemental form of odor processing, passive perception thus seems to engage semantic circuits. This is achieved by the ability of odorants to immediately elicit associations and judgments of odor characteristics.

Adult↗
PubMed1995

[Olfactory evoked potentials and contingent negative variation in expert assessment of disordered sense of smell].

Normally, the sense of smell is assessed by means of traditional subjective tests (sniff test, gustatory smell test, and trigeminus test). When results are inconclusive, an objective smell test is indicated. Simultaneously registering olfactory evoked potentials (OEP) and contingent negative variation (CNV) permits evaluation of both odor perception and odor discrimination. We can even objectively assess the false olfactory sensations in parosmia patients who are unable to discriminate between different odors. In this study, the results of 59 patients with olfactory disorders are presented. Head trauma and upper respiratory infections were the most common causes of the patients' complaints. In twelve cases, lack of cooperation and patient unrest prevented us from evaluating the data. In anosmia, the objective results agreed completely with the patient's subjective assessment. In hyposmia and parosmia, the results agreed with the patient's subjective assessment in most cases; here we were able to arrive at a more specific diagnosis in several cases. The objective smell test can be used to supplement subjective methods and thus provide more reliable assessment of olfactory disorders.

Attention↗
PubMed2002

[Odors and olfaction].

In this review, we discuss some of the neural processes involved in the perception of odors that, together with audition and vision, provide essential information for analyzing our surroundings. We shall see how odor detection and learning induce substantial structural and functional changes at the first relay of the olfactory system, i.e., the main olfactory bulb. Among the mechanisms that participate in these modifications is the persistence of a high level of interneuron neurogenesis within the adult olfactory bulb. Our goal is to present some observations related to the neurogenesis that may aid in understanding the neural mechanisms of sensory perception and shed light on the cellular basis of olfactory learning. We summarize the current ideas concerning the molecular mechanisms and organizational strategies used by the olfactory system to transduce, encode, and process information at various levels in the olfactory sensory pathway. Due to space constraints, this review focuses exclusively on the olfactory systems of vertebrates and primarily those of mammals.

Animals↗
PubMed2006

Differential responses to branched and unsaturated aliphatic hydrocarbons in the rat olfactory system.

In an effort to understand mammalian olfactory processing, we have been describing the responses to systematically different odorants in the glomerular layer of the main olfactory bulb of rats. Previously, we demonstrated chemotopically organized and distinct olfactory responses to a homologous series of straight-chained alkanes that consisted of purely hydrocarbon structures, indicating that hydrocarbon chains could serve as molecular features in the combinatorial coding of odorant information. To better understand the processing of hydrocarbon odorants, we now have examined responses to other types of chemical changes in these kinds of molecules, namely, branching and carbon-carbon bond saturation. To this end, we used the [14C]2-deoxyglucose method to determine glomerular responses to a group of eight-carbon branched alkane isomers, unsaturated octenes (double-bonded), and octynes (triple-bonded). In contrast to the differential responses we observed previously for straight-chained alkanes of differing carbon number, the rat olfactory system was not particularly sensitive to these variations in branching and bond saturation. This result was unexpected, given the distinct molecular conformations and property profiles of the odorants. The similarity in activity patterns was paralleled by a similarity in spontaneous perceptual responses measured using a habituation assay. These results demonstrate again the functional relationship between bulbar activity patterns and odor perception. The results further suggest that the olfactory system does not respond equally to all aspects of odorant chemistry, functioning as a specific, rather than a general, chemical analysis system.

Animals↗
PubMed1997

High sulfotransferase activity for phenolic aromatic odorants present in the mouse olfactory organ.

Mouse nasal cytosols show high sulfotransferase (ST) activities toward phenolic aromatic odorants, but have little activities for most alcoholic aromatic odorants. Most ST activities toward the phenolic odorants preferred slightly acidic pH (6.4) and were sensitive to 2,6-dichloro-4-nitrophenol, a specific inhibitor for phenol ST (P-ST) but were not inhibited by triethylamine and tetra-n-butylammonium chloride, which are specific inhibitors for hydroxysteroid ST (HS-ST). These results suggested that P-ST activities are responsible for sulfation of the phenolic odorants. The spectra of the ST activities for these odorants were similar in mouse nasal and liver cytosols, however, nasal cytosols showed much higher ST activity toward cinnamyl alcohol than liver cytosols. This activity preferred higher pH (7.4) compared to the phenolic odorant-ST activities and was inhibited by both types of inhibitors, specific for P-ST and HS-ST. These results appear to indicate the participation of multiple ST isoforms for the sulfation of odorants in mouse nasal cytosols. The existence of P-ST(s) active for the phenolic odorants in olfactory cytosols suggests a role in odorant perception, in particular, in the signal termination process.

Alcohols↗