Ghrelin, leptin and adiponectin as possible predictors of the hedonic value of odors

Several lines of evidence point to a close relationship between the hormones of energy homeostasis and the olfactory system. Examples are the localization of leptin and adiponectin receptors in the olfactory system or increased activation of brain regions related to the palatability and the hedonic value of food in response to food pictures after application of ghrelin. In this preliminary study, we tested in 31 subjects (17 male and 14 female) if and to what extent the peripheral blood concentrations of "satiety" hormones, such as leptin, adiponectin, and ghrelin (acyl and total), are correlated with the self-ratings of odor pleasantness and with the objective olfactory and gustatory ability. The hedonic values of some odors were found to be differently rated between donors depending on gender and body weight. The concentrations of leptin, adiponectin and total ghrelin were significantly associated with the hedonic value of pepper black oil, but failed to show significant correlations for 5 other odors tested. Except for a significant association between leptin and odor identification, hormone concentrations were not linked to the abilities of smell and taste. Peripheral adipokines and gut hormones may alter the perception and pleasantness of specific odors, presumably either directly through their receptors in the olfactory system or indirectly through central interfaces between the regulation systems of olfaction, appetite control, memory and motivation.     

Mapping the semantic space for the subjective experience of emotional responses to odors

Two studies were conducted to examine the nature of the verbal labels that describe emotional effects elicited by odors. In Study 1, a list of terms selected for their relevance to describe affective feelings induced by odors was assessed while participants were exposed to a set of odorant samples. The data were submitted to a series of exploratory factor analyses to 1) reduce the set of variables to a smaller set of summary scales and 2) get a preliminary sense of the differentiation of affective feelings elicited by odors. The goal of Study 2 was to replicate the findings of Study 1 with a larger sample of odorant samples and participants and to validate the preliminary model obtained in Study 1 by using confirmatory factor analysis. Overall, the findings point to a structure of affective responses to odors that differs from the classical taxonomies of emotion such as posited by discrete or bidimensional emotion theories. These findings suggest that the subjective affective experiences or feelings induced by odors are structured around a small group of dimensions that reflect the role of olfaction in well-being, social interaction, danger prevention, arousal or relaxation sensations, and conscious recollection of emotional memories.     

Enhancement of retronasal odors by taste

Psychophysical studies of interactions between retronasal olfaction and taste have focused most often on the enhancement of tastes by odors, which has been attributed primarily to a response bias (i.e., halo dumping). Based upon preliminary evidence that retronasal odors could also be enhanced by taste, the present study measured both forms of enhancement using appropriate response categories. In the first experiment, subjects rated taste ("sweet," "sour," "salty," and "bitter") and odor ("other") intensity for aqueous samples of 3 tastants (sucrose, NaCl, and citric acid) and 3 odorants (vanillin, citral, and furaneol), both alone and in taste-odor mixtures. The results showed that sucrose, but not the other taste stimuli, significantly increased the perceived intensity of all 3 odors. Enhancement of tastes by odors was inconsistent and generally weaker than enhancement of odors by sucrose. A second experiment used a flavored beverage and a custard dessert to test whether the findings from the first experiment would hold for the perception of actual foods. Adding sucrose significantly enhanced the intensity of "cherry" and "vanilla" flavors, whereas adding vanillin did not significantly enhance the intensity of sweetness. It is proposed that enhancement of retronasal odors by a sweet stimulus results from an adaptive sensory mechanism that serves to increase the salience of the flavor of nutritive foods.     

Computer modeling of information processing mechanisms in the olfactory system. III. Reproduction of psychophysical phenomena by the olfactory bulb model

Psychophysical phenomena typical of olfaction were reproduced using a computer model of olfactory bulb. The procedure of numerical experiments is described. The model reproduces the following phenomena: fusion of odors, strong and weak odors, suppression of weak odors by strong odors, indemnity of odors, changes in odor with time, consecutive olfactory images, sensibilization, consecutive olfactory constrast, and synergims. It was concluded that computer-assisted experimentation in combination with neurophysiological and psychophysical experiments can considerably increase the efficiency of research of odorants and the olfaction process.     

Effects of olfactory stimuli on arm-reaching duration

The aim of the present study was to investigate the effects of olfactory stimuli on visually guided reaching. In Experiment 1, participants reached toward and grasped either a small (almond/strawberry) or a large (apple/orange) visual target. Any 1 of 4 odors corresponding to the visual stimuli or odorless air was administered before movement initiation. Within the same block of trials, participants smelled 1) an odor associated with an object of a different size than the target, 2) an odor associated with an object of a size equal to that of the target, or 3) odorless air. Results indicated that reaching duration was longer for trials in which the odor "size" and the visual target did not match than when they matched. In Experiment 2, the same procedures were applied but the "no-odor" trials were administered in a separate block to the "odor" trials. Similar results as for Experiment 1 were found. However, in contrast to Experiment 1, the presence of an odor increased the level of alertness resulting in a shortening of reaching duration. We contend that olfactory stimuli have the capacity to elicit motor plans interfering with those programmed for a movement toward a visual stimulus.     

Cortical contributions to olfaction: plasticity and perception

In most sensory systems, the sensory cortex is the place where sensation approaches perception. As described in this review, olfaction is no different. The olfactory system includes both primary and higher order cortical regions. These cortical structures perform computations that take highly analytical afferent input and synthesize it into configural odor objects. Cortical plasticity plays an important role in this synthesis and may underlie olfactory perceptual learning. Olfactory cortex is also involved in odor memory and association of odors with multimodal input and contexts. Finally, the olfactory cortex serves as an important sensory gate, modulating information throughput based on recent experience and behavioral state.     

Olfactory Assays for Mouse Models of Neurodegenerative Disease

In many neurodegenerative diseases and particularly in Parkinson’s disease, deficits in olfaction are reported to occur early in the disease process and may be a useful behavioral marker for early detection. Earlier detection in neurodegenerative disease is a major goal in the field because this is when neuroprotective therapies have the best potential to be effective. Therefore, in preclinical studies testing novel neuroprotective strategies in rodent models of neurodegenerative disease, olfactory assessment could be highly useful in determining therapeutic potential of compounds and translation to the clinic. In the present study we describe a battery of olfactory assays that are useful in measuring olfactory function in mice. The tests presented in this study were chosen because they measure olfaction abilities in mice related to food odors, social odors, and non-social odors. These tests have proven useful in characterizing novel genetic mouse models of Parkinson’s disease as well as in testing potential disease-modifying therapies.     

蚊虫搜寻吸血寄主和产卵行为的调节因子及相关嗅觉机理

嗅觉在蚊虫的吸血寄主搜寻、产卵和糖源搜寻行为中起决定作用,而在交配行为中的作用并不清楚。本文系统全面地综述了近20年来蚊虫化学生态学和嗅觉识别的分子机理的研究。蚊虫的触角、下颚须和口喙上的嗅觉感器感觉环境中释放的各种挥发性化合物。气味分子与嗅觉气味结合蛋白和气味受体的结合所启动的一系列生化反应产生神经动作电位。蚊虫嗅觉神经元编码气味中化合物的组成、浓度及其暂时瞬间的浓度变化和空间分布。吸血前后神经元的活性在数量和质量上有变化,反映了蚊虫在搜寻吸血寄主和产卵行为上的调节。在吸血寄主搜寻中,人体和动物释放的二氧化碳、乳酸以及其他气味协同引诱蚊虫向目标气味源定向飞行,最后找到吸血寄主。而成熟产卵雌蚊是利用产卵场所释放的腐烂气味寻找适宜的产卵场所,一些蚊虫卵、幼虫或蛹分泌的产卵信息素引诱和刺激雌蚊产卵,并与产卵生境气味起协同作用。植物气味尤其是花香味引诱蚊虫找到蜜源。驱避剂也是直接或间接通过嗅觉起作用,一些驱蚊剂由于阻断嗅觉反应而抑制蚊虫的定向飞行。从植物、动物或人体以及产卵场所释放的气味中有望找到有效的引诱和驱避化合物。对蚊虫嗅觉识别机理的认识将使我们开发出有效的蚊虫诱捕技术,进而应用于种群监测和控制。     

Brain Processing of Biologically Relevant Odors in the Awake Rat,as Revealed by Manganese-Enhanced MRI

Background

So far, an overall view of olfactory structures activated by natural biologically relevant odors in the awake rat is not available. Manganese-enhanced MRI (MEMRI) is appropriate for this purpose. While MEMRI has been used for anatomical labeling of olfactory pathways, functional imaging analyses have not yet been performed beyond the olfactory bulb. Here, we have used MEMRI for functional imaging of rat central olfactory structures and for comparing activation maps obtained with odors conveying different biological messages.

Methodology/Principal Findings

Odors of male fox feces and of chocolate flavored cereals were used to stimulate conscious rats previously treated by intranasal instillation of manganese (Mn). MEMRI activation maps showed Mn enhancement all along the primary olfactory cortex. Mn enhancement elicited by male fox feces odor and to a lesser extent that elicited by chocolate odor, differed from that elicited by deodorized air. This result was partly confirmed by c-Fos immunohistochemistry in the piriform cortex.

Conclusion/Significance

By providing an overall image of brain structures activated in awake rats by odorous stimulation, and by showing that Mn enhancement is differently sensitive to different stimulating odors, the present results demonstrate the interest of MEMRI for functional studies of olfaction in the primary olfactory cortex of laboratory small animals, under conditions close to natural perception. Finally, the factors that may cause the variability of the MEMRI signal in response to different odor are discussed.     

果蝇嗅觉分子机理研究进展

黑腹果蝇Drosophila melanogaster是生物学研究的重要模式生物,也是探索研究生物体嗅觉奥秘的理想材料。近年来,由于分子生物学技术在神经科学领域的广泛应用,黑腹果蝇嗅觉机理研究取得了许多重大突破, 对气味分子受体及其识别机理、 嗅觉神经电信号的产生和传递、嗅觉信息的加工、编码以及记忆等方面都有了深入的了解。研究表明, 果蝇约1 300个嗅神经元(olfactory receptor neurons, ORNs)共表达62种不同的气味受体蛋白（olfactory receptor proteins, ORs）, 用以检测和识别其所感受的所有化学气味分子。许多OR所识别的气味分子配体已鉴定出来,普通的气味（如水果的气味）由数种不同的OR组合来识别,而信息素（pheromone）分子则由单种特定的OR来检测。气味信息在嗅神经元内转换成神经电信号,嗅觉电信号沿嗅神经元的轴突传递到触角叶, 再经投射神经元（projection neurons, PNs）将信息送至高级中枢如蘑菇体（mushroom body, MB）和侧角（lateral horn, LH）,最终引发行为反应。在黑腹果蝇嗅觉信息传递通路中,某些蛋白如Dock,N-cadherin,Fruitless等起着重要作用,缺失这些蛋白会导致嗅觉异常。本文对这些研究进展作一综述。     

Investigation of breathing parameters during odor perception and olfactory imagery

Compared with visual and auditory imagery, little is known aboutolfactory imagery. There is evidence that respiration may bealtered by both olfactory perception and olfactory imagery.In order to investigate this relationship, breathing parameters(respiratory minute volume, respiratory amplitude, and breathingrate) in human subjects during olfactory perception and olfactoryimagery were investigated. Fifty-six subjects having normalolfactory function were tested. Nasal respiration was measuredusing a respiratory pressure sensor. Using an experimental blockdesign, we alternately presented odors or asked the subjectsto imagine a given smell. Four different pleasant odors wereused: banana, rose, coffee, and lemon odor. We detected a significantincrease in respiratory minute volume between olfactory perceptionand the baseline condition as well as between olfactory imageryand baseline condition. Additionally we found significant differencesin the respiratory amplitude between imagery and baseline conditionand between odor and imagery condition. Differences in the breathingrate between olfactory perception, olfactory imagery, and baselinewere not statistically significant. We conclude from our resultsthat olfactory perception and olfactory imagery both have effectson the human respiratory profile and that these effects arebased on a common underlying mechanism.     

Olfaction and neurogenesis in the olfactory epithelium

Anosmia was experimentally produced in strain C57BL/6 laboratory mice by treatment with 1% zinc sulfate solution. Structural and functional changes taking place in the olfactory epithelium were investigated during this process and during reinstatement of olfaction. Isoamyl acetate, butyl acetate, and substances present in murine urine were used as olfactory stimuli. Response to these odorants was found to recover from zinc sulfate action at different rates. The highest (both relative and absolute) daily rise in amplitude response was that induced by isoamyl acetate and butyl acetate and lowest in the case of odors of biological origin. Response to olfactory stimuli recovered most rapidly in the areas of the epithelium where maximum response to the same stimuli had been seen in intact animals."Biopharmautomatica" Combined Research and Production Unit, Gor'kii. Translated from Neirofiziologiya, Vol. 22, No. 4, pp. 500–506, July–August, 1990.     

Olfactory receptor gene family evolution in stickleback and medaka fishes

Interaction of olfactory receptor (OR) genes with environmental odors is regarded as the first step of olfaction. In this study, OR genes of two fish, medaka (Oryzias latipes) and stickleback (Gasterosteus aculeatus), were identified and an evolutional analysis was conducted. The selection pressure of different TM regions and complete coding region were compared. Three TM regions (TM4, TM5 and TM6) were found to have higher average Ka/Ks values, which might be partly caused by positive selection as suggested by subsequent positive selection analysis. Further analysis showed that many PTSs overlap, or are adjacent to previously deduced binding sites in mammals. These results support the hypothesis that binding sites of fish OR genes may evolved under positive selection.     

Cross-modal interactions between olfaction and touch

We report two experiments designed to investigate the nature of any cross-modal interactions between olfactory and tactile information processing. In Experiment 1, we assessed the influence of olfactory cues on the tactile perception of fabric softness using computer-controlled stimulus presentation. The results showed that participants rated fabric swatches as feeling significantly softer when presented with a lemon odor than when presented with an animal-like odor, demonstrating that olfactory cues can modulate tactile perception. In Experiment 2, we assessed whether this modulatory effect varied as a function of the particular odors being used and/or of the spatial coincidence between the olfactory and tactile stimuli. The results replicated those reported in Experiment 1 thus further supporting the claim that people's rating of tactile stimuli can be modulated by the presence of an odor. Taken together, the results of the two experiments reported here support the existence of a cross-modal interaction between olfaction and touch.     

Measures of human olfactory perception during pregnancy

Although considerable anecdotal evidence suggests that pregnancy affects olfactory sensitivity, scientific evidence is limited and inconclusive. Whereas hedonic ratings are affected by pregnancy, odor identification is not. The aim of the current study was to examine odor perception in women across pregnancy and in the postpartum period. One hundred nonsmoking women who were pregnant, postpartum, or had never been pregnant were tested on the University of Pennsylvania Smell Identification Test (UPSIT). Intensity ratings and scratch patterns were collected as potential indicators of sensitivity, and participants rated the odors' pleasantness. Participants also rated their own sense of smell. Mean UPSIT scores did not differ significantly across groups indicating no difference in odor identification. Trends in planned comparisons suggested that in the first trimester, odors were rated as more intense and less pleasant. In the first trimester, women scratched the odor strips significantly fewer times. Consistent with previous reports, 90% of pregnant women reported that specific odors smelled less pleasant and 60% reported that some odors smelled more pleasant. Although nearly two-thirds of pregnant women rated their olfactory sensitivity to be enhanced during pregnancy and overall pregnant women's self-rated olfactory sensitivity was higher than controls', self-ratings were not correlated with UPSIT scores nor odor intensity ratings. These results suggest that these and previous findings may reflect the fact that the effect of pregnancy on olfaction is small and inconsistent.     

Evidence of odor priming: edibility judgements are primed differently between the hemispheres

In olfaction, there is only weak evidence of repetition priming. Repetition priming was therefore investigated in two experiments using birhinal presentation of odors at study and monorhinal at test. Experiment 1 demonstrated repetition priming for repeated judgements of edibility in terms of response latency, but not in terms of correctness. No differences were found between the hemispheres (nostrils). Experiment 2 utilized a slightly different design, in which identity of odors was studied and judgement of edibility was tested. This time, only the right hemisphere (RH) was associated with priming. This persistence of RH priming should be seen in the light of a general tendency for superiority of the left hemisphere for correctly judging edibility. It is concluded that the olfactory system benefits from previous exposure/processing just as do vision, audition and touch. In line with previous research in vision, it is suggested that RH priming may be more associated with perceptual priming and left-hemisphere (LH) priming with conceptual priming.     

Combinatorial receptor codes for odors

The discriminatory capacity of the mammalian olfactory system is such that thousands of volatile chemicals are perceived as having distinct odors. Here we used a combination of calcium imaging and single-cell RT-PCR to identify odorant receptors (ORs) for odorants with related structures but varied odors. We found that one OR recognizes multiple odorants and that one odorant is recognized by multiple ORs, but that different odorants are recognized by different combinations of ORs. Thus, the olfactory system uses a combinatorial receptor coding scheme to encode odor identities. Our studies also indicate that slight alterations in an odorant, or a change in its concentration, can change its "code," potentially explaining how such changes can alter perceived odor quality.     

Perceptual blending in odor mixtures depends on the nature of odorants and human olfactory expertise

Our olfactory system is confronted with complex mixtures of odorants, often recognized as single entities due to odor blending (e.g., coffee). In contrast, we are also able to discriminate odors from complex mixtures (e.g., off-odors). Therefore, the olfactory system is able to engage either configural or elemental processes when confronted with mixtures. However, the rules that govern the involvement of these processes during odor perception remain poorly understood. In our first experiment, we examined whether simple odorant mixtures (binary/ternary) could elicit configural perception. Twenty untrained subjects were asked to evaluate the odor typicality of mixtures and their constituents. The results revealed a significant increase in odor typicality in some but not all mixtures as compared with the single components, which suggest that perceptual odor blending can occur only in specific mixtures (configural processing). In our second experiment, we tested the hypothesis that general olfactory expertise can improve elemental perception of mixtures. Thirty-two trained subjects evaluated the odor typicality of the stimuli presented during the first experiment, and their responses were compared with those obtained from the untrained panelists. The results support the idea that general training with odors increases the elemental perception of binary and ternary blending mixtures.     

Olfactory networks: from sensation to perception

Olfactory networks, comprised of sensory neurons and interneurons, detect and process changes in the chemical environment to drive animal behavior. Recent studies combining genetics with behavioral analyses and imaging in worms, flies and mice have revealed new insights into the mechanisms of olfaction. In this discussion, we focus on three interesting findings. First, sensory neuron responses to odor are modulated by neuropeptides. This modulation might serve to extend the range of responses of the sensory neurons and also to integrate internal state information into the chemosensory circuit. Second, genetic tracing studies in mice and flies have shown that the first layer of connections in chemosensory circuits from olfactory epithelium to the glomeruli are stereotyped, while the subsequent connections to higher order sensory processing regions are not. Distributed connectivity to the higher order sensory processing regions has profound implications for how odors are represented in those regions. Third, recent work has revealed that odors are surprisingly sparsely represented in the piriform cortex. The sparse coding in the higher brain centers implies a much greater role for experience and learning in mediating responses to olfactory cues. Analyzing olfactory network function in various species provides us with fascinating clues about how sensory information is acquired, processed and represented at multiple levels within the nervous system.     

Rasagiline Ameliorates Olfactory Deficits in an Alpha-Synuclein Mouse Model of Parkinson's Disease

Impaired olfaction is an early pre-motor symptom of Parkinson''s disease. The neuropathology underlying olfactory dysfunction in Parkinson''s disease is unknown, however α-synuclein accumulation/aggregation and altered neurogenesis might play a role. We characterized olfactory deficits in a transgenic mouse model of Parkinson''s disease expressing human wild-type α-synuclein under the control of the mouse α-synuclein promoter. Preliminary clinical observations suggest that rasagiline, a monoamine oxidase-B inhibitor, improves olfaction in Parkinson''s disease. We therefore examined whether rasagiline ameliorates olfactory deficits in this Parkinson''s disease model and investigated the role of olfactory bulb neurogenesis. α-Synuclein mice were progressively impaired in their ability to detect odors, to discriminate between odors, and exhibited alterations in short-term olfactory memory. Rasagiline treatment rescued odor detection and odor discrimination abilities. However, rasagiline did not affect short-term olfactory memory. Finally, olfactory changes were not coupled to alterations in olfactory bulb neurogenesis. We conclude that rasagiline reverses select olfactory deficits in a transgenic mouse model of Parkinson''s disease. The findings correlate with preliminary clinical observations suggesting that rasagiline ameliorates olfactory deficits in Parkinson''s disease.