Chemical Senses最新文献

The discovery of odorant-binding proteins (OBPs) at the early nineteen eighties raised a lot of interest being the first biochemical components of the olfactory system to be experimentally studied. About 10 years later, the identification of odorant receptors attracted the attention of scientists, leaving OBPs in the background. A generally accepted role as carriers for odorants and pheromones reduced the interest in these soluble proteins, regarded as accessory elements in the process of olfactory transduction. More recently, however, OBPs have received new attention based on (i) the recognition that some proteins of this family can act directly as nonvolatile pheromones, (ii) the possibility of investigating the structures of pheromones in species extinct or difficult to approach adopting the method of reverse chemical ecology, and (iii) the suitability of OBPs and their artificial mutants as sensing elements in electronic olfaction, as well as in other biotechnological applications. In this review, after summarizing the main structural and functional aspects of OBPs and other soluble carrier proteins both in mammals and in arthropods, we focus on their most recent uses and their potential developments.

This review outlines the specific ion channels, taste cell types, downstream signaling, and neural transmission mechanisms involved in the perception of sour and salty tastes. Both of these taste qualities arise from ionic stimuli and so can be detected via ion channels rather than G protein-coupled receptors. Sour taste, triggered by protons in acidic substances such as lemon juice and vinegar, is mediated within taste buds exclusively by type III taste cells. Protons enter the receptor cell through the apically located proton-selective channel OTOP1, thereby directly depolarizing the taste cell and reducing intracellular pH, which may block K+ channels to further amplify the response. Type III cells then release serotonin (5-HT) via conventional chemical synapses to activate nerve fibers. Salt taste involves both type II and type III cells. In a subset of type II cells, low NaCl concentrations, which are appetitive, pass through the apically located, sodium-selective, and amiloride-sensitive epithelial sodium channel. In response, these cells generate action potentials and release ATP through the CALHM1/3 "channel synapse" to stimulate gustatory afferents. High concentrations of NaCl, KCl, and NH4Cl, which are aversive, are detected by a different subset of type II cells and type III cells. Although the depolarizing mechanism for high concentrations of NaCl and KCl remains unidentified, NH4CL is detected by OTOP1 in type III taste receptor cells, and the chloride channel TMC4 may contribute to repolarization of the receptor cells, to enhance their responsivity to the salt stimulus.

The mechanisms involved in the discrimination of basic tastes have been previously studied. However, the mechanisms that differentiate between various substances within the same taste quality remain largely unexplored. This study aimed to determine whether individuals can distinguish 5 different sweet substances and whether this ability can be improved through taste recall training, serving as an entry point for elucidating the underlying mechanism. Forty healthy individuals were divided into 2 groups: a training group (10 males and 10 females) and a control group (10 males and 10 females). The taste recall training involved 5 sweet substances: glucose, fructose, sucrose, maltose, and lactose. Using the filter paper disc method, participants recalled the taste of the 5 sweet substances at a concentration one level below their taste thresholds and then matched the 5 substances. This training was conducted for 3 consecutive days. There were no significant differences in the number of participants, sex, age, body mass index, oral moisture, or baseline taste sensitivity between the training and control groups. The training group showed a significant improvement in the taste thresholds for all 5 sweet substances compared to the control group (glucose: P < 0.001, fructose: P < 0.001, sucrose: P < 0.001, maltose: P < 0.005, lactose: P < 0.001). These findings suggest that taste recall training enhances taste sensitivity for all 5 sweet substances and may improve both taste thresholds and discrimination performance within the same taste quality.

Odor perception is a complex, multimodal experience mainly shaped by the interaction between the olfactory and trigeminal systems. Descriptors such as warm, fresh, or spicy reflect the contribution of chemosensory input from the trigeminal nerve, which adds thermal and tactile dimensions to odor perception. The trigeminal nerve innervates the head, including the nasal cavity; its fibers express several transient receptor potential channels to which odorant molecules can bind. Despite its sensory function and its putative impact on olfactory processing, the chemosensory ability of the trigeminal system has received comparatively little attention. This review examines the molecular and physiological foundations of trigeminal chemosensation, highlighting transient receptor potential channels broad sensitivity, their perceptual roles, and their interactions with the olfactory system. Assessing nasal trigeminal chemosensory function presents several methodological challenges. Here, we explore the tools available for studying the complexity of trigeminal chemosensory encoding ex vivo and in vivo in animal and human models. These techniques have demonstrated that, although the trigeminal and olfactory systems are distinct sensory modalities, they converge at multiple processing stages within the nervous system, including the olfactory epithelium (OE), the olfactory bulb, and other brain regions. In humans, this convergence leads to the activation of overlapping brain regions, resulting in perceptual modulation where information from the trigeminal system enhances or suppresses the response of the olfactory system. As a consequence of this intimate connection, olfactory dysfunction is often accompanied by reduced trigeminal sensitivity. Therefore, we examine the involvement of the trigeminal system in conditions of olfactory dysfunction.

Eating behavior is shaped by genetic, psychological, and physiological factors, with nutrient sensing playing a central role in modulating intake. The tongue, as the primary gustatory organ, initiates this process by influencing hedonic preferences, food choices, and feeding behavior. Recent sensory research has highlighted the potential role of an emerging class of taste modalities known as alimentary tastes. This concept refers to the gustatory detection of compounds that produce weak or subtle taste perceptions but elicit strong postoral effects. While most studies have focused on umami and fat taste in that category, growing interest surrounds newly characterized modalities such as kokumi- and complex carbohydrate-associated tastes. Basic and alimentary taste stimulus influence behavior and physiological processes both pre- and postingestion. Their receptors, present in enteroendocrine cells, detect specific nutrients and regulate gut feedback mechanisms. Emerging research is investigating not only their involvement in metabolic disorders and conditions such as malnutrition, but also their potential as therapeutic targets for modulating appetite, nutrient absorption, and endocrine responses. This narrative review aims to identify and characterize the functions of these postoral receptors along the gastrointestinal tract in the regulation of food intake and to evaluate their therapeutic potential in metabolic conditions such as obesity and type 2 diabetes.

Odors are often considered to be powerful memory cues, yet early olfactory paired-associate (PA) studies suggested that they are less effective than other sensory cues and particularly prone to proactive interference (PI). Research with other modalities indicates semantic similarity increases retroactive interference (RI). Two experiments compared olfactory PA memory to verbal and auditory PA memory, focusing on the role of semantic congruency. In Experiment 1, a mixed design tested the efficiency of odors as a PA cue under semantically congruent versus incongruent conditions. One hundred one participants were randomly assigned to 4 groups, each experiencing one of the following cross-modal pairs: olfactory-visual and verbal-visual (as a control group for olfactory-visual), auditory-visual, and verbal-visual (as a control group for auditory-visual). Replicating prior work, odors were less effective than verbal or auditory cues. However, semantic congruency enhanced performance across modalities, with a greater effect for olfactory PAs. Experiment 2 employed a mixed design to assess PI and RI in olfactory versus verbal PA memory. Thirty-eight participants were randomly assigned to one of two cross-modal pair groups (olfactory-visual and verbal-visual). RI was more pronounced than PI for both modalities, with RI levels increasing when the second pair of associations was semantically congruent, but the first was not. Semantic congruency consistently enhanced olfactory retrieval cues, supporting its role in mitigating interference effects. These findings demonstrate that while odors are less effective associative cues than verbal or auditory stimuli, semantic congruency significantly improves their utility, highlighting the nuanced interplay between modality and memory processes.

We investigated the effects of coding single-nucleotide polymorphisms (SNPs) in bitter taste receptors TAS2R43 and TAS2R46 on their predicted structural stability, cellular functions, and human threshold for bitterness of caffeine. We found differences in the cell surface expression and reaction to caffeine among the haplotypes of TAS2R43 and -46 protein. Ancestral haplotypes of the proteins showed higher response to caffeine than derived haplotypes both for TAS2R43 and -46, which were also predicted to be less structurally stable and showed lower expression at the cell surface membrane. There was a significant difference in human bitter perception of caffeine between people with different TAS2R43 genotypes. Considering the functional differences based on their genotypes and the distribution of the haplotypes in the regions, these SNPs may relate to the sensitivity to several bitter compounds, which correlated with human evolution spread from Africa.

Enzymes exemplify the adaptability of biological systems through their multifunctional roles across tissues. Thus, xenobiotic metabolizing enzymes, traditionally recognized for their contributions to detoxification, biosynthesis, and signaling, also play specialized roles in the nasal cavity, where they encounter volatile compounds on a daily basis. In olfactory tissues, xenobiotic metabolizing enzymes act as odorant metabolizing enzymes, influencing not only volatile xenobiotic clearance but also sensory perception. These enzymes operate within a coordinated network of phase I, II, and III reactions, and are distributed across epithelial and neuronal cell types in both the olfactory and respiratory regions of the nasal cavity. Their expression patterns, activity, and regulatory dynamics suggest that xenobiotic metabolism can modulate olfactory function, with potential implications for toxicity, protection, and sensory modulation. This review first considers the risks posed by airborne xenobiotics and their impact on olfaction, then examines the function, expression, and regulation of odorant metabolizing enzymes, and finally highlights current experimental models and methodological advances that provide insights into xenobiotic and odorant metabolism in the nasal cavity.

Olfactory perception, mediated by G protein-coupled receptors (GPCRs) such as odorant receptors (ORs) and trace amine-associated receptors (TAARs), plays a pivotal role in human health, influencing behaviors like food choices and serving as early biomarkers for neurodegenerative diseases. Despite their importance, olfactory GPCRs are among the least understood members of the GPCR superfamily, and most ORs and TAARs are still orphan receptors. This review provides a comprehensive overview of recent advancements in the structural bioinformatics of olfactory GPCRs. We outline how computational, structure-based strategies have succeeded in identifying novel modulators for olfactory receptors. By discussing recent breakthroughs in GPCR structural biology, such as the first resolved experimental structures of ORs and TAARs, and the transformative impact of AI-driven structure prediction tools for olfactory receptors, this review offers a roadmap for future olfaction pharmacology research.

Early childhood is a critical developmental period for the establishment of flavor preferences that in turn affect food and beverage consumption and health into adulthood. Flavor is a multisensory experience, combining taste and retronasal odor signals. However, while early life development of taste perception has received ample attention, there is limited knowledge of retronasal odor perception in early life. In the present cross-sectional study, we tested the hypothesis that hedonic perception of retronasal smell differs between children and adults. We used video analysis of facial expressions to taste and retronasal odor solutions in children and adults. Children ages 3 to 6 and one of their parents (n = 112 dyads) were asked to sample solutions containing either a taste or an odor compound. A subset of subjects (n = 84 dyads) also explicitly rated each solution on a pictorial liking scale. No differences between the 2 age groups were observed in responses to taste solutions. In contrast, responses to retronasal odor stimuli were less stimulus-specific in children compared with adults. Children showed fewer negative facial expressions to broccoli and pumpkin odors, and more negative facial expressions to apple and mango odors. Similar differences between the 2 age groups were observed in explicit hedonic ratings. These findings support our hypothesis that the hedonic value of retronasal odor components of flavor is not innate but differ between young children and adults.