Chemical Senses最新文献

Olfaction is involved in detecting, identifying, and discriminating dietary fat within foods, yet the underlying neural mechanisms remain uncharted. Our functional magnetic resonance imaging (fMRI) study investigated the neural correlates of olfactory fat perception and their association with discrimination ability in a complex food matrix. We measured brain activation resulting from orthonasal exposure to an ecologically relevant fat-related odor source-dairy milk, manipulated to contain 0%, 3.5%, or 14% fat. Twenty-six healthy, normosmic adults underwent olfactory fat content discrimination testing, followed by an fMRI task during which the 3 odor stimuli were delivered via an olfactometer (25 times/fat level) and rated on perceived intensity and liking. Participants discriminated between all fat levels, with fat level influencing perceived odor intensity and liking. These perceptual differences, however, were not reflected in differential brain activation. Brain activation differences were observed only when comparing odor exposure with no exposure. Specifically, in response to any odor, activation occurred in the anterior part of the supplementary motor area (SMA) while deactivating parts of the hippocampus, putamen, superior temporal gyrus, anterior cingulate cortex, insula, and posterior part of the SMA. Exposure to the 0% fat odor also activated the thalamus. No associations were found between perceived intensity and liking and neural responses. Results reaffirm the human ability to distinguish food fat content using solely olfactory cues and reveal a divergence between sensory perception and neural processing. Subsequent research should replicate and extend these findings onto retronasal fat perception while also examining potential effects of hunger, genetics, and dietary habits.

Olfactory dysfunction resulting from COVID-19 has imparted a lasting impact on olfaction among the general public, including pregnant women contracting SARS-CoV-2 infection. While olfactory dysfunction can impact physical, mental, and psychosocial well-being, there has been little research on olfaction during pregnancy and postpartum, nor the impact of SARS-CoV-2 infection on olfaction while pregnant. Therefore, the primary study aims are to evaluate olfaction in the postpartum period and determine the impact of antecedent SARS-CoV-2 infection. We recruited two cohorts of postpartum women, those with a history of SARS-CoV-2 infection before or during pregnancy (COVID cohort; n = 109) and those without (non-COVID cohort; n = 226), and evaluated their olfaction during the postpartum period by administering the University of Pennsylvania Smell Identification Test. Participants were queried about demographics, past SARS-CoV-2 infections, self-reported sense of smell (both in overall ability to smell and for the presence of qualitative smell issues such as parosmia and phantosmia), and perceived cause of smell loss, if any. We found significantly fewer postpartum women with normosmia capabilities in both COVID (27%) and non-COVID (46%) cohorts compared to normative data for aged-matched (30 to 39 years) women (83%). Women in the non-COVID cohort had significantly higher UPSIT scores and mean subjective olfaction ratings than those in the COVID cohort (95% CI [0.77,2.41] and 95% CI [-0.83,7.34], respectively). This study reflects the largest published cohort of postpartum women evaluated for olfactory function with standardized psychophysical testing. Our findings suggest both postpartum and SARS-CoV-2 infection are associated with diminished smell function.

Millions of people in the United States experience a reduced or distorted ability to smell or taste. Chemosensory disorders such as anosmia (the inability to smell), parosmia (distorted smell), or dysgeusia (altered taste) have major impacts on health and quality of life including difficulty sensing dangers such as fire or spoilage, a diminished palatability of food and drink that can negatively influence diet and nutrition, feelings of social isolation, and an increased incidence of frailty, anxiety, and depression. Smell or taste dysfunction can also be symptoms of other health issues, including sinonasal disease, cancer, or neurodegenerative disease. Aging adults are disproportionately affected. However, smell and taste function are not regularly assessed as a part of routine healthcare despite their prevalence and impact. This is a lost opportunity, as early detection of a chemosensory disorder would enable patients to obtain needed validation, education and support for their health challenge, could direct both patient and provider to treatment options, and may suggest underlying health issues that should be addressed. To better understand the current barriers to including chemosensory testing as a regular component of health care and to identify opportunities to overcome those barriers, the conference "Towards Universal Chemosensory Testing" was convened on November 5-7, 2023, in Philadelphia, PA. This conference brought together scientists, clinicians, patients, and other experts to discuss these issues and identify collective ways to overcome barriers to testing. This white paper-which is focused primarily on the US healthcare system-is the result of those discussions.

Contrary to all other sensory systems, olfactory information is processed predominantly ipsilaterally. Furthermore, odor localization, based on inter-nostril differences, is usually not possible under controlled conditions. These two observations suggest information exchange between both cerebral hemispheres in the olfactory system, although the exact anatomical substrate remains unknown. This study aimed to identify the anatomical structures necessary for odor localization, with a particular focus on the role of interhemispheric communication. We assessed the ability to localize pure olfactory and mixed olfactory/trigeminal stimuli in 6 participants with structural interhemispheric deficits (including surgical transection or agenesis of the corpus callosum (CC) and agenesis of the CC and anterior commissure (AC, one case)) and compared their performance to 46 healthy controls. Of the six participants with structural interhemispheric deficits, three were unable to localize either stimulus. Two participants performed significantly better than chance for both pure and mixed stimuli, while one participant exhibited the typical localization pattern observed in most controls-accurate localization of the mixed olfactory/trigeminal stimulus but inability to localize the pure olfactory stimulus. Our results suggest that localization of chemosensory stimuli relies, at least in part, on CC, highlighting its role in interhemispheric communication for olfactory processing. The varying odor localization performance observed in participants with agenesis of CC indicates that compensatory mechanisms may be promoted in some cases, potentially preserving normal localization functions despite the absence of major commissural pathways.

Taste buds are commonly studied in rodent models, but some differences exist between mice and humans in terms of gustatory mechanisms and sensitivities. Whether these functional differences are reflected in structural differences between species is unclear. Using immunofluorescent image stacks, we compared the morphological and molecular characteristics of mouse and human fungiform taste buds. The results suggest that while the general features of fungiform taste buds are similar between mice and humans, several characteristics differ significantly. Human taste buds are larger and taller than those of mice, yet they contain similar numbers of taste cells. Taste buds in humans are more heavily innervated by gustatory nerve fibers expressing the purinergic receptor P2X3 showing a 40% higher innervation density than in mice. Like type II cells of mice, a subset (about 30%) of cells in human taste buds is immunoreactive for phospholipase C beta (PLCβ2). These PLCβ2-immunoreactive cells display calcium homeostasis modulator 1 (CALHM1)-immunoreactive puncta closely opposed to gustatory nerve fibers suggestive of channel-type synapses in type II cells in mice. These puncta, used as a measure of synaptic contact, are significantly larger in humans compared to mice suggesting a higher efflux of adenosine triphosphate (ATP) neurotransmitter in humans. Altogether these findings suggest that while many similarities exist in the organization of murine and human fungiform taste buds, significant differences do exist in taste bud size, innervation density, and size of synaptic contacts that may impact gustatory signal transmission.

Naming common odors can be an exceptionally challenging task even for young and healthy individuals. Due to this difficulty, tests of cued odor identification (OID) are used instead of free odor identification in cognitive, neuropsychological, or aging research. Consequently, our understanding of the cognitive demands of free OID is limited. In this study, we analyze the demographic and cognitive factors that influence OID responses of old adults. We utilize a uniquely large dataset (n = 2,479) from a population-based sample of healthy, older Swedish adults (ages 58-102) who participated in free and cued OID using the 16-item Sniffin' TOM test. The free OID naming responses were categorized as correct, misnamings, or omissions. The results revealed that omissions are surprisingly prevalent, constituting 66.4% of errors and accounting for 87.7% of the age-related differences in task performance. Additionally, we hypothesized that successful free OID would be more closely linked to nonolfactory cognitive abilities, such as verbal fluency, vocabulary, and episodic memory proficiency. This hypothesis was supported, as we found significant associations between free OID and these cognitive abilities, while cued OID identification only was associated with perceptual speed. Our findings suggest that the assessment of free OID may provide valuable insights into odor-based cognition, indicating a need for further research in this area.

Humans possess a remarkable ability to discriminate a wide range of odors with high precision. This process begins with olfactory receptors (ORs) detecting and responding to the molecular structures of odorants. Recent studies have aimed to associate the activity of a single OR to an odor descriptor or predict odor descriptors using 2D molecular representation. However, predicting a limited number of odor descriptors is insufficient to fully understand the widespread and elaborate olfactory perception process. Therefore, we conducted structure-activity relationship analyses for ORs of eugenol, vanillin, and structurally similar compounds, investigating the correlation between molecular structures, OR activity profiles, and perceptual odor similarity. Our results indicated that these structurally similar compounds primarily activated 6 ORs, and the activity profiles of these ORs correlated with their perception. This enabled the development of a prediction model for the eugenol-similarity score from OR activity profiles (coefficient of determination, R2 = 0.687). Furthermore, the molecular structures of odorants were represented as 3D shapes and pharmacophore fingerprints, considering the 3D structural similarities between various odorants with multiple conformations. These 3D shape and pharmacophore fingerprints could also predict the perceptual odor similarity (R2 = 0.514). Finally, we identified key molecular structural features that contributed to predicting sensory similarities between compounds structurally similar to eugenol and vanillin. Our models, which predict odor from OR activity profiles and similarities in the 3D structure of odorants, may aid in understanding olfactory perception by compressing the information from a vast number of odorants into the activity profiles of 400 ORs.

Mechanisms of olfactory training (OT) in older adults require a more thorough investigation, considering its potential beneficial effects in age-related olfactory, cognitive, and affective decline. To address this question, we examined the role of OT odor hedonics in 128 participants aged between 50 and 85 yr (Mage = 68.2 ± 7.4; 105 women and 23 men). Additionally, we explored the role of physical activity in olfactory function, depression scores, and verbal fluency. Participants were randomly assigned to 1 of 4 groups, of which 2 performed OT with either (i) pleasant or (ii) unpleasant odors, or (iii) performed physical exercises and no OT or (iv) a control group without OT or physical exercises. Results indicate a beneficial effect of OT, both with pleasant and unpleasant odors, on one key domain of cognitive function, namely verbal fluency. Furthermore, physical exercise alone also caused an increase in verbal fluency. Finally, a significant beneficial effect of OT on depression score was noted, but only in the group that displayed relatively robust depression symptoms in the pre-training session. OT may be of particular use for older people due to their risk of age-related cognitive decline and depression.

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.

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.