Chemical Senses最新文献

Attempts to map odor percepts to physical and chemical parameters have a long and challenging history. In contrast to color vision, where three classes of photoreceptors respond to the same stimulus property (wavelength), ~400 classes of olfactory receptors are available to respond in a non-linear non-additive fashion to ~5000 different chemical parameters. Theoretically, millions of permutations between structural elements of chemicals and their smells are possible, and some chemicals with different structures have the same odor and vice versa. Importantly, the same odor quality can come from multiple environmental objects and most odors depend upon the synthesis of a complex melody of volatile chemicals that individually can have dissimilar smells. At the individual receptor level, both agonists and antagonists within a mixture can impact receptor function. Hence, it is perhaps not surprising that no universal relationship between odor quality and underlying physical or chemical dimensions analogous to spectral wavelength for vision or air pressure waves for hearing has yet been identified. This review provides a historical account of psychological odor categorization, attempts to map odor percepts to physiochemical parameters, and attendant pitfalls. It concludes that perceived odor qualities may be best viewed as cognitive constructs with attendant variability due to individual experiences, linguistic processes, and biologic factors that do not map well to universal physiochemical dimensions.

Amino acids (AAs) are essential dietary macronutrients that impact an organism's fitness in a concentration-dependent manner, but the mechanisms mediating AA detection to drive consumption are less clear. In Drosophila, we identified the repertoire of taste cells and receptors that are salient for feeding initiation when flies encounter a glutamate-rich AA peptide mixture, tryptone, using in vivo calcium imaging and the proboscis extension response. We found that tryptone attraction occurs through sweet cells, whereas feeding aversion is mediated through Ionotropic Receptor 94e (IR94e) cells and bitter cells, dependent on concentration. Further, our results corroborate previous findings that IR76b, IR51b, and IR94e detect AAs in specific cell types, even when exposed to a more complex peptide mixture. Additionally, we describe a new role for the appetitive IR56d receptor and bitter gustatory receptors in sensing tryptone. This work establishes a cellular and molecular framework salient for AA and peptide feeding initiation and highlights redundancy in aversive pathways that regulate AA feeding.

Odors convey useful navigational and episodic information, yet much of the chemical world remains inaccessible without active sampling through sniffing. Respiratory cycles control odor dynamics within the nose, so understanding olfactory bulb (OB) neural dynamics requires accurate respiratory measurements. While respiratory behavior can be measured directly with a variety of chronic methods, these methods are invasive, and none are perfectly robust. OB local field potentials (LFPs) have long been known to couple with respiration. Here, we investigated whether the precise timing and frequency of respiration can be inferred from OB LFPs. Our results replicate previous findings that OB LFPs across multiple frequency bands align with respiratory cycles. Further, these OB rhythms are locked to time in the respiratory cycle, and not phase. In addition, we show that 2 to 12 Hz LFP oscillations effectively track sniffing rate. However, a monotonic relationship between LFP-respiratory delay and sniffing rate, which varies across animals, renders the recovery of precise respiratory events challenging. This work underscores the complex and individualized relationship between rodent respiration and OB LFPs, contributing to our understanding of how respiration controls olfaction.

We perceive our environment via different sensory channels in a multisensory fashion. During multisensory integration, these channels can enhance or hinder each other depending on congruency. Here, we aimed to investigate how the congruency of gustatory and visual costimulation alter the perception of olfactory stimuli. We hypothesized that congruent costimulation enhances the perception of likeness, i.e. how well stimuli match a label, compared with no and to incongruent costimulation. We also aimed to quantify the effect of gustatory and visual costimulation. We tested 48 healthy young participants. We used retronasal olfactory stimuli (strawberry, cheese, lemon, and coffee) (i) alone or with congruent/incongruent costimulation ((ii) with congruent gustatory (sweet, salty, sour, and bitter), (iii) with congruent visual (images of strawberry, cheese, lemon, and coffee), (iv) with congruent visual and gustatory, (v) with congruent visual and incongruent gustatory, (vi) with congruent gustatory and incongruent visual, (vii) with incongruent visual and gustatory costimulations). Olfactory and gustatory stimuli were presented by means of droplets on the tongue, i.e. olfactory stimuli were delivered retronasally, while visual stimuli were presented on a computer screen. We asked participants to evaluate the solutions' likeness to the respective olfactory label on visual analog scales. We observed a significant effect of congruency on likeness (P < 0.001). Gustatory costimulation had a significantly stronger effect than visual costimulation (P = 0.02). Congruent costimulation enhances the evaluation of likeness while incongruent costimulation reduces it, with gustatory costimulation having significantly stronger effects than visual costimulation. This could be useful in multisensory olfactory training paradigms for olfactory loss.

The sense of smell is generated by electrical currents that are influenced by the concentration of ions in olfactory sensory neurons and mucus. In contrast to the extensive morphological and molecular characterization of sensory neurons, there has been little description of the cells that control ion concentrations in the zebrafish olfactory system. Here, we report the molecular and ultrastructural characterization of zebrafish olfactory ionocytes. Transcriptome analysis suggests that the zebrafish olfactory epithelium contains at least three different ionocyte types, which resemble Na+/K+-ATPase-rich (NaR), H+-ATPase-rich (HR), and Na+/Cl- cotransporter (NCC) cells, responsible for calcium, pH, and chloride regulation, respectively, in the zebrafish skin. In the olfactory epithelium, NaR-like and HR-like ionocytes are usually adjacent to one another, whereas NCC-like cells are usually solitary. The distinct subtypes are differentially distributed: NaR-like/HR-like cell pairs are found broadly within the olfactory epithelium, whereas NCC-like cells reside within the peripheral non-sensory multiciliated cell zone. Comparison of gene expression and serial-section electron microscopy analysis indicates that the NaR-like cells wrap around the HR-like cells and are connected to them by shallow tight junctions. The development of olfactory ionocyte subtypes is also differentially regulated, as pharmacological Notch inhibition leads to a loss of NaR-like and HR-like cells, but does not affect NCC-like ionocyte number. These results provide a molecular and anatomical characterization of olfactory ionocytes in a stenohaline freshwater teleost. The paired ionocytes suggest that both transcellular and paracellular transport regulate ion concentrations in the olfactory epithelium, while the solitary ionocytes may enable independent regulation of ciliary beating.

Working memory (WM) processes are assumed to operate on a wide variety of sensory materials, yet WM research rarely extends beyond sight and hearing. In this systematic review, we integrate research from studies that address WM in olfaction, the sense of smell, spanning the last 50 yr (N = 44). We assessed whether 21 proposed "benchmarks" for WM generalize to olfactory WM. Seven benchmarks generalized to olfaction, whereas 2 failed to generalize. Evidence was insufficient to address the remaining 12 benchmarks (4 had mixed support and 8 were yet unaddressed). We conclude that the available evidence indicates that the sense of smell has a short-term memory system that mostly resembles WM processes in "higher" senses, although there are exceptions related to how olfactory WM performance is associated with other functions. We argue that researchers studying WM should explicitly consider evidence outside of the audio-visual senses when establishing theoretical frameworks. Further, we point out avenues for future research that may help close the remaining gaps in knowledge on this neglected topic.

Dogs, domesticated from gray wolves over 15,000 yr ago, exhibit extensive variation among breeds, including differences in olfactory ability. To investigate the genetic basis of these differences, we analyzed single-nucleotide variants (SNVs) in 3 chemosensory receptor gene families-olfactory receptors (ORs), vomeronasal receptors type 1 (V1Rs), and bitter taste receptors (T2Rs)-using whole-genome data from the Dog Biomedical Variant Database Consortium, which includes 635 domestic dogs representing 121 breeds and 8 wolves. We identified 179 segregating pseudogenes in OR genes (minor allele frequency > 1%), including cases where intact genes are pseudogenized in some individuals and vice versa. The number of functional OR genes varied substantially among individuals (779 to 807), while V1R and T2R gene counts were nearly invariant (8 and 16, respectively). Compared to wolves, dogs exhibited significantly higher ratios of nonsynonymous to synonymous SNVs (N/S) in OR and T2R genes, suggesting relaxed functional constraints potentially associated with domestication. Among breeds, Pugs had significantly fewer functional OR genes and a higher N/S ratio than other breeds, even after accounting for copy number variation. Notably, an OR gene orthologous to the human androstenone receptor, OR7D4, was completely pseudogenized in all Pugs but remained largely functional in other breeds. These findings support the hypothesis that reduced olfactory ability in brachycephalic breeds, such as Pugs, is associated with genetic degeneration of OR genes. Overall, our study provides new insights into the genetic diversity of chemosensory receptor repertoires in dogs and underscores the impact of domestication and breed-specific morphological traits on olfactory function.

Recent research has shown that KATP channels in mouse taste bud cells enhance glucose taste signaling by depolarizing the cell when ATP is present. Relatedly, estradiol has been shown to enhance glucose sensing in human pancreatic β cells via closure of KATP channels. Since taste tissue has estradiol receptors, we linked these 2 observations and tested whether elevated estradiol may also enhance taste sensitivity and liking for glucose in humans. We hypothesized that around the time of ovulation, when estrogen peaks during the menstrual cycle in female participants, oral taste detection thresholds for glucose (metabolizable monosaccharide) would decrease but would not for sucralose or the glucose analog methyl-D-glucopyranoside (MDG) (both nonmetabolizable sweeteners that do not close KATP channels). Fifteen healthy eumenorrheic females were asked to track their urinary estrogen metabolite estrone-3-glucuronide (E3G) via a fertility monitor. The participants were tested using oral detection thresholds for glucose, sucralose and MDG during the E3G nadir at menstruation and E3G peak (>100 ng/mL) at peri-ovulation. Seven male participants were also tested for glucose detection thresholds over the same 2-wk interval. Female participants were also asked to rate their liking for glucose solutions at mildly sweet (450 mM) and moderately sweet (900 mM) concentrations. Detection thresholds for glucose, but not sucralose or MDG, decreased peri-ovulation during estrogen peak (P < 0.05), indicating enhanced sensitivity to glucose specifically. Males showed no change in glucose threshold over the 2 wk. Liking ratings for 900 mM glucose tended to increase during ovulation (P = 0.06). These observations are consistent with the idea that estrogen and/or other co-modulating hormones, such as luteinizing hormone and progesterone, enhance a metabolic signaling pathway during the peri-ovulatory phase.

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.

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.