Chemical Senses最新文献

Many animals transmit information in the form of chemical signals to modify behavior or induce physiological change in receivers. For some taxa, such as species in the order Carnivora, chemical signals are known to provide a critical mode of communication, although they are still poorly understood compared to other signal modalities. Here, we review the literature to identify and categorize potential chemical signals within the Carnivora with a view to determining commonalities based on sex, taxon, and function. Data were drawn from 112 publications, dating from 1896 to 2021. Of the 1,532 discrete chemicals identified, 169 were detected in > 5 species, with 58 found in ≥ 10 species. However, multiple different names were often used to report the same compound, reducing the transparency of the literature. Two hundred and fifty-two chemicals were identified as biomarkers, i.e. associated with specific behavioral contexts (dominance hierarchy, appeasement, agonistic, etc.) or specific demographic traits (age, sex, etc.). Few studies established a causal link between these biomarkers and behavioral or physiological changes, so only a few could be definitively described as behaviorally functional bioactive signals. We found high variability concerning which species, chemicals, and sources were represented in the literature, which could potentially lead to a perceptual bias in the relative importance of certain chemicals. Finally, we propose a method for standardized reporting of chemical signals and suggest that future work should focus on a more consistent expansion of the range of species, products, and chemical types analyzed so that the phylogenetic relationship of chemical signals across taxa can be determined.

In the nasal cavity, olfactory receptor neurons are situated in the sensory epithelium and act to transduce odor signals, whereas the respiratory epithelium is responsible for removing unwanted particles from inhaled air. Although several molecular markers have been identified to define multiple specific cell types in the sensory epithelium, less is known to indicate cells in the respiratory domain. We have recently shown that the non-visual photoreceptor opsin 3 (Opn3) is expressed in the developing olfactory region. This raised the question as to which functional role/s Opn3 might play in the nasal epithelium, as well as whether other non-visual photoreceptors may be expressed in this region. By using Opn3-eGFP and Opn5-tdTomato reporter mice in combination with Foxj1, Ker8, OMP, Sox2, and Tubb3 immunohistochemistry analyzes, our findings show that Opn3 is restricted to the olfactory sensory domain from early embryonic stages, whereas Opn5 is up-regulated in the respiratory epithelium at later developmental stages. In adulthood, Opn3 is expressed in Sox2/Ker8-positive sustentacular cells in the sensory epithelium, whereas Opn5 expression remains in the respiratory epithelium, thus indicating that these molecular markers could be used to distinguish the sensory versus respiratory epithelia. Studies of morphology and expression patterns of Foxj1, Ker8, OMP, Sox2, and Tubb3 in adult Opn3-/- and Opn5-/- mice did not reveal differences from wild-type mice. In addition, neither Opn3-/- nor Opn5-/- mice exhibited a disturbance in olfaction compared to wild-type littermates when performing a buried food test.

Many species of animals rely on their chemical senses to detect tastants and odorants to guide dietary selection, avoid danger, and modulate social interactions, all of which ultimately enhance survival and fitness. Significant progress has been made in our understanding of the 2 major chemosensory systems, taste and smell, through studies in model organisms such as flies and mice, ranging from receptor identification to sensory coding mechanisms. These topics have been extensively reviewed elsewhere. Here, we will instead focus on less commonly used model systems and companion animals, examining how taste receptors have been shaped by feeding ecology over the course of evolution to illustrate the concept that each species lives in its own sensory world, finely tuned to its ecological niche.

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.

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.

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.

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.

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.