Taste cells expressing Ionotropic Receptor 94e reciprocally impact feeding and egg laying in Drosophila.

Chemosensory cells across the body of Drosophila melanogaster evaluate the environment to prioritize certain behaviors. Previous mapping of gustatory receptor neurons (GRNs) on the fly labellum identified a set of neurons in L-type sensilla that express Ionotropic Receptor 94e (IR94e), but the impact of IR94e GRNs on behavior remains unclear. We used optogenetics and chemogenetics to activate IR94e neurons and found that they drive mild feeding suppression but enhance egg laying. In vivo calcium imaging revealed that IR94e GRNs respond strongly to certain amino acids, including glutamate, and that IR94e plus co-receptors IR25a and IR76b are required for amino acid detection. Furthermore, IR94e mutants show behavioral changes to solutions containing amino acids, including increased consumption and decreased egg laying. Overall, our results suggest that IR94e GRNs on the fly labellum discourage feeding and encourage egg laying as part of an important behavioral switch in response to certain chemical cues.

The distribution and chemosensory responses of pharyngeal taste buds in the sea lamprey Petromyzon marinus.

Little is known about the chemosensory system of gustation in sea lampreys, basal jawless vertebrates that feed voraciously on live prey. The objective of this study was to investigate taste bud distribution and chemosensory responses along the length of the pharynx in the sea lamprey. Scanning electron microscopy and immunocytochemistry revealed taste buds and associated axons at all six lateral pharyngeal locations between the seven pairs of internal gill pores. The most rostral pharyngeal region contained more and larger taste buds than the most caudal region. Taste receptor cell responses were recorded to sweet, bitter, amino acids and the bile acid taurocholic acid, as well as to adenosine triphosphate. Similar chemosensory responses were observed at all six pharyngeal locations with taste buds. Overall, this study shows prominent taste buds and taste receptor cell activity in the seven pharyngeal regions of the sea lamprey.

Subjective versus Psychophysical Measures of Chemosensory Alterations following COVID-19.

INTRODUCTION: Olfactory dysfunction is a common symptom of COVID-19. However, subjective perception of olfactory function does not always correlate well with more objective measures. This study seeks to clarify associations between subjective and psychophysical measures of olfaction and gustation in patients with subjective chemosensory dysfunction following COVID-19. METHODS: Adults with persistent COVID-19-associated chemosensory disturbance were recruited for a prospective, longitudinal cohort study at a tertiary care institution. Participants provided subjective measures of olfactory and gustatory function and underwent psychophysical assessment using Sniffin' Sticks olfactory and Monell gustatory tests. RESULTS: Data analysis (n = 65) showed a statistically significant association between subjective and psychophysical measures of olfaction (p < 0.001). For each one-point increase in subjectively-reported olfactory ability, there is, on average, a 0.11 (95% CI: 0.06, 0.16; p < 0.001) point increase in TDI score while adjusting for age at baseline assessment, sex, and follow-up time. For each one-point increase in subjectively-reported olfactory ability, there is, on average, a 0.04 (95% CI: 0.02, 0.06; p < 0.001) point and 0.05 (95% CI: 0.03, 0.07; p < 0.001) point increase in discrimination and identification scores, respectively, when adjusting for age at baseline assessment, sex, and follow-up time. CONCLUSION: Subjective olfaction shows a mild to moderate association with psychophysical measures, but it fails to comprehensively assess persistent COVID-19-associated chemosensory deficits. The lack of significant association between subjective olfaction and threshold limits the utility of subjective olfaction in tracking recovery. These findings support the push for more widespread psychophysical chemosensory testing.

Impact of obstructive sleep apnea syndrome on olfactory and gustatory capacity.

Only a few studies have investigated olfactory function in patients with obstructive sleep apnea syndrome (OSAS) using psychophysical testing, and there is a scarcity of data regarding taste evaluation in the existing literature. The primary objectives of this study were to assess both smell and taste in patients with OSAS and to explore the correlation between the severity of symptoms and sensory perception. A total of 85 OSAS patients and a control group comprising 81 subjects were enrolled. Initial assessments included anamnesis, nasal endoscopy, and the completion of questionnaires (Epworth Sleepiness Scale, Visual Analogue Scale, Questionnaire of Olfactory Disorders, and the importance of olfaction questionnaire). The diagnosis of OSAS was confirmed by polysomnography, while nasal airflow was evaluated using rhinomanometry. Olfaction was assessed using the Sniffin' Sticks test, and the Threshold-Discrimination-Identification (TDI) score was calculated. Taste evaluation was conducted in a subgroup of participants (42 patients, 38 controls) using taste strips. The mean TDI score was 31 ±â€…5.6 for OSAS patients and 35 ±â€…4.6 for controls, indicating a significant difference (P < 0.001). Similarly, the taste score was 7 ±â€…3.0 for OSAS patients and 12.6 ±â€…3.2 for controls (P < 0.001). No correlations were observed between TDI and Apnea Hypopnea Index (AHI) (r = -0.12; P = 0.28), as well as between the taste score and AHI (r = -0.31; P = 0.22). However, a weak but significant correlation between TDI score and Epworth Sleepiness Scale was detected (r = -0.05; P = 0.002). The study revealed a significant decrease in sensory perception among patients with OSAS, though open questions persist about the pathophysiology.

Tastant-receptor interactions: insights from the fruit fly.

Across species, taste provides important chemical information about potential food sources and the surrounding environment. As details about the chemicals and receptors responsible for gustation are discovered, a complex view of the taste system is emerging with significant contributions from research using the fruit fly, Drosophila melanogaster, as a model organism. In this brief review, we summarize recent advances in Drosophila gustation and their relevance to taste research more broadly. Our goal is to highlight the molecular mechanisms underlying the first step of gustatory circuits: ligand-receptor interactions in primary taste cells. After an introduction to the Drosophila taste system and how it encodes the canonical taste modalities sweet, bitter, and salty, we describe recent insights into the complex nature of carboxylic acid and amino acid detection in the context of sour and umami taste, respectively. Our analysis extends to non-canonical taste modalities including metals, fatty acids, and bacterial components, and highlights unexpected receptors and signaling pathways that have recently been identified in Drosophila taste cells. Comparing the intricate molecular and cellular underpinnings of how ligands are detected in vivo in fruit flies reveals both specific and promiscuous receptor selectivity for taste encoding. Throughout this review, we compare and contextualize these Drosophila findings with mammalian research to not only emphasize the conservation of these chemosensory systems, but to demonstrate the power of this model organism in elucidating the neurobiology of taste and feeding.

Disruption of Zfh3 abolishes mulberry-specific monophagy in silkworm larvae.

Feeding behavior is critical for insect survival and fitness. Most researchers have explored the molecular basis of feeding behaviors by identifying and elucidating the function of olfactory receptors (ORs) and gustatory receptors (GRs). Other types of genes, such as transcription factors, have rarely been investigated, and little is known about their potential roles. The silkworm (Bombyx mori) is a well-studied monophagic insect which primarily feeds on mulberry leaves, but the genetic basis of its monophagy is still not understood. In this report, we focused on a transcription factor encoded by the Zfh3 gene, which is highly expressed in the silkworm central and peripheral nervous systems, including brain, antenna, and maxilla. To investigate its function, Zfh3 was abrogated using clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR associated protein 9 (Cas9) mutagenesis. Since Zfh3 knockout homozygotes are not viable, we studied feeding behavior in heterozygotes, and found that disruption of Zfh3 affects both gustation and olfaction. Mutant larvae lose preference for mulberry leaves, acquire the ability to consume an expanded range of diets, and exhibit improved adaptation to the M0 artificial diet, which contains no mulberry leaves. These results provide the first demonstration that a transcription factor modulates feeding behaviors in an insect.

Change in taste sensation after orthognathic surgery.

OBJECTIVE: The objective of this study was to evaluate the effect of orthognathic surgery on taste sensation. MATERIALS AND METHODS: Thirty-five patients scheduled to undergo Le Fort I osteotomy (LFIO), sagittal split ramus osteotomy (SSRO), and bimaxillary surgery (BMS) were evaluated by administering localized and whole-mouth taste tests preoperatively and postoperatively at months 1, 3, and 6. The patients were asked to identify the quality of four basic tastes applied to six locations on the palate and tongue and to rate the taste intensities they perceived. Taste recognition thresholds and taste intesity scores were evaluted according to operation groups and follow-ups. RESULTS: There were significant decreases in the quinine HCl recognition thresholds at the postoperative follow-ups compared to the preoperative in LFIO patients (p = 0.043). There were significant decreases in sucrose taste intensity scores in the right posterolateral part of the tongue at months 3 and 6 compared to preoperative in SSRO patients (p = 0.046), and significant increases in quinine HCL taste intensity scores in the right and left anterior parts of the tongue at month 6 compared to preoperative in LFIO patients (p < 0.05). CONCLUSION: Taste perception is affected due to potential damage to the chemosensory nerves during orthognathic surgical procedures. Generally, non-significant alterations have been observed in taste perception after orthognathic surgery, except for significant alterations in bitter and sweet taste perceptions. CLINICAL RELEVANCE: Maxillofacial surgeons should be aware of taste perception change after orthognathic surgery procedures and patients should be informed accordingly. THE TRIAL REGISTRATION NUMBER (TRN): NCT06103422/Date of registration: 10.17.2023 (retrospectively registered).

Structural basis of ligand specificity and channel activation in an insect gustatory receptor.

Gustatory receptors (GRs) are critical for insect chemosensation and are potential targets for controlling pests and disease vectors, making their structural investigation a vital step toward such applications. We present structures of Bombyx mori Gr9 (BmGr9), a fructose-gated cation channel, in agonist-free and fructose-bound states. BmGr9 forms a tetramer similar to distantly related insect odorant receptors (ORs). Upon fructose binding, BmGr9's channel gate opens through helix S7b movements. In contrast to ORs, BmGr9's ligand-binding pocket, shaped by a kinked helix S4 and a shorter extracellular S3-S4 loop, is larger and solvent accessible in both agonist-free and fructose-bound states. Also, unlike ORs, fructose binding by BmGr9 involves helix S5 and a pocket lined with aromatic and polar residues. Structure-based sequence alignments reveal distinct patterns of ligand-binding pocket residue conservation in GR subfamilies associated with different ligand classes. These data provide insight into the molecular basis of GR ligand specificity and function.

Identification and functional characterization of chemosensory genes in olfactory and taste organs of Spodoptera litura (Lepidoptera: Noctuidae).

The tobacco cutworm Spodoptera litura is one of the most destructive polyphagous crop pests. Olfaction and taste play a crucial role in its host plant selection and sexual communication, but the expression profile of chemosensory genes remains unclear. In this study, we identified 185 chemosensory genes from 7 organs in S. litura by transcriptome sequencing, of which 72 genes were published for the first time, including 27 odorant receptors (ORs), 26 gustatory receptors (GRs), 1 ionotropic receptor (IR), 16 odorant-binding proteins (OBPs), and 2 chemosensory proteins (CSPs). Phylogenetic analyses revealed that ORs, IRs, OBPs, and sensory neuron membrane proteins (SNMPs) were mainly expressed in antennae and sequence-conserved among Noctuidae species. The most differentially expressed genes (DEGs) between sexes were ORs and OBPs, and no DEGs were found in GRs. GR transcripts were enriched in proboscis, and the expression of sugar receptors was the highest. Carbon dioxide receptors, sugar receptor-SliuGR6, and bitter GRs-SlituGR43 and SlituGR66 had higher sequence identities between Noctuidae species. CSPs were broadly expressed in various organs, and SlituCSP13 was a DEG in adult antennae. The functional analysis in the Drosophila OR67d expression system found that SlituOR50, a receptor highly expressed in female antennae, is selectively tuned to farnesyl acetate. The results provide a solid foundation for understanding the molecular mechanisms by which chemosensory genes operate to elicit behavioral responses in polyphagous insects.

Taste and smell function in Wilson's disease.

OBJECTIVE: Wilson's disease (WD) is a metabolic disorder associated with abnormal copper metabolism that results in hepatic, psychiatric, and neurologic symptoms. No investigation of taste function has been made in patients with WD, although olfactory dysfunction has been evaluated. METHODS: Quantitative taste and smell test scores of 29 WD patients were compared to those of 790 healthy controls. Taste was measured using the 53-item Waterless Empirical Taste Test (WETT®) and smell using the 40-item revised University of Pennsylvania Smell Identification Test (R-UPSIT®). Multiple linear regression analysis controlled for age and sex. RESULTS: Average WETT® scores did not differ meaningfully between WD and control subjects (respective medians & IQRs = 32 [28-42] & 34 [27-41]); linear regression coefficient = 1.19, 95% CI [-0.81, 3.19], p = 0.242). In contrast, WD was associated with significantly reduced olfactory function [respective median (IQR) R-UPSIT® scores = 35 (33-37) vs. 37 (35-38); adjusted linear regression coefficient = -1.59, 95% CI [-2.34, -0.833]; p < 0.001)]. Neither olfaction nor taste were influenced by WD symptom subtype [23 (79.3%) were hepatic-predominant; 6 (20.7%) neurologic predominant]; R-UPSIT®, p = 0.774; WETT®, p = 0.912). No effects of primary medication or years since diagnosis (R-UPSIT®, p = 0.147; WETT®, p = 0.935) were found. Weak correlations were present between R-UPSIT® and WETT® scores for both control (r=0.187, p < 0.0001) and WD (r=0.237) subjects, although the latter correlation did not reach the 0.05 α level (p = 0.084). CONCLUSION: Although WD negatively impacts smell function, taste is spared. Research is needed to understand the pathophysiologic mechanisms responsible for this divergence.

What are olfaction and gustation, and do all animals have them?

Different animals have distinctive anatomical and physiological properties to their chemical senses that enhance detection and discrimination of relevant chemical cues. Humans and other vertebrates are recognized as having 2 main chemical senses, olfaction and gustation, distinguished from each other by their evolutionarily conserved neuroanatomical organization. This distinction between olfaction and gustation in vertebrates is not based on the medium in which they live because the most ancestral and numerous vertebrates, the fishes, live in an aquatic habitat and thus both olfaction and gustation occur in water and both can be of high sensitivity. The terms olfaction and gustation have also often been applied to the invertebrates, though not based on homology. Consequently, any similarities between olfaction and gustation in the vertebrates and invertebrates have resulted from convergent adaptations or shared constraints during evolution. The untidiness of assigning olfaction and gustation to invertebrates has led some to recommend abandoning the use of these terms and instead unifying them and others into a single category-chemical sense. In our essay, we compare the nature of the chemical senses of diverse animal types and consider their designation as olfaction, oral gustation, extra-oral gustation, or simply chemoreception. Properties that we have found useful in categorizing chemical senses of vertebrates and invertebrates include the nature of peripheral sensory cells, organization of the neuropil in the processing centers, molecular receptor specificity, and function.

Behavioral Tests for Associative Learning in Caenorhabditis elegans.

Learning is critical for survival as it provides the capacity to adapt to a changing environment. At the molecular and cellular level, learning leads to alterations within neural circuits that include synaptic rewiring, synaptic plasticity, and protein level/gene expression changes. There has been substantial progress in recent years on dissecting how learning and memory is regulated at the molecular and cellular level, including the use of compact invertebrate nervous systems as experimental models. This progress has been facilitated by the establishment of robust behavioral assays that generate a quantifiable readout of the extent to which animals learn and remember. This chapter will focus on protocols of behavioral tests for associative learning using the nematode Caenorhabditis elegans, with its unparalleled genetic tractability, compact nervous system of ~300 neurons, high level of conservation with mammalian systems, and amenability to a suite of behavioral tools and analyses. Specifically, we will provide a detailed description of the methods for two behavioral assays that model associative learning, one measuring appetitive olfactory learning and the other assaying aversive gustatory learning.

Gustatory and olfactory shifts during pregnancy and the postpartum period: A systematic review and meta-analysis.

Pregnancy is a transformative phase marked by significant behavioral and physiological changes. Substantial changes in pregnancy-related hormones are thought to induce changes in chemosensory perception, as often observed in non-human animals. However, empirical behavioral research on pregnancy-related olfactory or gustatory changes has not yet reached a consensus. This PROSPERO pre-registered systematic review and meta-analysis evaluated published data of olfactory and gustatory changes in pregnant individuals, across the three pregnancy trimesters and postpartum period. Our comprehensive search strategy identified 20 relevant studies, for inclusion in the meta-analysis. The meta-analysis revealed that pregnant individuals, regardless of trimester, performed significantly poorer in terms of odour identification, however, no difference was detected between non-pregnant controls and women postpartum. Additionally, pregnant women in the second and third trimester rated olfactory stimuli to be more intense. A slight decline in odour pleasantness ratings was observed amongst those in the second trimester. No major difference was observed between pregnant and non-pregnant subjects in terms of gustatory functions, except the first trimester appeared to be associated with increased pleasantness for the sweet taste. Post-hoc meta-regression analyses revealed that pregnancy stage was a significant predictor for observed effect size for odour intensity ratings, but not for odour identification scores. These findings provide valuable insights into the interplay between pregnancy and chemosensory perception, highlighting systematic physiological changes due to pregnancy. Healthcare providers can also utilize the knowledge of sensory shifts to better support pregnant women in making appropriate dietary choices, managing sense-related discomfort, and leading to potential sensory interventions. Overall, this research enhances our comprehension of sensory shifts during pregnancy, benefiting maternal health and pregnancy-related care.

Mouthparts of the bumblebee (Bombus terrestris) exhibit poor acuity for the detection of pesticides in nectar.

Bees are important pollinators of agricultural crops, but their populations are at risk when pesticides are used. One of the largest risks bees face is poisoning of floral nectar and pollen by insecticides. Studies of bee detection of neonicotinoids have reported contradictory evidence about whether bees can taste these pesticides in sucrose solutions and hence avoid them. Here, we use an assay for the detection of food aversion combined with single-sensillum electrophysiology to test whether the mouthparts of the buff-tailed bumblebee (Bombus terrestris) detect the presence of pesticides in a solution that mimicked the nectar of oilseed rape (Brassica napus). Bees did not avoid consuming solutions containing concentrations of imidacloprid, thiamethoxam, clothianidin, or sulfoxaflor spanning six orders of magnitude, even when these solutions contained lethal doses. Only extremely high concentrations of the pesticides altered spiking in gustatory neurons through a slight reduction in firing rate or change in the rate of adaptation. These data provide strong evidence that bumblebees cannot detect or avoid field-relevant concentrations of pesticides using information from their mouthparts. As bees rarely contact floral nectar with other body parts, we predict that they are at high risk of unwittingly consuming pesticides in the nectar of pesticide-treated crops.

Bees and other pollinators often encounter pesticides while collecting nectar and pollen from agricultural crops. Widely used to protect crops, pesticides are toxic to insects and have contributed to population declines in all bee species. One way that bees might be able to avoid pesticides is using their incredibly good sense of taste, which can detect subtle differences between sugary solutions. Therefore, if pesticides taste bitter to them, bumblebees may be able to avoid feeding treated crops. However, it was not clear if bees can taste pesticides. Previous studies investigating whether they can taste a group of pesticides called "neonicotinoids" gave contradictory results. Furthermore, explicit behavioural tests of their ability to taste pesticides had not been performed. To shed light on this, Parkinson et al. compared the responses of neurons within structures used for detecting taste in bumblees eating a pure sugar solution with those eating a solution containing pesticides. Experiments with a group of pesticides known as 'cholinergic' showed that neuron responses were the same whether the sugar solution contained pesticides or not. Secondly, by looking at bumblebee feeding behaviour, Parkinson et al. found that bees offered both pure and pesticide-laced sugar solutions would still drink the pesticide solution, even when it was toxic enough to make them very ill or kill them. This was the case regardless of which pesticide was used. The experiments showed that bumblebees cannot use their sense of taste to avoid drinking pesticide-laced nectar, which is an important finding for policymakers making decisions about the use of pesticides on agricultural crops. It is possible that bees simply have a poor sense of bitter taste. However, in the future, these methods could be used to identify a compound that tastes bad to bees. Including such a compound in pesticides, could deter bees from feeding on pesticide-treated crops that do not require pollination, and help to restore their declining populations.

Structure of an insect gustatory receptor.

Gustatory Receptors (GRs) are critical for insect chemosensation and are potential targets for controlling pests and disease vectors. However, GR structures have not been experimentally determined. We present structures of Bombyx mori Gr9 (BmGr9), a fructose-gated cation channel, in agonist-free and fructose-bound states. BmGr9 forms a tetramer similar to distantly related insect Olfactory Receptors (ORs). Upon fructose binding, BmGr9's ion channel gate opens through helix S7b movements. In contrast to ORs, BmGR9's ligand-binding pocket, shaped by a kinked helix S4 and a shorter extracellular S3-S4 loop, is larger and solvent accessible in both agonist-free and fructose-bound states. Also unlike ORs, fructose binding by BmGr9 involves helix S5 and a binding pocket lined with aromatic and polar residues. Structure-based sequence alignments reveal distinct patterns of ligand-binding pocket residue conservation in GR subfamilies associated with distinct ligand classes. These data provide insight into the molecular basis of GR ligand specificity and function.

Neuroanatomy of the Cetacean Sensory Systems.

Cetaceans have undergone profound sensory adaptations in response to their aquatic environment during evolution. These adaptations are characterised by anatomo-functional changes in the classically defined sensory systems, shaping their neuroanatomy accordingly. This review offers a concise and up-to-date overview of our current understanding of the neuroanatomy associated with cetacean sensory systems. It encompasses a wide spectrum, ranging from the peripheral sensory cells responsible for detecting environmental cues, to the intricate structures within the central nervous system that process and interpret sensory information. Despite considerable progress in this field, numerous knowledge gaps persist, impeding a comprehensive and integrated understanding of their sensory adaptations, and through them, of their sensory perspective. By synthesising recent advances in neuroanatomical research, this review aims to shed light on the intricate sensory alterations that differentiate cetaceans from other mammals and allow them to thrive in the marine environment. Furthermore, it highlights pertinent knowledge gaps and invites future investigations to deepen our understanding of the complex processes in cetacean sensory ecology and anatomy, physiology and pathology in the scope of conservation biology.

Development of a Gustatory Function Test for Clinical Application in Korean Subjects

PURPOSE: To obtain validated clinical values suitable for developing a gustatory function test, including umami taste, in a Korean population. MATERIALS AND METHODS: The investigation involved 297 participants with self-reported normal sense of taste and smell. Liquid solutions were used for the assessment of gustatory function. The test consisted of 30 taste solutions [six concentrations of five tastants (sweet, bitter, salty, sour, and umami)]. For evaluation of overall gustatory function, the number of detected or correctly recognized taste thresholds was combined to form a “taste score.” RESULTS: Mean values of each detection and recognition threshold for the five tastes in men were consistently lower than those of women. The 10th percentile of taste score for recognition was used as the cut-off value for distinguishing normogeusia from hypogeusia. In subgroup analysis, total taste score from recognition thresholds revealed a significant negative correlation with age, indicating lower scores for increasing age. Taste score for non-smokers was significantly higher than that of smokers, in terms of detection and recognition of taste sensitivities. CONCLUSION: This gustatory function test was easy to perform, affordable, and time-saving, with the capacity to self-produce and obtain reliable data. Gustatory function was more sensitive in young people, women, and non-smokers.