Taste System Research Articles

Structural motifs for subtype-specific pH-sensitive gating of vertebrate otopetrin proton channels.

Otopetrin (OTOP) channels are proton-selective ion channels conserved among vertebrates and invertebrates, with no structural similarity to other ion channels. There are three vertebrate OTOP channels (OTOP1, OTOP2, and OTOP3), of which one (OTOP1) functions as a sour taste receptor. Whether extracellular protons gate OTOP channels, in addition to permeating them, was not known. Here, we compare the functional properties of the three murine OTOP channels using patch-clamp recording and cytosolic pH microfluorimetry. We find that OTOP1 and OTOP3 are both steeply activated by extracellular protons, with thresholds of pHo <6.0 and 5.5, respectively, and kinetics that are pH-dependent. In contrast, OTOP2 channels are broadly active over a large pH range (pH 5 pH 10) and carry outward currents in response to extracellular alkalinization (>pH 9.0). Strikingly, we could change the pH-sensitive gating of OTOP2 and OTOP3 channels by swapping extracellular linkers that connect transmembrane domains. Swaps of extracellular linkers in the N domain, comprising transmembrane domains 1-6, tended to change the relative conductance at alkaline pH of chimeric channels, while swaps within the C domain, containing transmembrane domains 7-12, tended to change the rates of OTOP3 current activation. We conclude that members of the OTOP channel family are proton-gated (acid-sensitive) proton channels and that the gating apparatus is distributed across multiple extracellular regions within both the N and C domains of the channels. In addition to the taste system, OTOP channels are expressed in the vertebrate vestibular and digestive systems. The distinct gating properties we describe may allow them to subserve varying cell-type specific functions in these and other biological systems.

A glucokinase-linked sensor in the taste system contributes to glucose appetite

ObjectivesDietary glucose is a robust elicitor of central reward responses and ingestion, but the key peripheral sensors triggering these orexigenic mechanisms are not entirely known. The objective of this study was to determine whether glucokinase, a phosphorylating enzyme with known glucosensory roles, is also expressed in taste bud cells and contributes to the immediate hedonic appeal of glucose-containing substances. Methods and resultsGlucokinase (GCK) gene transcripts were localized in murine taste bud cells with RNAScope®, and GCK mRNA was found to be upregulated in the circumvallate taste papillae in response to fasting and after a period of dietary access to added simple sugars in mice, as determined with real time-qPCR. Pharmacological activation of glucokinase with Compound A increased primary taste nerve and licking responses for glucose but did not impact responsivity to fructose in naïve mice. Virogenetic silencing of glucokinase in the major taste fields attenuated glucose-stimulated licking, especially in mice that also lacked sweet receptors, but did not disrupt consummatory behaviors for fructose or the low-calorie sweetener, sucralose in sugar naïve mice. Knockdown of lingual glucokinase weakened the acquired preference for glucose over fructose in sugar-experienced mice in brief access taste tests. ConclusionsCollectively, our data establish that glucokinase contributes to glucose appetition at the very first site of nutrient detection, in the oral cavity. The findings expand our understanding of orosensory inputs underlying nutrition, metabolism, and food reward.

A Taste Bud Organoid-Based Microelectrode Array Biosensor for Taste Sensing

The biological taste system has the unique ability to detect taste substances. Biomaterials originating from a biological taste system have been recognized as ideal candidates to serve as sensitive elements in the development of taste-based biosensors. In this study, we developed a taste bud organoid-based biosensor for the research of taste sensation. Taste bud organoids prepared from newborn mice were cultured and loaded onto the surface of a 64-channel microelectrode array (MEA) chip to explore the electrophysiological changes upon taste; an MEA chip was used to simultaneously record multiple-neuron firing activities from taste bud organoids under different taste stimuli, which helped to reveal the role of taste buds in taste sensing. The obtained results show that taste cells separated from the taste epithelium grew well into spherical structures under 3D culture conditions. These structures were composed of multiple cells with obvious budding structures. Moreover, the multicellular spheres were seeded on a 64-channel microelectrode array and processed with different taste stimuli. It was indicated that the MEA chip could efficiently monitor the electrophysiological signals from taste bud organoids in response to various taste stimuli. This biosensor provides a new method for the study of taste sensations and taste bud functions.

Biohybrid Tongue for Evaluation of Taste Interaction between Sweetness and Sourness

The past decade has witnessed tremendous progress achieved in taste research, while few studies focus on interactions among taste compounds. Indeed, sweeteners and acidulants are commonly used food additives, and sweet-sour mixtures always provide improved tastes. For example, sensory studies have shown that sourness suppresses sweetness. However, the degree of sweetness suppression by sourness is difficult to evaluate quantitatively and objectively. Therefore, we propose a biohybrid tongue that is constructed by integrating mammalian gustatory epithelium with a microelectrode array chip. The taste quality and intensity information is coded in time-frequency patterns of local field potential. Different response patterns evoked by sweet and sour stimuli are observed, and the response is dose-dependent. Then, interaction effects of sourness against sweetness are quantified. The results indicate that suppression of sweetness by sourness occurs by increasing sourness concentrations. In summary, this study provides a powerful new tool for quantitative evaluation of sweet, sour, and their binary taste interactions that mimic the mammalian taste system.

Investigating New Sensory Methods Related to Taste Sensitivity, Preferences, and Diet of Mother-Infant Pairs and Their Relationship With Body Composition and Biomarkers: Protocol for an Explorative Study.

BackgroundEarly experiences with different flavors play an important role in infant development, including food and taste acceptance. Flavors are already perceived in utero with the development of the taste and olfactory system and are passed on to the child through breast and bottle feeding. Therefore, the first 1000 days of life are considered a critical window for infant developmental programming.ObjectiveThe objective of our study is to investigate, both in the prenatal and postnatal period, taste sensitivity, preferences, and dietary diversity of mother-infant pairs. The explorative study design will also report on the impact of these variables on body composition (BC) and biomarkers. In contrast to conventional methods, this study involves long-term follow-up data collection from mother-infant pairs; moreover, the integration of audiovisual tools for recording infants' expressions pertaining to taste stimuli is a novelty of this study. Considering these new methodological approaches, the study aims to assess taste-related data in conjunction with BC parameters like fat-free mass or fat mass, biomarkers, and nutritional intake in infants and children.MethodsHealthy pregnant women aged between 18 and 50 years (BMI≥18.5 kg/m2 to ≤30 kg/m2; <28 weeks of gestation) were recruited from January 2014 to October 2014. The explorative design implies 2 center visits during pregnancy (24-28 weeks of gestation and 32-34 weeks of gestation) and 2 center visits after delivery (6-8 weeks postpartum and 14-16 weeks postpartum) as well as follow-up visits at 1, 3-3.5, and 6 years after delivery. Data collection encompasses anthropometric and biochemical measurements as well as BC analyses with air displacement plethysmography, taste perception assessments, and multicomponent questionnaires on demographics, feeding practices, and nutritional and lifestyle behaviors. Audiovisual data from infants’ reactions to sensory stimuli are collected and coded by trained staff using Baby Facial Action Coding and the Body Action Posture System. Birth outcomes and weight development are obtained from medical records, and additional qualitative data are gathered from 24 semistructured interviews.ResultsOur cohort represents a homogenous group of healthy women with stringent exclusion criteria. A total of 54 women met the eligibility criteria, whereas 47 mother-child pairs completed data collection at 4 center visits during and after pregnancy. Follow-up phases, data analyses, and dissemination of the findings are scheduled for the end of 2023. The study was approved by the ethics committee of the Medical University of Graz (EC No 26–066 ex 13/14), and all participants provided informed consent.ConclusionsThe results of this study could be useful for elucidating the connections between maternal and infant statuses regarding diet, taste, biomarkers, and prenatal and postnatal weight development. This study may also be relevant to the establishment of further diagnostic and interventional strategies targeting childhood obesity and early body fat development.International Registered Report Identifier (IRRID)DERR1-10.2196/37279

Serotonergic fast lane from taste detection to preparatory digestive actions

Nutrient detection through the taste system triggers various physiological changes in the body. In this issue of Neuron, Yao and Scott (2022) identify two distinct classes of serotonergic neurons in Drosophila that transform sweet and bitter taste signals into endocrine and digestive responses.

A functional division of Drosophila sweet taste neurons that is value-based and task-specific

Sucrose is an attractive feeding substance and a positive reinforcer for Drosophila But Drosophila females have been shown to robustly reject a sucrose-containing option for egg-laying when given a choice between a plain and a sucrose-containing option in specific contexts. How the sweet taste system of Drosophila promotes context-dependent devaluation of an egg-laying option that contains sucrose, an otherwise highly appetitive tastant, is unknown. Here, we report that devaluation of sweetness/sucrose for egg-laying is executed by a sensory pathway recruited specifically by the sweet neurons on the legs of Drosophila First, silencing just the leg sweet neurons caused acceptance of the sucrose option in a sucrose versus plain decision, whereas expressing the channelrhodopsin CsChrimson in them caused rejection of a plain option that was "baited" with light over another that was not. Analogous bidirectional manipulations of other sweet neurons did not produce these effects. Second, circuit tracing revealed that the leg sweet neurons receive different presynaptic neuromodulations compared to some other sweet neurons and were the only ones with postsynaptic partners that projected prominently to the superior lateral protocerebrum (SLP) in the brain. Third, silencing one specific SLP-projecting postsynaptic partner of the leg sweet neurons reduced sucrose rejection, whereas expressing CsChrimson in it promoted rejection of a light-baited option during egg-laying. These results uncover that the Drosophila sweet taste system exhibits a functional division that is value-based and task-specific, challenging the conventional view that the system adheres to a simple labeled-line coding scheme.

Three-dimensional characteristic of fungiform papillae and its taste buds in European bison (Bison bonasus), cattle (Bos taurus), and Bison bonasus hybrid

BackgroundOur recent macro- and scanning electron microscopic study of tongue conducted on domesticated cattle, wild living European bison, and Bison bonasus hybrid revealed various spatial arrangement and number of gustatory and mechanical papillae between parental species and their hybrid. Furthermore, scanning electron microscopy analysis of gustatory papillae indicated the variable distribution of fungiform papillae (Fu) over the surface of the tongue, which could be significant in differentiated taste perception during feeding in studied wild living and domesticated husbandry ruminants. To specify the detailed microstructure of Fu papillae with connective tissue cores (CTC) and intraepithelial taste buds system, the first time the three-dimensional computer-aided analysis of serial histoslides resulted in the rendering of 3D reconstructions of Fu papillae.ResultsThe comparative analysis of 3D models Fu papillae conducted in six areas of lingual mucosa of each tongue revealed information about, microstructural diversity of Fu papillae in studied ruminants. The estimation of number and density of Fu papillae on tongues, rate of protrusion of papillae over mucosa, and a number of taste buds per papilla allowed to state the ventral surface of the lingual apex and posterolateral surfaces of the lingual torus as regions important in taste perception, as in the preselection of taken food, as well in the analysis of food during rumination, respectively. On the 3D models were observed three structural types of CTC of different distribution on the tongue in studied species. The quantitative data of the number of taste buds on Fu papillae have regional functional differences in the taste system important in feeding and veterinary practice. Moreover, our analysis determined specific features in examined hybrid and showed similarities of some studied features with cattle, i.e., maternal species.ConclusionsThe 3D reconstruction method used for the first time in the field of study of the lingual papillae and taste buds system can be considered as an innovative and effective tool in assessing of the microstructures of Fu papillae, and it could be suitable for further studies of taste system structures in normal and pathological condition.

Understanding responses to chemical mixtures: looking forward from the past.

Our goal in this article is to provide a perspective on how to understand the nature of responses to chemical mixtures. In studying responses to mixtures, researchers often identify "mixture interactions"-responses to mixtures that are not accurately predicted from the responses to the mixture's individual components. Critical in these studies is how to predict responses to mixtures and thus to identify a mixture interaction. We explore this issue with a focus on olfaction and on the first level of neural processing-olfactory sensory neurons-although we use examples from taste systems as well and we consider responses beyond sensory neurons, including behavior and psychophysics. We provide a broadly comparative perspective that includes examples from vertebrates and invertebrates, from genetic and nongenetic animal models, and from literature old and new. In the end, we attempt to recommend how to approach these problems, including possible future research directions.

Interactions of umami with the four other basic tastes in equi-intense aqueous solutions

Previous research has shown that the addition of equi-intense concentrations of taste compounds leads to mixture suppression, with sweetness being the least suppressed taste while being the strongest suppressor of the other taste stimuli. However, perceived intensity of umami (savoury taste) within complex mixtures is less defined. Since maintaining savoury taste of foods at reduced salt levels is a growing need, this study investigated the role of umami in complex taste systems. Initially the concentrations of single tastants were adjusted until a trained sensory panel rated them as equi-intense using general labelled magnitude scales (gLMS). In order to evaluate the impact of umami taste on other tastes, and vice versa, three sample sets were prepared as binary and quinary systems. The first two sets utilised monosodium glutamate (MSG) as the umami tastant; one set without balancing the sodium level in MSG and another set accounting for it by the addition of sodium at an equivalent molarity. The third set used monopotassium L-glutamate monohydrate (MPG) as the source of umami to overcome the confounding influence of sodium. All samples were rated by trained sensory panellists. The results of the three studies conclude that umami taste does not enhance or suppress the perception of any other taste in binary aqueous taste systems (p > 0.05); whereas sweet, salty, sour and bitter significantly suppress the perception of umami in both binary and quinary systems (p < 0.05). Where glutamate and sodium chloride were used together, both umami and salty taste were maintained.

Purinergic neurotransmission in the gustatory system.

Taste buds consist of specialized epithelial cells which detect particular tastants and synapse onto the afferent taste nerve innervating the endorgan. The nature of the neurotransmitter released by taste cells onto the nerve fiber was enigmatic early in this century although neurotransmitters for other sensory receptor cell types, e.g. hair cells, photoreceptors, was known for at least a decade. A 1999 paper by Burnstock and co-workers (Bo et al., 1999) showing the presence of P2X receptors on the afferent nerves served as a springboard for research that ultimately led to the discovery of ATP as the crucial neurotransmitter in the taste system (Finger et al., 2005). Subsequent work showed that a subpopulation of taste cells utilize a unique release channel, CALHM1/3, to release ATP in a voltage-dependent manner. Despite these advances, several aspects of purinergic transmission in this system remain to be elucidated.

Field-Effect Sensors Using Biomaterials for Chemical Sensing.

After millions of years of evolution, biological chemical sensing systems (i.e., olfactory and taste systems) have become very powerful natural systems which show extreme high performances in detecting and discriminating various chemical substances. Creating field-effect sensors using biomaterials that are able to detect specific target chemical substances with high sensitivity would have broad applications in many areas, ranging from biomedicine and environments to the food industry, but this has proved extremely challenging. Over decades of intense research, field-effect sensors using biomaterials for chemical sensing have achieved significant progress and have shown promising prospects and potential applications. This review will summarize the most recent advances in the development of field-effect sensors using biomaterials for chemical sensing with an emphasis on those using functional biomaterials as sensing elements such as olfactory and taste cells and receptors. Firstly, unique principles and approaches for the development of these field-effect sensors using biomaterials will be introduced. Then, the major types of field-effect sensors using biomaterials will be presented, which includes field-effect transistor (FET), light-addressable potentiometric sensor (LAPS), and capacitive electrolyte–insulator–semiconductor (EIS) sensors. Finally, the current limitations, main challenges and future trends of field-effect sensors using biomaterials for chemical sensing will be proposed and discussed.

Dietary Macronutrient Imbalances Lead to Compensatory Changes in Peripheral Taste via Independent Signaling Pathways.

Food choice, in animals, has been known to change with internal nutritional state and also with variable dietary conditions. To better characterize mechanisms of diet-induced plasticity of food preference in Drosophila melanogaster, we synthesized diets with macronutrient imbalances and examined how food choice and taste sensitivity were modified in flies that fed on these diets. We found that dietary macronutrient imbalances caused compensatory behavioral shifts in both sexes to increase preference for the macronutrient that was scant in the food source, and simultaneously reduce preference for the macronutrient that was enriched. Further analysis with females revealed analogous changes in sweet taste responses in labellar neurons, with increased sensitivity on sugar-reduced diet and decreased sensitivity on sugar-enriched diet. Interestingly, we found differences in the onset of changes in taste sensitivity and behavior, which occur over 1-4 d, in response to dietary sugar reduction or enrichment. To investigate molecular mechanisms responsible for diet-induced taste modulation, we used candidate gene and transcriptome analyses. Our results indicate that signaling via Dop2R is involved in increasing cellular and behavioral sensitivity to sugar as well as in decreasing behavioral sensitivity to amino acids on dietary sugar reduction. On the other hand, cellular and behavioral sensitivity to sugar relies on dilp5 and a decrease in sugar preference following dietary sugar abundance was correlated with downregulation of dilp5 Together, our results suggest that feeding preference for sugar and amino acid can be modulated independently to facilitate food choice that accounts for prior dietary experience.SIGNIFICANCE STATEMENT Animals adjust their feeding preferences based on prior dietary experiences. Here, we find that upon dietary macronutrient deprivation, flies undergo compensatory changes in food preference. The altered preference correlates with changes in peripheral taste sensitivity. While Dop2R mediates changes following dietary sugar reduction, downregulation of dilp5 is associated with changes caused by a sugar-enriched diet. This study contributes to a better understanding of neurophysiological plasticity of the taste system in flies, and its role in facilitating adjustment of foraging behavior based on nutritional requirements.

Individual bitter-sensing neurons in Drosophila exhibit both ON and OFF responses that influence synaptic plasticity

The brain generates internal representations that translate sensory stimuli into appropriate behavior. In the taste system, different tastes activate distinct populations of sensory neurons. We investigated the temporal properties of taste responses in Drosophila and discovered that different types of taste sensory neurons show striking differences in their response dynamics. Strong responses to stimulus onset (ON responses) and offset (OFF responses) were observed in bitter-sensing neurons in the labellum, whereas bitter neurons in the leg and other classes of labellar taste neurons showed only an ON response. Individual labellar bitter neurons generate both ON and OFF responses through a cell-intrinsic mechanism that requires canonical bitter receptors. A single receptor complex likely generates both ON and OFF responses to a given bitter ligand. These ON and OFF responses in the periphery are propagated to dopaminergic neurons that mediate aversive learning, and the presence of the OFF response impacts synaptic plasticity when bitter is used as a reinforcement cue. These studies reveal previously unknown features of taste responses that impact neural circuit function and may be important for behavior. Moreover, these studies show that OFF responses can dramatically influence timing-based synaptic plasticity, which is thought to underlie associative learning.

Chemosensory Gene Expression for Two Closely Relative Species Rhodnius robustus and R. prolixus (Hemiptera, Reduviidade, Triatominae) Vectors of Chagas Disease

Two closely related species, Rhodnius prolixus and Rhodnius robustus, are the vectors of Trypanosoma cruzi, which is the causative agent of Chagas disease, but clearly exhibit clear-cut differences in their ecological behavior. R. prolixus is considered as a domiciliated species, whereas R. robustus only sporadically visits human houses in Amazonia. We performed a chemosensory gene expression study via RNA-sequencing (RNA-seq) for the two species and also included a laboratory introgressed R. robustus strain. We built an assembled transcriptome for each sample and for both sexes and compiled all in a reference transcriptome for a differential gene expression study. Because the genes specifically expressed in one condition and not expressed in another may also reflect differences in the adaptation of organisms, a comparative study of the presence/absence of transcripts was also performed for the chemosensory transcripts, namely chemosensory proteins (CSPs), odorant-binding proteins (OBPs), odorant receptors (ORs), gustatory receptors (GRs), and ionotropic receptors (IRs), as well as takeout (TO) transcripts because TO proteins have been proposed to be associated with chemosensory perception in both olfactory and taste systems. In this study, 12 novel TO transcripts from the R. prolixus genome were annotated. Among the 199 transcripts, out of interest, annotated in this study, 93% were conserved between R. prolixus and the sylvatic R. robustus. Moreover, 10 transcripts out of interest were specifically expressed in one sex and absent in another. Three chemosensory transcripts were found to be expressed only in the reared R. prolixus (CSP19, OBP9, and OR89) and only one in sylvatic R. robustus (OR22). A large set of transcripts were found to be differentially expressed (DE) between males and females (1,630), with a majority of them (83%) overexpressed in males. Between environmental conditions, 8,596 transcripts were DE, with most (67%) overexpressed in the sylvatic R. robustus samples, including 17 chemosensory transcripts (4 CSPs, 1 OBP, 5 ORs, 1 GR, 4 IR, and 2 TO), but 4 genes (OBP19, OR13, OR40, and OR79) were overexpressed in the reared samples.

Physiology of Taste Processing in the Tongue, Gut, and Brain.

The gustatory system detects and informs us about the nature of various chemicals we put in our mouth. Some of these have nutritive value (sugars, amino acids, salts, and fats) and are appetitive and avidly ingested, whereas others (atropine, quinine, nicotine) are aversive and rapidly rejected. However, the gustatory system is mainly responsible for evoking the perception of a limited number of qualities that humans taste as sweet, umami, bitter, sour, salty, and perhaps fat [free fatty acids (FFA)] and starch (malto-oligosaccharides). The complex flavors and mouthfeel that we experience while eating food result from the integration of taste, odor, texture, pungency, and temperature. The latter three arise primarily from the somatosensory (trigeminal) system. The sensory organs used for detecting and transducing many chemicals are found in taste buds (TBs) located throughout the tongue, soft palate esophagus, and epiglottis. In parallel with the taste system, the trigeminal nerve innervates the peri-gemmal epithelium to transmit temperature, mechanical stimuli, and painful or cooling sensations such as those produced by changes in temperature as well as from chemicals like capsaicin and menthol, respectively. This article gives an overview of the current knowledge about these TB cells' anatomy and physiology and their trigeminal induced sensations. We then discuss how taste is represented across gustatory cortices using an intermingled and spatially distributed population code. Finally, we review postingestion processing (interoception) and central integration of the tongue-gut-brain interaction, ultimately determining our sensations as well as preferences toward the wholesomeness of nutritious foods. © 2021 American Physiological Society. Compr Physiol 11:1-35, 2021.

Sprague Dawley Rats Gaining Weight on a High Energy Diet Exhibit Damage to Taste Tissue Even after Return to a Healthy Diet.

Many reports detail taste dysfunction in humans and animals with obesity. For example, mice consuming an obesogenic diet for a short period have fewer taste buds than their lean littermates. Further, rats with diet-induced obesity (DIO) show blunted electrophysiological responses to taste in the brainstem. Here, we studied the effects of high energy diet (HED)-induced peripheral taste damage in rats, and whether this deficiency could be reversed by returning to a regular chow diet. Separate groups of rats consumed a standard chow diet (Chow), a HED for 10 weeks followed by a return to chow (HED/chow), or a HED for 10 weeks followed by a restricted HED that was isocaloric with consumption by the HED/chow group (HED/isocal). Fungiform taste papilla (FP) and circumvallate taste bud abundance were quantified several months after HED groups switched diets. Results showed that both HED/chow and HED/isocal rats had significantly fewer FP and lower CV taste bud abundance than control rats fed only chow. Neutrophil infiltration into taste tissues was also quantified, but did not vary with treatment on this timeline. Finally, the number of cells undergoing programmed cell death, measured with caspase-3 staining, inversely correlated with taste bud counts, suggesting taste buds may be lost to apoptosis as a potential mechanism for the taste dysfunction observed in obesity. Collectively, these data show that DIO has lasting deleterious effects on the peripheral taste system, despite a change from a HED to a healthy diet, underscoring the idea that obesity rather than diet predicts damage to the taste system.

Preliminary Research into the Sustainable Responsibility of Teaware Design—A Fs/QCA Analysis of the Influence of the Smell and Taste of Tea through Visual and Tactile Perception

Most studies concerned with sustainable design issues focus on product design to change user behavior, increase the product lifespan, reduce energy waste, or employ the user experience to influence the behavior of other users. Rarely do they discuss how to design products that meet the real needs of consumers and reduce design waste and excessive consumption. Teaware designers and producers have invisibly created a considerable carbon footprint with regard to nonrenewable clay and energy waste due to excessive production. Therefore, this research uses visual and tactile research into the Chinese drinking cup to integrate user experience and the designer’s thinking and methods to ensure the sustainable value of the design and industry. This research uses experimental methods to collect and analyze the data with a fuzzy set qualitative comparative analysis (fs/QCA). The research found that the visual, tactile, and sensory perceptions of general consumers and tea professionals have different influencing factors on the taste system. This research provides evidence that the size of the tea-drinking container and the thickness of the cup’s rim will affect the perception of the tea’s taste and smell. This research provides new thinking for the design of Chinese tea-drinking utensils. It could solve social problems and dilemmas through design and contribute to the sustainable development of the design.

The attractive effects of amino acids and some classical substances on grass carp (Ctenopharyngodon idellus).

Grass carp (Ctenopharyngodon idellus) is one of the most essential fishing species in China. The bait for this fish is rapidly developing. However, the study on the attractants in the bait for this fish lacks. This study was designed to systematically investigate the effects of 16 kinds of test substances on the perspective of behaviour and physiology of grass carp by using different kinds of methods, including behavioral tests (maze test and biting-balls test) and electro-olfactogram (EOG). Our experiment's idea is mainly to imitate: in addition to vision, fish in nature also use smell to find food and finally swallow under the action of olfaction, taste, and other sensory systems. Firstly, the behavioral maze test was used to screen the attractive or suppressive effect of 16 test substances on grass carp, and the electronic olfactory recording method was used to further evaluate the olfactory response of grass carp to the eight stimuli selected from the maze test. Then, the best concentrations of these eight stimuli and their combination were investigated by the biting-balls test to compound a formula with the strongest appetite for grass carp. The results of behavioral maze test showed that dimethyl-β-propiothetin (DMPT), dimethylthetin (DMT), glycine, taurine, L-glutamic, L-alanine, L-proline, and L-arginine have different degrees of usefulness in attracting grass carp. The electro-olfactogram recoding showed that the EOG response of grass carp to the stimuli is a transient biphasic potential change and all of the eight stimuli could induce the EOG response of grass carp. The biting-balls test showed that glycine, L-glutamic, and L-arginine at 10-2mol/L had significant feeding stimulation and DMT at 10-1mol/L had significant feeding stimulation than the other groups. Finally, formula 9 composed of DMT, glycine, L-glutamic acid, and L-arginine has the greatest attraction for grass carp. The results of this study verified the attractive effect of some amino acids and other chemicals on grass carp fishing, and would provide support for the production of specific grass carp attractants.

Effects of NPF on larval taste responses and feeding behaviors in Ostrinia furnacalis

The insect taste system regulates insect feeding behavior and patterns of food consumption. In this study, we showed that the medial and lateral sensilla styloconica in the mouthparts of 5th-instar Asian corn borer larvae are sensitive to fructose and sucrose in a concentration-dependent way. The two sensilla produced significant electrophysiological responses (greater than100 spikes/s) by exposure to 10 mM fructose or sucrose. However, electrophysiological responses and feeding preferences to fructose or sucrose were inhibited by neuropeptide F double-stranded RNA (dsNPF). Additionally, the medial sensilla styloconica are sensitive to low concentrations of the deterrents caffeine and nicotine. However, starvation, followed by increases in larval npf expression plus feeding, led to increases in spike frequencies of related sensilla to fructose, sucrose, and deterrents. In contrast, these responses were reduced on the dsNPF treatment. Our results suggest that NPF plays an important role influencing caterpillar feeding behavior through regulating the taste neurons of the sensilla styloconica.