Taste Information Research Articles

Local field potentials in the gustatory cortex carry taste information.

It has been recently shown that local field potentials (LFPs) from the auditory and visual cortices carry information about sensory stimuli, but whether this is a universal property of sensory cortices remains to be determined. Moreover, little is known about the temporal dynamics of sensory information contained in LFPs following stimulus onset. Here we investigated the time course of the amount of stimulus information in LFPs and spikes from the gustatory cortex of awake rats subjected to tastants and water delivery on the tongue. We found that the phase and amplitude of multiple LFP frequencies carry information about stimuli, which have specific time courses after stimulus delivery. The information carried by LFP phase and amplitude was independent within frequency bands, since the joint information exhibited neither synergy nor redundancy. Tastant information in LFPs was also independent and had a different time course from the information carried by spikes. These findings support the hypothesis that the brain uses different frequency channels to dynamically code for multiple features of a stimulus.

Origin of Palatability Coding in Medial Prefrontal Cortex

Gustatory processing starts with activation of taste receptors located in the oral cavity. Axons of these receptor cells project to the primary gustatory nucleus in the brainstem, and from there to the pons. In the following stage, taste information flows in two independent channels: through the

The Role of Tight Junctions and Hypertonicity in Taste Information Processing

Many scientists have investigated taste nerve responses without regarding the tonicity of taste stimulating solutions that varies in a wide range. We increased the tonicity by adding nonelectrolytes that elicited no taste nerve responses in bullfrogs, and investigated hypertonicity effects on the taste nerve responses to inorganic salts and bitter substances. Here, we show that the hypertonicity opens tight junctions surrounding taste receptor cells and changes the magnitude and firing pattern of taste nerve responses. We quantitatively suggest that the changes result from the magnitude and direction of local circuit currents generated by diffusion potentials across the tight junctions.

The neuronal and molecular basis of quinine-dependent bitter taste signaling in Drosophila larvae

The sensation of bitter substances can alert an animal that a specific type of food is harmful and should not be consumed. However, not all bitter compounds are equally toxic and some may even be beneficial in certain contexts. Thus, taste systems in general may have a broader range of functions than just in alerting the animal. In this study we investigate bitter sensing and processing in Drosophila larvae using quinine, a substance perceived by humans as bitter. We show that behavioral choice, feeding, survival, and associative olfactory learning are all directly affected by quinine. On the cellular level, we show that 12 gustatory sensory receptor neurons that express both GR66a and GR33a are required for quinine-dependent choice and feeding behavior. Interestingly, these neurons are not necessary for quinine-dependent survival or associative learning. On the molecular receptor gene level, the GR33a receptor, but not GR66a, is required for quinine-dependent choice behavior. A screen for gustatory sensory receptor neurons that trigger quinine-dependent choice behavior revealed that a single GR97a receptor gene expressing neuron located in the peripheral terminal sense organ is partially necessary and sufficient. For the first time, we show that the elementary chemosensory system of the Drosophila larva can serve as a simple model to understand the neuronal basis of taste information processing on the single cell level with respect to different behavioral outputs.

Thalamic Input to Representations of the Teeth, Tongue, and Face in Somatosensory Area 3b of Macaque Monkeys

Representations of the parts of the oral cavity and face in somatosensory area 3b of macaque monkeys were identified with microelectrode recordings and injected with different neuroanatomical tracers to reveal patterns of thalamic projections to tongue, teeth, and other representations in primary somatosensory cortex. The locations of injection sites and resulting labeled neurons were further determined by relating sections processed to reveal tracers to those processed for myeloarchitecture in the cortex and multiple architectural stains in the thalamus. The ventroposterior medial subnucleus (VPM) for touch was identified as separate from the ventroposterior medial parvicellular nucleus (VPMpc) for taste by differential expression of several types of proteins. Our results revealed somatotopically matched projections from VPM to the part of 3b representing intra-oral structures and the face. Retrogradely labeled cells resulting from injections in area 3b were also found in other thalamic nuclei including: anterior pulvinar (Pa), ventroposterior inferior (VPI), ventroposterior superior (VPS), ventroposterior lateral (VPL), ventral lateral (VL), center median (CM), central lateral (CL), and medial dorsal (MD). None of our injections, including those into the representation of the tongue, labeled neurons in VPMpc, the thalamic taste nucleus. Thus, area 3b does not appear to be involved in processing taste information from the thalamus. This result stands in contrast to those reported for New World monkeys.

Role of the ectonucleotidase NTPDase2 in taste bud function

Taste buds are unusual in requiring ATP as a transmitter to activate sensory nerve fibers. In response to taste stimuli, taste cells release ATP, activating purinergic receptors containing the P2X2 and P2X3 subunits on taste nerves. In turn, the released ATP is hydrolyzed to ADP by a plasma membrane nucleoside triphosphate previously identified as nucleoside triphosphate diphosphohydrolase-2 (NTPDase2). In this paper we investigate the role of this ectonucleotidase in the function of taste buds by examining gene-targeted Entpd2-null mice globally lacking NTPDase2. RT-PCR confirmed the absence of NTPDase2, and ATPase enzyme histochemistry reveals no reaction product in taste buds of knockout mice, suggesting that NTPDase2 is the dominant form in taste buds. RT-PCR and immunocytochemistry demonstrated that in knockout mice all cell types are present in taste buds, even those cells normally expressing NTPDase2. In addition, the overall number and size of taste buds are normal in Entpd2-null mice. Luciferin/luciferase assays of circumvallate tissue of knockout mice detected elevated levels of extracellular ATP. Electrophysiological recordings from two taste nerves, the chorda tympani and glossopharyngeal, revealed depressed responses to all taste stimuli in Entpd2-null mice. Responses were more depressed in the glossopharyngeal nerve than in the chorda tympani nerve and involved all taste qualities; responses in the chorda tympani were more depressed to sweet and umami stimuli than to other qualities. We suggest that the excessive levels of extracellular ATP in the Entpd2-knockout animals desensitize the P2X receptors associated with nerve fibers, thereby depressing taste responses.

Information processing in brainstem bitter taste-relaying neurons defined by genetic tracing

Bitter reception is mediated by taste receptor cells that coexpress multiple T2Rs, a family of G-protein-coupled receptors. However, it remains elusive how bitter taste information is translated in the brain into appropriate behavioral responses. Here we used a combination of genetic tracing and electrophysiological and immunohistochemical analyses in mice to functionally characterize the neurons in the solitary tract nuclei of the medulla, which receive input from mT2R5-expressing cells. The neurons defined by a transneuronal tracer originating from mT2R5-expressing cells receive glutamatergic synaptic input via the AMPA receptor. The satiety peptide cholecystokinin increases glutamatergic transmission, suggesting an interaction between information processing of taste and the homeostatic control of feeding. Nevertheless, the tracer-labeled neuron types are heterogeneous, and can be classified into catecholamine and pro-opiomelanocortin neurons. Our data reveal that the architectural solution in the first-order central relay that processes information from mT2R5-expressing cells uses unique ensembles of neurons with different neurotransmitters.

Taste Familiarity Is Inversely Correlated with Arc/Arg3.1 Hemispheric Lateralization

Biochemical, electrophysiological, and imaging studies suggest that the anterior part of the insular cortex (IC) serves as primary taste cortex, whereas fMRI studies in human propose that the anterior IC is also involved in processing of general novelty or saliency information. Here, we compared activity regulated cytoskeleton associated protein (Arc)/Arg3.1 protein levels in the rat IC following administration of familiar versus novel tastes. Surprisingly, there was no correlation between novel taste and Arc/Arg3.1 levels when measured as the sum of both left and right insular cortices. However, when left and right IC were examined separately, Arc/Arg3.1 level was lateralized following novel taste learning. Moreover, Arc/Arg3.1 lateralization was inversely correlated with taste familiarity, whereas the high lateralization of Arc/Arg3.1 expression observed following novel taste learning is reduced proportionally to the increment in taste familiarity. In addition, unilateral inhibition of protein synthesis in the IC had asymmetrical effect on memory, inducing strong memory impairment similarly to bilateral inhibition or memory preservation, indicating that hemispheric lateralization is central for processing taste saliency information. These results provide indications, at the gene level of expression, for the role of IC lateralization in processing novel taste information and for the asymmetrical contribution of protein synthesis in each hemisphere during memory consolidation.

Gene Network Analysis in Amygdala following Taste Aversion Learning in Rats.

Conditioned taste aversion (CTA) is an adaptive behavior that benefits survival of animals including humans and also serves as a powerful model to study the neural mechanisms of learning. Memory formation is a necessary component of CTA learning and involves neural processing and regulation of gene expression in the amygdala. Many studies have been focused on the identification of intracellular signaling cascades involved in CTA, but not late responsive genes underlying the long-lasting behavioral plasticity. In this study, we explored in silico experiments to identify persistent changes in gene expression associated with CTA in rats. We used oligonucleotide microarrays to identify 248 genes in the amygdala regulated by CTA. Pathway Studio and IPA software analyses showed that the differentially expressed genes in the amygdala fall in diverse functional categories such as behavior, psychological disorders, nervous system development and function, and cell-to-cell signaling. Conditioned taste aversion is a complex behavioral trait which involves association of visceral and taste inputs, consolidation of taste and visceral information, memory formation, retrieval of stored information, and extinction phase. In silico analysis of differentially expressed genes is therefore necessary to manipulate specific phase/stage of CTA to understand the molecular insight.

The lateralization of gustatory function and the flow of information from tongue to cortex

Controversy surrounds whether crossed and/or uncrossed fibers carry taste information from tongue to cortex and whether there is hemispheric specialization for gustatory processing. The current study examined these issues in 14 patients with unilateral insula lesions, seven with right-sided and seven with left-sided damage, and in 42 healthy controls. Two tasks were carried out, with tastants applied unilaterally to the tongue tip: (1) taste discrimination; and (2) stimulus sampling followed by judgments of quality, intensity, hedonics and name-recognition, for sweet, salty, bitter and sour tastants. Controls were better at discriminating tastants applied to their right tongue tip relative to their left, and better at taste quality judgments when tastants were applied to their left tongue tip relative to their right. Insula lesions to the left or right side resulted in bilateral impairments in discrimination, quality judgments and naming, when compared to controls. However, the Left insula group was poorer on tasks involving salt, and for ipsilateral hedonic judgments, relative to controls and the Right insula group. These findings are consistent with gustatory information ascending from tongue to cortex both ipsilaterally and contralaterally, and provide preliminary support for hemispheric gustatory specialization.

C-Fos-like Immunoreactivity in the nucleus of the solitary tract following taste stimulation of the contralateral side of the tongue

Taste receptors of the anterior tongue are innervated by the chorda tympani (CT) branch of the facial (VIIth) nerve. The CT nerve transmits information on taste to the ipsilateral nucleus of the solitary tract (NST), which is the first taste central nucleus in the medulla. Taste information is known to be transferred ipsilaterally along the taste pathway in the central nervous system. Some patients with unilateral CT damage often retain their ability to sense taste. This phenomenon is not explained by the unilateral taste pathway. We examined whether neurons in the NST receive information on taste from the contralateral side of the tongue by measuring c-Fos-like Immunoreactivity (cFLI) following taste stimulation of the contralateral side of the tongue in the anesthetized rats. We used four basic taste stimuli, 1.0 M sucrose, 0.3 M NaCl, 0.01 M citric acid, 0.03 M QHCl, and distilled water. Stimulation of one side of the tongue with taste stimuli induced cFLI in the NST bilaterally. The mean number of cFLI ranged from 23.28 ± 2.46 by contralateral QHCl to 30.28 ± 2.26 by ipsilateral NaCl stimulation. The difference between the number of cFLI in the ipsilaterl and contralateral NST was not significant. The result of the current study suggests that neurons in the NST receive information on taste not only from the ipsilateral but also the contralateral side of the tongue.

I’m Like You, Just Not In That Way: Tag Networks to Improve Collaborative Filtering

Collaborative filtering aims to predict a person’s preferences by examining the preferences of similar people. Many collaborative filtering algorithms rely on a coarse notion of similarity, which assumes that if two people are sufficiently simiar in a few specific areas, each is likely to make good recommendations for the other in most areas. Our trust in the opinions of others, though, is rarely absolute; we often tend to trust recommendations from certain people in certain areas. In this paper we develop an algorithm which reflects this notion. Rather than capturing taste information at the user level, we capture taste at the topic level by making use of tags: arbitrary words or phrases which are often used to group online content. Previous attempts to improve collaborative filtering using tag information have attempted to determine tag meanings, and as a result have depended upon complex semantic analyses. Our algorithm avoids these complications by focusing instead on the clusters which tags establish. Using tags in this way provides a significant improvement in the accuracy of recommendations without a commensurate loss in coverage. These tag clusters also give rise to networks which can be exploited to further improve recommendation results.

Automation Highlights from the Literature

Automation Highlights from the Literature

Development of a Taste-Masked Orodispersible Film Containing Dimenhydrinate

Orodispersible dosage forms are promising new approaches for drug delivery. They enable an easy application, as there is no need to drink high amounts of liquids or swallow large solid dosage forms. The aim of the study was to develop an orodispersible film (ODF) as an alternative to tablets, syrups or suppositories for the treatment of vomiting and nausea, especially for the pediatric population. Formulations were investigated by X-ray diffraction, scanning electron and polarized light microscopy. Additionally, two commercially available electronic taste sensing systems were used to investigate the applied taste-masking strategies. Results obtained from X-ray-diffraction and polarized light microscopy showed no recrystallization of dimenhydrinate in the formulation when cyclodextrin or maltodextrin were used as solubilizing and complexing agent. All ODFs showed fast disintegration depending on the characterization method. In order to get taste information, the dimenhydrinate formulations were analytically compared to pure drug and drug-free formulations by electronic tongues. Results obtained from both systems are comparable and were used together for the first time. It was possible to develop an ODF of dimenhydrinate that is fast disintegrating even in small volumes of liquid. Furthermore, in vitro taste assessment by two electronic tongues revealed taste-masking effects by the excipients.

Descending projections from the nucleus accumbens shell suppress activity of taste-responsive neurons in the hamster parabrachial nuclei

The parabrachial nuclei (PbN), the second central relay for the gustatory pathway, transfers taste information to various forebrain gustatory nuclei and to the gustatory cortex. The nucleus accumbens is one of the critical neural substrates of the reward system, and the nucleus accumbens shell region (NAcSh) is associated with feeding behavior. Taste-evoked neuronal responses of PbN neurons are modulated by descending projections from the gustatory nuclei in the forebrain. In the present study, we investigated whether taste-responsive neurons in the PbN project to the NAcSh and whether pontine gustatory neurons are subject to modulatory influence from the NAcSh in urethane-anesthetized hamsters. Extracellular single-unit activity was recorded in the PbN, and taste responses were confirmed by the delivery of 32 mM sucrose, NaCl, quinine hydrochloride, and 3.2 mM citric acid to the anterior tongue. The NAcSh was then stimulated (0.5 ms, ≤100 μA) bilaterally using concentric bipolar stimulating electrodes. A total of 98 taste neurons were recorded from the PbN. Eighteen neurons were antidromically invaded from the NAcSh, mostly the ipsilateral NAcSh (n = 16). Stimulation of the ipsilateral and contralateral NAcSh suppressed the neuronal activity of 88 and 55 neurons, respectively; 52 cells were affected bilaterally. In a subset of pontine neurons tested, electrical stimulation of the NAcSh during taste stimulation also suppressed taste-evoked neuronal firing. These results demonstrated that taste-responsive neurons in the PbN not only project to the NAcSh but also are under substantial descending inhibitory influence from the bilateral NAcSh.

Th e Role of Protein Phosphorylation in the Gustatory Cortex and Amygdala During Taste Learning

Protein phosphorylation and dephosphorylation form a major post-translation mechanism that enables a given cell to respond to ever-changing internal and external environments. Neurons, similarly to any other cells, use protein phosphorylation/dephosphorylation to maintain an internal homeostasis, but they also use it for updating the state of synaptic and intrinsic properties, following activation by neurotransmitters and growth factors. In the present review we focus on the roles of several families of kinases, phosphatases, and other synaptic-plasticity-related proteins, which activate membrane receptors and various intracellular signals to promote transcription, translation and protein degradation, and to regulate the appropriate cellular proteomes required for taste memory acquisition, consolidation and maintenance. Attention is especially focused on the protein phosphorylation state in two forebrain areas that are necessary for taste-memory learning and retrieval: the insular cortex and the amygdala. The various temporal phases of taste learning require the activation of appropriate waves of biochemical signals. These include: extracellular signal regulated kinase I and II (ERKI/II) signal transduction pathways; Ca2+-dependent pathways; tyrosine kinase/phosphatase-dependent pathways; brain-derived neurotrophicfactor (BDNF)-dependent pathways; cAMP-responsive element bindingprotein (CREB); and translation-regulation factors, such as initiation and elongation factors, and the mammalian target of rapamycin (mTOR). Interestingly, coding of hedonic and aversive taste information in the forebrain requires activation of different signal transduction pathways.

The Food Critic Who Couldn't Taste and 6 Other Cases of Dysgeusia in Multiple Sclerosis (P06.178)

Objective: Describe clinical, neuro-anatomic, and MRI correlates of dysgeusia (distortion of taste) in multiple sclerosis (MS). Background Dysgeusia is an uncommon symptom of MS; it may be underreported by patients and underappreciated by physicians. Taste sensation is conveyed by CN VII, IX, and X to the solitary tract/nucleus (medulla), up the ipsilateral central tegmental tract (pontine tegmentum), to the VPM thalamus, and on to the cortex. Given this, dysgeusia in an MS patient may portent an ipsilateral brainstem lesion. Design/Methods: Retrospective case series, consisting of seven patients presenting with dysgeusia to our MS center from 2007 to 2011. Clinical and MRI data was collected from electronic medical records. Results: A 40 yo man, a prominent food and wine critic, developed decrease in taste (hypogeusia) of his left tongue. He described utilizing the right side of his mouth “to get the taste information.” MRI identified a demyelinating lesion of the ipsilateral left brachium pontis and left cerebellar peduncle, plus other characteristic MS lesions. Hypogeusia resolved over 3 months. 15 months later, another brainstem relapse occurred resulting in disability. We present 6 additional cases with neuroimaging. Age ranged from 19 to 42. 4/7 were female. 4/7 experienced left sided hypogeusia and 3/7 experienced non-lateralized dysgeusia. Four of these attacks represented the initial demyelinating event, one of which was exclusively left hypogeusia. Dysgeusia lasted from 2 weeks to 3 months. Imaging revealed demyelinating lesions of left brachium pontis in 6/7 patients and right dorsal midbrain in one. 6/7 patients were diagnosed with relapsing remitting MS while one had CIS from a left brachium pontis lesion. Conclusions: Dysgeusia may be the initial presenting symptom of MS. Despite an excellent prognosis for symptomatic recovery, its presence indicates a brainstem attack, a known poor prognostic sign for MS. Patients with laterality to their hypogeusia had corresponding ipislateral brainstem demyelinating lesions. Disclosure: Dr. McGraw has received personal compensation for activities with Biogen Idec. Dr. Krieger has received personal compensation for activities with Acorda Therapeutics, Bayer HealthCare, Biogen Idec, Serono, Inc., Genzyme Corporation, Novartis, Teva Neuroscience as a consultant and/or participant on Pharmaceuticals Corporation. Dr. Wong has nothing to disclose. Dr. Fabian has received personal compensation for activities with Biogen Idec as a speaker.

A vision-taste interference model and the EEG measurement

Taste cognition can be interfered with by visual information, but the mechanism by which this happens has not been clarified. We assumed an interference model in the processes of taste and vision information. The model was tested with frequency analysis on EEG and using the switch response time. The tasks were matched/miss-matched between taste and vision information about orange juice and apple juice. There were changes in the ? waves that originated in the visual processing of a juice package, and changes in the β waves that originated in the taste processing. There is the possibility of a parallel processing mechanism in the vision-taste interference.

The event-related potential elicited by taste-visual cross-modal interference

Sixteen healthy subjects took part in this event-related potentials (ERPs) study aimed at investigating the neural response of the taste-visual cross-modal pairing. An interference effect was observed at the behavioral level: the mismatched condition was performed more slowly than the matched condition. ERP analyses revealed a more negative component between 400 and 600 ms in the mismatched condition than in the matched condition. Dipole source analysis of the difference wave (mismatched minus matched) indicated that two generators localized in prefrontal cortex (PFC) and posterior cingulate cortex (PCC) contributed to this cross-modal interference effect. These results provided the electrophysiological evidence of interference during the extraction of taste information from memory and conflict control during the incongruent taste-visual information processing.

Information about the taste stimulates choice of unfamiliar healthful food products

The present study aimed to assess whether taste information about unfamiliar low-fat and fruit and vegetable products leads to more positive taste expectations and stimulates choice for these products. The impact of level of food neophobia on such effects was studied. The present study had a two (taste information: yes/no) by four (food products: low-fat cheese/very low-fat margarine spread/fruit juice/fruit and vegetable juice) between subjects design among a convenience sample of 396 university students. Taste information was delivered by means of a poster providing information on the taste of the offered food product. Primary outcome measurements were taste expectations and product choice. Level of food neophobia, appetite level, mood states, usual intake of fruit, vegetables and fat, and demographics were taken into account as potential confounders. Taste information had no effect on taste expectations, although it had a positive effect on choosing unfamiliar healthful products. These effects were not moderated by level of food neophobia. Offering taste information on unfamiliar healthful products appears to be a promising strategy for increasing the first-time trial of such products, independent of the participants' level of food neophobia.