Trigeminal Sensation Research Articles

Astringency Is a Trigeminal Sensation That Involves the Activation of G Protein-Coupled Signaling by Phenolic Compounds

Astringency is an everyday sensory experience best described as a dry mouthfeel typically elicited by phenol-rich alimentary products like tea and wine. The neural correlates and cellular mechanisms of astringency perception are still not well understood. We explored taste and astringency perception in human subjects to study the contribution of the taste as well as of the trigeminal sensory system to astringency perception. Subjects with either a lesion or lidocaine anesthesia of the Chorda tympani taste nerve showed no impairment of astringency perception. Only anesthesia of both the lingual taste and trigeminal innervation by inferior alveolar nerve block led to a loss of astringency perception. In an in vitro model of trigeminal ganglion neurons of mice, we studied the cellular mechanisms of astringency perception. Primary mouse trigeminal ganglion neurons showed robust responses to 8 out of 19 monomeric phenolic astringent compounds and 8 polymeric red wine polyphenols in Ca(2+) imaging experiments. The activating substances shared one or several galloyl moieties, whereas substances lacking the moiety did not or only weakly stimulate responses. The responses depended on Ca(2+) influx and voltage-gated Ca(2+) channels, but not on transient receptor potential channels. Responses to the phenolic compound epigallocatechin gallate as well as to a polymeric red wine polyphenol were inhibited by the Gαs inactivator suramin, the adenylate cyclase inhibitor SQ, and the cyclic nucleotide-gated channel inhibitor l-cis-diltiazem and displayed sensitivity to blockers of Ca(2+)-activated Cl(-) channels.

Red hot: the crossmodal effect of color intensity on perceived piquancy.

Color cues can influence the experience of flavor, both by influencing identification and perceived intensity of foods. Previous research has largely focused on the crossmodal influence of vision upon taste or olfactory cues. It is plausible that color cues could also affect perceived trigeminal sensation; these studies demonstrate a crossmodal influence of color on piquancy. In our first two experiments, participants rated the spiciness of images of salsas that were adjusted to vary in color and intensity. We found that red was associated with significantly higher ratings of expected spice than blue, and that darker reds were expected to be spicier than lighter reds. In our third experiment, participants tasted and then rated the spiciness of each of four salsas (with two levels of color and of piquancy) when sighted and when blindfolded. Spiciness ratings were unaffected by differing colors when the salsa was mild, but when the piquancy was increased, a lack of increase in color corresponded to a depressed spiciness. These results can be explained using a model of assimilation and contrast. Taken together, our findings show that in our US sample, there is a crossmodal correspondence between visual and trigeminal senses that can influence perception of spiciness.

Trigeminal and Taste Sensations of the Tongue After Middle Ear Surgery

To establish clinical tests for measurement of trigeminal sensitivity on the human tongue and objectively assess changes in oral trigeminal sensitivity and taste ability after chorda tympani nerve (CTN) injury. Prospective study. University hospital. One-hundred and twenty-six patients with unilateral middle ear diseases who underwent primary middle ear surgery. Trigeminal sensation was measured each operated side as well as nonoperated side both before and 14 days after surgery using 3 kinds of tests: Semmes-Weinstein sensory test (SW test), 2-point discrimination test, and the electrostimulator test. Taste function was assessed with electrogustometry (EGM) similarly. The patients which the CTN was not touched (n = 6) showed no differences between preoperative and postoperative thresholds in any tests. In the patients with sectioned CTN (n=30), postoperative thresholds on the operated side were significantly higher than preoperative thresholds on the electrostimulator test, 2-point discrimination test, and EGM. In the patients with manipulated but not sectioned CTN (n = 90), postoperative thresholds were significantly higher than preoperative thresholds on the electrostimulator test and EGM. The patients with manipulated but not sectioned CTN and abnormal EGM postoperative thresholds (n = 48) showed that postoperative thresholds were significantly higher than preoperative thresholds in all tests. These findings suggest that the electrostimulator test was most useful to objectively assess small changes of trigeminal sensation among the 3 tests. The finding that trigeminal sensitivity of the tongue deteriorated on the operated side after CTN injury suggests that CTN function affected both taste sensation and trigeminal sensation of the tongue.

Swallowing kinematics and airway protection after palatal local anesthesia in infant pigs.

Abnormal kinematics during swallowing can result in aspiration, which may become life threatening. We tested the role of palatal sensation in the motor control of pharyngeal swallow in infants. In eight infant pigs, we reduced palatal sensation using local anesthesia (PLA) and measured the impact on swallowing kinematics and airway protection. The pigs drank milk containing barium while we simultaneously recorded videofluoroscopy and electromyography from fine wire bipolar electrodes in several hyolaryngeal muscles. We compared these results to control feedings and feedings following palatal saline injections. After PLA, four pigs had extreme jaw movements and abnormal tongue movement uncharacteristic of sucking. For this reason, we evaluated differences between these group B pigs and the others that could suck normally after PLA (group A). In the four group A pigs, after PLA there was less hyoid elevation (P < .001) but normal jaw and tongue movements. In group B, in addition to greater jaw movement (P < .001) there was more anterior and superior tongue movement (P < .001) and a larger range of hyoid movement (P < .001). The airway was protected in all of the pigs, indicating that these changes allowed successful adaptation to the reduction in palatal sensation. However, the oral and pharyngeal phases of the swallow were functionally linked, and trigeminal sensation influenced the motor control of the pharyngeal swallow. N/A.

Encoding and Representation of Intranasal CO2in the Mouse Olfactory Cortex

Intranasal trigeminal sensory input, often perceived as a burning, tingling, or stinging sensation, is well known to affect odor perception. While both anatomical and functional imaging data suggest that the influence of trigeminal stimuli on odor information processing may occur within the olfactory cortex, direct electrophysiological evidence for the encoding of trigeminal information at this level of processing is unavailable. Here, in agreement with human functional imaging studies, we found that 26% of neurons in the mouse piriform cortex (PCX) display modulation in firing to carbon dioxide (CO2), an odorless stimulant with known trigeminal capacity. Interestingly, CO2 was represented within the PCX by distinct temporal dynamics, differing from those evoked by odor. Experiments with ascending concentrations of isopentyl acetate, an odorant known to elicit both olfactory and trigeminal sensations, resulted in morphing of the temporal dynamics of stimulus-evoked responses. Whereas low concentrations of odorant evoked responses upon stimulus onset, high concentrations of odorant and/or CO2 often evoked responses structured to stimulus offset. These physiological experiments in mice suggest that PCX neurons possess the capacity to encode for stimulus modality (olfactory vs trigeminal) by differential patterns of firing. These data provide mechanistic insights into the influences of trigeminal information on odor processing and place constraints on models of olfactory-trigeminal sensory integration.

Memories Evoked by Odors Stimulating the Olfactory Nerve versus Odors Stimulating Both the Olfactory and Trigeminal Nerves: Possible Qualitative Differences?

The purpose of the study was to establish whether autobiographical memories differ when a stimulus producing olfactory or/and trigeminal sensations was used as memory cue. The following hypothesis was formulated: memories evoked by odors activating the trigeminal and olfactory nerves would be subjectively assessed as more detailed, more clear, more important and less happy, as compared to memories evoked by odors activating exclusively the olfactory nerve. The hypothesis was based on the assumption that trigeminal odors are perceived as signaling potential threats for the organism. 30 Polish psychology students (M age = 22 yr.; 20 women, 10 men) were tested using six odors: three stimulating the olfactory nerve only and three stimulating both the olfactory and trigeminal nerves. Participants were asked whether a particular odor evoked any memories, and if they answered "yes," they were to respond to four questions related to the qualities of the memory. Ratings of memories evoked by odors that stimulated the olfactory nerve and those that stimulated both the olfactory and trigeminal nerves differed in clarity. Odors stimulating the trigeminal nerve may induce less happy memories. The results are promising as to the role of the trigeminal system in coding and retrieval of survival-related memories.

The pungent substances piperine, capsaicin, 6-gingerol and polygodial inhibit the human two-pore domain potassium channels TASK-1, TASK-3 and TRESK

For a long time, the focus of trigeminal chemoperception has rested almost exclusively on TRP channels. However, two-pore domain (K2P) potassium channels have recently been identified as targets for substances associated with typical trigeminal sensations, such as numbing and tingling. In addition, they have been shown to be modulated by several TRP agonists. We investigated whether the pungent substances piperine, capsaicin, 6-gingerol and polygodial have an effect on human K2P channels. For this purpose, we evaluated the effects of these pungent substances on both wild-type and mutant K2P channels by means of two-electrode voltage-clamp experiments using Xenopus laevis oocytes. All four pungent substances were found to inhibit the basal activity of TASK-1 (K2P 3.1), TASK-3 (K2P 9.1), and TRESK (K2P 18.1) channels. This inhibitory effect was dose-dependent and, with the exception of polygodial on TASK-1, fully reversible. However, only piperine exhibited an IC50 similar to its reported EC50 on TRP channels. Finally, we observed for TASK-3 that mutating H98 to E markedly decreased the inhibition induced by piperine, capsaicin, and 6-gingerol, but not by polygodial. Our data contribute to the relatively sparse knowledge concerning the pharmacology of K2P channels and also raise the question of whether K2P channels could be involved in the pungency perception of piperine.

Sweet taste and chorda tympani transection alter capsaicin-induced lingual pain perception in adult human subjects

Sweetness signals the nutritional value of food and may moreover be accompanied by a sensory suppression that leads to higher pain tolerance. This effect is well documented in infant rats and humans. However, it is still debated whether sensory suppression is also present in adult humans. Thus, we investigated the effects of sweet taste on the perception of the painful trigeminal stimulus capsaicin in two groups of healthy adult human subjects. A solution of 100μM capsaicin was applied to the tip of the subject's tongues in order to stimulate trigeminal Aδ- and C-fiber nociceptors. When swallowed, 1M sucrose reduced the capsaicin-induced burning sensation by 29% (p≤0.05) whereas a solution of similar taste intensity containing 1μM quinine did not. Similarly, sucrose application to the frontal hemitongue suppressed the perception of the burning sensation induced by contralaterally applied capsaicin by 25% (p≤0.01). We furthermore investigated the effects of documented unilateral transection of the chorda tympani nerve on capsaicin perception. In accordance with the ipsi-to-contralateral effect of sucrose on capsaicin perception in healthy subjects, hemiageusic subjects were more sensitive for capsaicin on the tongue contralateral to the taste nerve lesion (+38%; p≤0.01). Taken together, these results argue I) for the existence of food intake-induced sensory suppression, if not analgesia, in adult humans and II) a centrally mediated suppression of trigeminal sensation by taste inputs that III) becomes disinhibited upon peripheral taste nerve lesion.

Individual Differences in the Chemical Senses: Is There a Common Sensitivity?

Taste, smell, and chemical irritation (so-called trigeminal sensation) combine in our daily experience to produce the supramodal sensation of flavor, are processed by partly overlapping neural mechanisms, and show functional interconnectivity in experiments. Given their collaboration in flavor formation and the well-established connections between these senses, it is plausible that polymodal detection mechanisms might contribute to individual differences in measured sensitivity. One would expect the existence of a general chemosensory sensitivity factor to result in associations among taste, smell, and trigeminal stimulation thresholds. Measures of 5 detection thresholds from all the chemical senses were assessed in the same group of young healthy subjects (n=57). An unbiased principal components analysis (PCA) yielded a 2-component solution. Component 1, on which taste thresholds loaded strongly, accounted for 29.4% of the total variance. Component 2, on which the odor and trigeminal lateralization thresholds loaded strongly, accounted for 26.9% of the total variance. A subsequent PCA restricted to a 3-component solution cleanly separated the 3 sensory modalities and accounted for 75% of the total variance. Thus, though there may be a common underlying factor that determines some individual differences in odor and trigeminal lateralization thresholds, a general chemical sensitivity that spans chemosensory modalities seems unlikely.

Perceiving Nasal Patency through Mucosal Cooling Rather than Air Temperature or Nasal Resistance

Adequate perception of nasal airflow (i.e., nasal patency) is an important consideration for patients with nasal sinus diseases. The perception of a lack of nasal patency becomes the primary symptom that drives these patients to seek medical treatment. However, clinical assessment of nasal patency remains a challenge because we lack objective measurements that correlate well with what patients perceive.The current study examined factors that may influence perceived patency, including air temperature, humidity, mucosal cooling, nasal resistance, and trigeminal sensitivity. Forty-four healthy subjects rated nasal patency while sampling air from three facial exposure boxes that were ventilated with untreated room air, cold air, and dry air, respectively. In all conditions, air temperature and relative humidity inside each box were recorded with sensors connected to a computer. Nasal resistance and minimum airway cross-sectional area (MCA) were measured using rhinomanometry and acoustic rhinometry, respectively. General trigeminal sensitivity was assessed through lateralization thresholds to butanol. No significant correlation was found between perceived patency and nasal resistance or MCA. In contrast, air temperature, humidity, and butanol threshold combined significantly contributed to the ratings of patency, with mucosal cooling (heat loss) being the most heavily weighted predictor. Air humidity significantly influences perceived patency, suggesting that mucosal cooling rather than air temperature alone provides the trigeminal sensation that results in perception of patency. The dynamic cooling between the airstream and the mucosal wall may be quantified experimentally or computationally and could potentially lead to a new clinical evaluation tool.

Arteriovenous malformation: a rare cause of trigeminal neuralgia identified by magnetic resonance imaging with constructive interference in steady state sequences

A 64-year-old female presented with a 4-year history of right-sided facial pain. She described an ‘electric shock-type’ pain starting on the right side of her chin that radiated along the lower lip, upper lip and into the lower cheek, in the mandibular division of the trigeminal nerve. The pain was triggered by speaking, eating, drinking, brushing her teeth or touching her chin. These attacks occurred daily and lasted for 3 months before resolving spontaneously, consistent with classical trigeminal neuralgia (TN). Systemic and neurological examinations were normal. In particular, trigeminal sensation was intact bilaterally and trigeminal reflexes were normal. A diagnosis of right-sided, mandibular division TN was made. She had four similar episodes of pain over the following 4 years, each lasting ∼3 months, with each episode becoming more severe. She did not want any analgesic medication for the first two episodes. However, during the most recent episode, carbamazepine (300 mg twice a day) and, subsequently, adjunctive amitriptyline (10 mg at night) were prescribed, although these failed to control the symptoms. Therefore the patient underwent investigation to assess for a structural cause amenable to neurosurgical intervention. The patient underwent a cranial MRI with constructive interference in steady state (CISS) sequences, which demonstrated several small blood vessels surrounding the right trigeminal nerve and a very large mass, thought likely to be a venous aneurysm, lying just behind the root entry zone into the trigeminal nerve (Figure 1). A contrast-enhanced computed tomography angiogram (CTA) confirmed the previous MRI findings and was highly suggestive of an underlying arteriovenous malformation (AVM) (Figure 2). For the pre-surgical work-up a digital subtraction angiogram was organized. This demonstrated a definite AVM during contrast injection in the right vertebral artery with rapid filling of the straight sinus during the early arterial phase (Figure …

SENSORY PROFILE DEVELOPMENT FOR AN ITALIAN PDO EWE'S MILK CHEESE AT TWO DIFFERENT RIPENING TIMES

ABSTRACT The sensory profile technique was applied to the Italian Protected Designation of Origin (PDO) Fiore Sardo cheese, made exclusively from raw ewe's milk in artisanal farms in Sardinia. The descriptive sensory analysis was used to find the sensory attributes which characterize this PDO cheese at two different ripening times (105 and 180 days). The product specification states that the cheese must have no less than 105 days of maturation before being sold, while at more than 180 days it is usually used grated. Twelve expert panelists, whose efficacy was confirmed by variance analysis, identified and evaluated 10 sensory attributes on cheese samples: smoked and rennet for odor; sour and salty for taste, piquant for trigeminal sensation; smoked and rennet for aroma; floury, grainy and friability for texture. The judges were also asked to provide an overall evaluation of sensory typicality. Cheeses from different farms ripened for 105 days differed significantly for smoked odor, salty, grainy and typicality, whereas the cheeses ripened for 180 days were significantly different for smoked odor, piquant, friability and sensory typicality. The comparison between cheeses from the same farm at 105 and 180 days showed no significant differences. PRACTICAL APPLICATIONSThe quality policy implemented in the European Union (EU) for agricultural products has met with growing interest among producers and consumers. Quality means to satisfy the expectations of the consumers. Indeed, consumers are giving increasing importance to the quality of foodstuffs rather than the quantity, generating a demand for agricultural products with an identifiable geographical origin. This can be obtained by providing certifications, such as Protected Designation of Origin and Protected Geographical Indication, with established characteristics of production and defined product characteristics, including sensory attributes which are strong determinants of acceptability. The study of traditional products, such as Fiore Sardo cheese, can be of considerable benefit to the rural economy (particularly in remote areas) by improving the incomes of farmers and by retaining the rural population in these areas. Moreover, the use of the sensory profile may help to preserve the identity of Fiore Sardo cheese by means of a sensory quality certification.

Investigation of interactions between texture and ortho- and retronasal olfactory stimuli using psychophysical and electrophysiological approaches

Flavor is a result of the complex combination of olfactory, gustatory and trigeminal sensations perceived during oral processing of foods, including thermal, painful, tactile and/or kinesthetic effects. Aim of this study was to better understand interactions between synchronous tactile (texture) and olfactory (odor) sensations, using a psychophysical and an electrophysiological approach. Texture stimuli were aliquots of lean milk and thickened lean milk. A butter aroma was presented either orthonasally or retronasally after oral processing and before swallowing the oral stimulus or in the absence of an oral stimulus. Eighteen subjects (11 women, 7 men, mean age 24 years), naïve to the expected effects, rated both odor and texture intensity of each stimulus. Event-related potentials (ERP) were obtained from five recording positions. For the psychophysical data, the presence of an oral stimulus increased odor intensity, irrespective of odor presentation route. For the electrophysiological data, both early and late chemosensory ERPs were affected by odor conditions, texture conditions, and their respective interaction. In conclusion: (1) perceptual interactions occurred between food texture and odor, with cross-modal interactions being found for both orthonasal and retronasal odor administration, and (2) these interactions between texture and odor occur at both primary-sensory and cognitive evaluative levels of stimulus processing. The temporal dimension plays then a critical role in the investigation of odor–texture interactions.

Relationship between oral burn and temperature in chili spiced pork patties evaluated by time–intensity

Time–intensity evaluation of chili spiced pork patties was performed to investigate the effect of chili concentration (0.25%, 0.5%, 1.0% and 2% w/w) and serving temperature (8, 38 and 67 °C) on oral burn. Increasing the chili concentration in the pork patties made the oral burn more intense and more persistent. Serving temperature of 38 °C and 67 °C gave more intense oral burn compared to when the pork patties were served at 8 °C, which could be caused by a temperature dependent binding of capsaicin to its receptor with optimum at oral cavity temperature. The effect of temperature on oral burn was however not dependent on capsaicin concentration. More studies on interactions between heat, gustatory, olfactory and trigeminal sensations can lead to a better understanding of how different food components interact, which would be useful in promoting culinary quality of food products and convenience meals.

Chemosensory effects during acute exposure to N-methyl-2-pyrrolidone (NMP)

Organic solvents are still essential in many industrial applications. To improve safety and health in the working environment lower occupational thresholds limits have been established and less toxic substitutes were introduced. N-Methyl-2-pyrrolidone (NMP) is a versatile solvent that is used as a substitute for dichloromethane in paint strippers. Due to conflicting results, there is a debate whether NMP causes irritations of the upper airways/eyes or not. In a human experimental study we examined the chemosensory effects of NMP under controlled conditions. Fifteen healthy males were investigated in a cross-over study. NMP vapor concentrations were 10, 40 and 80 mg/m 3 for 2 × 4 h with an exposure-free lunch break of 30 min. To maximize chemosensory effects a peak exposure scenario (25 mg/m 3 baseline, 160 mg/m 3 peaks 4 × 15 min, time-weighted average: 72 mg/m 3) was tested. The four different conditions were conducted with and without moderate physical workload. Chemosensory effects were measured physiologically by anterior rhinomanometry, eye blink rate and breathing frequency. Subjectively, ratings of acute health symptoms and intensity of olfactory and trigeminal sensations were collected repeatedly throughout the exposures. All physiological variables were unaffected by the different NMP concentrations and even the peak exposures were non-effective on these measures. Olfactory mediated health symptoms increased dose-dependently. For these symptoms a strong adaptation was observable, especially during the first 4 h of the exposures. Other acute symptoms were not significantly affected. Comparable to the symptoms, only olfactory sensations increased dose-dependently. Trigeminal sensations (e.g. eye and nose irritations) were evaluated as being barely detectable during the different exposures, only during 160 mg/m 3 exposure peak weak and transient eye irritation were reported. The results clearly suggest that NMP concentrations of up to 160 mg/m 3 caused no adverse sensory irritation or undue annoyance.

Chemosensory properties of murine nasal and cutaneous trigeminal neurons identified by viral tracing

BackgroundSomatosensation of the mammalian head is mainly mediated by the trigeminal nerve that provides innervation of diverse tissues like the face skin, the conjunctiva of the eyes, blood vessels and the mucouse membranes of the oral and nasal cavities. Trigeminal perception encompasses thermosensation, touch, and pain. Trigeminal chemosensation from the nasal epithelia mainly evokes stinging, burning, or pungent sensations. In vitro characterization of trigeminal primary sensory neurons derives largely from analysis of complete neuronal populations prepared from sensory ganglia. Thus, functional properties of primary trigeminal afferents depending on the area of innervation remain largely unclear.ResultsWe established a PrV based tracing technique to identify nasal and cutaneous trigeminal neurons in vitro. This approach allowed analysis and comparison of identified primary afferents by means of electrophysiological and imaging measurement techniques.Neurons were challenged with several agonists that were reported to exhibit specificity for known receptors, including TRP channels and purinergic receptors. In addition, TTX sensitivity of sodium currents and IB4 binding was investigated.Compared with cutaneous neurons, a larger fraction of nasal trigeminal neurons showed sensitivity for menthol and capsaicin. These findings pointed to TRPM8 and TRPV1 receptor protein expression largely in nasal neurons whereas for cutaneous neurons these receptors are present only in a smaller fraction. The majority of nasal neurons lacked P2X3 receptor-mediated currents but showed P2X2-mediated responses when stimulated with ATP. Interestingly, cutaneous neurons revealed largely TTX resistant sodium currents. A significantly higher fraction of nasal and cutaneous afferents showed IB4 binding when compared to randomly chosen trigeminal neurons.ConclusionIn conclusion, the usability of PrV mediated tracing of primary afferents was demonstrated. Using this technique it could be shown that compared with neurons innervating the skin nasal trigeminal neurons reveal pronounced chemosensitivity for TRPM8 and TRPV1 channel agonists and only partially meet properties typical for nociceptors. In contrast to P2X3 receptors, TRPM8 and TRPV1 receptors seem to be of pronounced physiological relevance for intranasal trigeminal sensation.

Intranasal trigeminal thresholds in healthy subjects

The trigeminal chemosensory system responds to irritation of the nasal cavity. Despite its dominant role as a sentinel in protecting the respiratory tract from harmful substances and its involvement in the perception of odorous substances, it has received relatively little attention compared to the olfactory system. Aim of the present study was the comparison of two psychophysical techniques to assess intranasal trigeminal thresholds, namely (A) responses of subjects who focused on intranasal trigeminally mediated sensations, and (B) the ability of subjects to identify the side of the nose receiving unilaterally presented stimuli. Method A (0.81 > r > 0.56) was found to show a higher test-retest reliability than Method B (0.48 > r > 0.40). Method A revealed thresholds that were approximately 32 times lower than those measured with method B. With method A women were found to have lower thresholds than men; no such difference could be detected between older and younger subjects. In conclusion, if the objective is to assess the level at which trigeminal sensations are detected with the utmost objectivity and unconfounded by smell, the obvious choice is B. If one's purpose is to assess the level at which trigeminal sensations are detected and the quality perceived, in the context of an odor one might opt for Method A. Thus, preference of one method over the other may depend on the question being asked, provided a well-instructed/trained panel of subjects is used.

Neural Correlates of Oral Irritation by Mustard Oil and other Pungent Chemicals: A Hot Topic

Together with taste and smell, oral sensations of touch, temperature, chemical irritation and pain play an important role in determining food flavor. Trigeminal sensations are mediated by sensory fibers innervating the oral mucosa that project via the lingual nerve to reach the brainstem trigeminal complex, with extensive terminations in subnucleus caudalis (Vc) (Carstens et al., 1995). Neurons in superficial laminae of dorsomedial Vc often respond to a wide range of thermal, mechanical and irritant chemical stimuli (Carstens et al., 1998). Different pungent chemicals elicit distinct temporal patterns of oral irritation. Repetitive application of capsaicin elicits a progressive rise in irritancy (sensitization; Green, 1989), as do piperine and concentrated salts and acids. In contrast, nicotine, menthol and cinnamaldehyde elicit irritation that declines across trials (desensitization; for a review, see Carstens et al., 2002). These contrasting patterns are also observed in the responses of Vc neurons (Dessirier et al., 2000) and may depend on the relative strength of opposing excitatory and desensitizing processes that are initiated in trigeminal nerve endings by a particular irritant. Recent molecular studies have uncovered the existence of six transient receptor potential (TRP) channels that account for thermal sensations from extreme cold to extreme heat (Jordt et al., 2003; Montell, 2003). Several of these also respond to irritant chemicals. Thus, TRPV1 (VR-1) is activated by noxious heat and capsaicin (Caterina et al., 1997), TRPM8 (CMR-1) by cooling and menthol (McKemy et al., 2002; Peier et al., 2002) and TRPA1 (ANKTM1) by intense cold, mustard oil, cinnamaldehyde, cannabinoids and other chemicals (Story et al., 2003; Bandell et al., 2004; Jordt et al., 2004). Our laboratory is particularly interested in the sensory properties of mustard oil in relation to TRPA1. In psychophysical experiments, lingual application of mustard oil (allyl isothiocyanate, 0.125%) elicited a desensitizing pattern of oral irritation and exhibited mutual cross-desensitization with capsaicin (Simons et al., 2003). Mustard oil similarly elicited a desensitizing firing pattern in Vc neurons recorded in anesthetized rats and crossdesensitized responses to pentanoic acid (Simons et al., 2004). However, mustard oil (1.25%) sensitized Vc responses to noxious heat, consistent with its well-known sensitizing effect on the skin. These contrasting effects of mustard oil (i.e. heat sensitization and chemical desensitization) are not consistent with peripheral or central sensitization, but might reflect a TRPA1-mediated enhancement of thermal gating of TRPV1 and an inhibition of chemical gating of TRPV1 (or other channels) co-expressed in the same trigeminal nerve endings. TRPA1 is activated by intense cold, mustard oil and cinnamaldehyde (Bandell et al., 2004) and we routinely record from Vc neurons that respond to these stimuli as well as to noxious heat and capsaicin (but not menthol). An example is shown in Figure 1. TRPA1 exhibits desensitization to repeated cooling (Story et al., 2003). We observed a significant decline in successive responses of Vc neurons to repeated lingual cooling (3°C) at rapid (15 s) intervals (Figure 2A,C). Vc responses usually also exhibited desensitization to repeated application of mustard oil or cinnamaldehyde (Figure 2B). Moreover, cold-evoked responses were significantly reduced following application of mustard oil or cinnamaldehyde (Figure 2B,D), suggesting a TRPA1 chemically mediated cross-desensitization of thermal gating of TRPA1. In conclusion, a substantial population of Vc neurons receives input from trigeminal afferents expressing TRPA1 and/or TRPV1, with some properties of TRPA1 being reflected in the responses of Vc neurons. It is curious that mustard oil, associated with a burning quality and intense cold, both apparently act via a common transduction mechanism. It is additionally puzzling as to how the nervous system can make qualitative discriminations based on input from neurons that respond to both noxious hot and cold stimuli. Nevertheless, the discovery of thermoand chemosensitive TRP channels has certainly spiced up the field of trigeminal chemoreception.

TASTE COMPONENTS OF CHEDDAR CHEESE: FRACTIONATION AND OPTIMIZATION OF CHEDDAR CHEESE TASTE IN WATER

ABSTRACT To determine the taste components of Cheddar cheese, we fractionated one mild Cheddar cheese and one aged Cheddar cheese by water extraction, freeze‐drying and gel filtration. Salty, sour and umami were the three predominant tastes present in the fractions. Neither trigeminal sensations nor astringency was perceived. We used response surface methodology to reconstruct a mild Cheddar cheese taste and an aged Cheddar cheese taste in water. Less salt and less acid were needed to simulate the taste of mild Cheddar cheese, compared with aged Cheddar cheese. Our optimized water solutions (containing sodium chloride, lactic acid and monosodium glutamate) were as similar to the real cheese samples as were the water extracts of the standard cheeses. However, neither our optimized solutions nor the water extracts matched the taste of the actual cheeses.

Development of a preliminary sensory lexicon for floral honey

The aim of this research was to develop a sensory vocabulary to describe floral honey from the south region of Spain (Andalucı́a). Principal component analysis has been used as a basis for excluding attributes that are not being used to differentiate among honeys or to describe the main sensory characteristics of each product. Fifteen descriptors were selected by PCA: four for odour (overall intensity, floral, ripen fruit, green grass and candy); three terms for texture (viscosity, gumminess and granularity); six for flavour (overall intensity, floral, ripen fruit, acid taste, bitter taste and sweet taste) and one attribute for trigeminal sensations (piquancy). The attributes are presented together with reference standards.