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PubMed2005

Delta-opioid receptor-immunoreactive neurons in the rat cranial sensory ganglia.

Immunohistochemistry for delta-opioid receptor (DOR) was performed on the rat cranial sensory ganglia. The immunoreactivity was detected in 16%, 19% and 11% of neurons in the trigeminal, jugular and petrosal ganglia, respectively. The nodose ganglion was devoid of such neurons. DOR-immunoreactive (IR) neurons were mostly small to medium-sized (trigeminal, range = 62-851 microm(2), mean +/- SD = 359 +/- 175 microm(2); jugular, range = 120-854 microm(2), mean +/- SD = 409 +/- 196 microm(2); petrosal, range = 167-1146 microm(2), mean +/- SD = 423 +/- 233 microm(2)). Double immunofluorescence method revealed that all DOR-IR neurons were also immunoreactive for calcitonin gene-related peptide. The cutaneous and mucosal epithelia in the oro-facial region, tooth pulp, taste bud and carotid body were innervated by DOR-IR nerve fibers. In the brainstem, IR nerve terminals were located in the superficial medullary dorsal horn and dorsomedial part of the subnucleus oralis as well as the solitary tract nucleus. The present study suggests that DOR-IR neurons may be associated with nociceptive and/or chemoreceptive function in the cranial sensory ganglia.

Animals↗
PubMed2006

Olfactory threshold increase in trigeminal neuralgia after balloon compression.

Idiopathic trigeminal neuralgia (ITN) is a well-known disease often treated with neurosurgical procedures, which may produce sensorial abnormalities, such as numbness, dysesthesia and taste complaints. We studied 12 patients that underwent this technique, in order to verify pain, gustative and olfactory thresholds abnormalities, with a follow-up of 120 days. We compared the patients with a matched control group of 12 patients. Our results found a significant difference in the olfactory threshold at the immediate post-operative period (p=0.048). We concluded that injured trigeminal fibers are probably associated with the increase in the olfactory threshold after the surgery, supporting the sensorial interaction theory.

Adult↗
PubMed2004

PROP taster status and self-perceived food adventurousness influence food preferences.

OBJECTIVE: To determine the influence of 6-n-propylthiouracil (PROP) taster status and food adventurousness on liking of bitter, hot, and pungent foods. DESIGN: Self-reported survey of food likes/dislikes for 70 foods. Subjects were classified as tasters or nontasters of PROP using a standard screening procedure. By their response to a query regarding their perceived frequency of trying unfamiliar foods, subjects were characterized as being more or less adventurous. SUBJECTS: A convenience sample of 232 healthy adults, 18 to 55 years of age, was recruited from the local community. Statistical analyses Individual foods were grouped using Principal Component Analysis. Analysis of variance was used to assess differences in liking of food groups as a function of PROP status and food adventurousness. RESULTS: PROP tasters who were more food adventurous liked chili peppers and hot sauce, other pungent condiments, strong alcohol, and bitter fruits and vegetables more than tasters who were less food adventurous (P< or =.05-.001). Nontasters liked most foods, and food adventurousness had little influence on food liking for these individuals. CONCLUSIONS: Food adventurous PROP tasters liked a wide variety of strong-tasting foods, whereas tasters who were less food adventurous showed the classic dislike of bitter, hot, and pungent foods. Previous studies might have overestimated the influence of PROP taster status on rejection of strong-tasting foods by not distinguishing individuals by food adventurousness.

Adolescent↗
PubMed2005

Neuronal cell death and population dynamics in the developing rat geniculate ganglion.

In contrast to many neuronal systems, the pattern of developmental neuronal degeneration in the rat geniculate ganglion has remained undefined. To address this issue sectioned geniculate ganglia from embryonic day 13 to postnatal day 3 have been examined using standard histological techniques, TdT-mediated dUTP-digoxigenin nick end labeling to verify apoptotic activity, bromo-deoxyuridine incorporation to monitor neuronal precursor proliferation, and anti-beta-neurotubulin III to verify the neuronal identity of pycnotic cells. Results summed from alternate (embryonic day 13) or every third (embryonic day 14-postnatal day 3) section show that neuronal degeneration occurs as early as embryonic day 13 (6.8% of neurons counted), well before geniculate innervation of lingual taste buds at embryonic day 16. A degenerative peak occurs at embryonic day 17 (9.5%) followed by a decline (1.7% at embryonic day 18) and leveling off (0.1%-0.2% at embryonic day 22-postnatal day 3). Thus, geniculate neuronal degenerative pattern includes both innervation-associated histogenetic and morphogenetic cell death. Corresponding counts of mean neuronal numbers in the sections showed a continual rise from embryonic day 13 through embryonic day 18 (approx. 330-760) followed by a slight decline at embryonic day 19 (to approx. 630) and then a final leveling off at 800-825 by embryonic day 20. This pattern differs from many other developing neural systems which show a major population crash during initial target contact. It likely reflects different but slightly overlapping neuronal precursor proliferation and degeneration patterns in multiple geniculate neuronal subpopulations.

Animals↗
PubMed2003

Lingual tactile acuity, taste perception, and the density and diameter of fungiform papillae in female subjects.

A growing body of evidence suggests that individuals who differ in taste perception differ in lingual tactile perception. To address this issue, spatial resolution acuity was estimated for 83 young adult females (52 Asians and 31 Caucasians) by their ability to examine with the tongue and identify embossed letters of the alphabet. Ratings of the magnitude of the bitterness of 0.0032M 6-n-propylthiouracil (PROP) were obtained to characterize subjects' taste perception. The density and diameter of fungiform papillae on the anterior tongues of the Asian subjects were measured also. Subjects who rated the bitterness of PROP as very or intensely strong (supertasters) were found to be about 25% more tactually acute than subjects who rated the bitterness as moderate to strong (medium tasters) and twice as acute as subjects who rated it as nondetectable or weak (non-tasters; P<.0001): The threshold heights for letter recognition averaged 2.8, 3.5 and 5.4 mm, respectively, for the Asian subjects and 2.6, 3.2, and 5.1 mm for the Caucasian subjects. The thresholds correlated highly with subjects' ratings of bitterness (rho=-0.84, P<.0001), and for the Asian subjects with the density (rho=-0.84, P<.0001) and diameter (rho=0.66, P<.0001) of fungiform papillae. Mean densities varied from 54.4 cm(-2) (non-tasters) to 106.5 cm(-2) (medium tasters) to 143.7 cm(-2) (supertasters; P<.0001). These findings confirm that individuals who differ in taste (PROP) sensitivity also differ in lingual tactile acuity. Tactile and taste sensitivities covary and reflect individual differences in the density and diameter of fungiform papillae on the anterior tongue.

Adolescent↗
PubMed2004

The distinctiveness of ionic and nonionic bitter stimuli.

The diverse chemical structures of stimuli that are bitter to humans suggest a need for multiple bitter receptors. Reactions of golden hamsters (Mesocricetus auratus) to 1 mM quinine hydrochloride, 3 mM denatonium benzoate, 180 mM magnesium sulfate, 30-100 mM caffeine, and 1-1.5 mM sucrose octaacetate (SOA) were studied to address whether there are multiple sensations elicited by bitter stimuli. Methods included behavioral generalization of LiCl-induced conditioned taste aversions (CTAs), intake preference tests, and electrophysiological recordings from the chorda tympani (CT) nerve. The five compounds, all bitter to humans, were all innately aversive to hamsters. CTA for the ionic quinine.HCl, denatonium benzoate, and MgSO(4) mutually cross-generalized and these ionic compounds were effective CT stimuli. Yet, the hamsters were much less sensitive to denatonium than humans, requiring a 100,000 times higher concentration for detection. CTA for nonionic caffeine and SOA did not cross-generalize to quinine or the other two ionic stimuli and these nonionic compounds were not effective CT stimuli. SOA and caffeine may elicit aversive reflexes or systemic reactions rather than taste sensations in the animals. Thus, the three ionic and two nonionic compounds form separate aversive stimulus classes in hamsters, neither of which appears to be a close homologue of the human bitter taste.

Animals↗
PubMed2004

Effects of stimulation duration on electrogustometric thresholds.

The ability to detect low electrical currents presented to the lingual surface is widely used to assess taste function in humans. Despite this fact, the influence of stimulus duration on electrical taste thresholds is not well established. In this study, we evaluated the effects of current duration (0.5, 1.0, and 1.5 s) on electrogustometric detection thresholds for two regions of the anterior tongue in 24 college students. Anodal stimulation was produced using a stainless steel 12.5-mm(2) electrode, and thresholds were determined using a single-staircase procedure. A non-monotonic function for the threshold values was observed for both tongue regions across the stimulus durations, with the 1.0-s duration stimulus resulting in a lower threshold value (i.e., higher sensitivity) than either the 0.5- or 1.5-s durations, which did not differ in magnitude from one another. These data suggest that stimulus-duration-related enhancement of lingual detection threshold sensitivity to electric currents disappears at some point after 1 s.

Adolescent↗
PubMed2006

Diverse tastes: Genetics of sweet and bitter perception.

Humans will eat almost anything, from caribou livers to rutabagas, but there are some types of foods, and their associated taste qualities, that are preferred by large groups of people regardless of culture or experience. When many choices are available, humans chose foods that taste good, that is, create pleasing sensations in the mouth. The concept of good taste for most people encompasses both flavor and texture of food, and these sensations merge with taste proper to form the concept of goodness. Although we acknowledge the universality of the goodness (sweet) or badness (bitter) of basic taste qualities, we also find that people differ, sometimes extremely so, in their ability to perceive and enjoy these qualities and, by extension, food and drink. The reasons for these differences among people are not clear but are probably due to a combination of experience beginning at an early age, perhaps in utero; learning, for example, as with conditioned taste aversions; sex and maturity; and perceptual differences that arise from genetic variation. In this review, we focus on individual variations that arise from genetic differences and review two domains of science: recent developments in the molecular biology of taste transduction, with a focus on the genes involved and second, studies that examine biological relatives to determine the heritability of taste perception. Because the receptors for sweet, savory (umami), and bitter have recently been discovered, we summarize what is known about their function by reviewing the effect of naturally occurring and man-made alleles of these receptors, their shape and function based on receptor modeling techniques, and how they differ across animal species that vary in their ability to taste certain qualities. We discuss this literature in the context of how taste genes may differ among people and give rise to individuated taste experience, and what is currently known about the genetic effects on taste perception in humans.

Animals↗
PubMed1985

Accession of sweet stimuli to receptors. I. Absolute dominance of one molecular species in binary mixtures.

Intensity/time studies of sweetness response in pure solutions of each of nine different sweet stimuli have been carried out. Both variables exhibit simple power functions of the form Intensity (S) = kscns and Persistence (P) = kpcnp. In binary mixtures of these nine stimuli a depression (or negative synergism) of both sweetness intensity and persistence is observed which is predictable from the low exponents of the power functions. Combination of both power functions allows the "effective concentration" of each stimulus in a binary mixture to be calculated from its observed intensity/time characteristics. All "effective concentrations" calculable in this way show absolute dominance of one stimulus in mixtures of two irrespective of the relative proportions of the two stimuli. It is suggested that the "effective concentrations" may reflect real concentrations of a single molecular species in the microenvironment of the receptor. Thus the accession of sweet molecules to ordered, localized concentrations at the receptor is ultimately dependent on chemical structure.

Adult↗
PubMed2001

Relationship of papillae number to bitter intensity of quinine and PROP within and between individuals.

Subjects were asked to assess the bitterness of one 6-n-propyl-2-thiouracil (PROP) and two quinine HCl (QHCl) concentrations presented via filter papers of varying sizes. The number of taste papillae stimulated by these filter papers was counted in each individual. Whole mouth sensitivity to PROP was determined in a separate session. In support of other demonstrations of spatial summation, these data indicated that perceived bitterness intensity increased as a function of area of stimulation within subjects. Between subjects, there was a significant trend for the perceived bitterness of PROP to increase with the lingual density of fungiform papillae, although this trend was highly variable and was only demonstrable among those who showed at least moderate sensitivity to PROP. On the other hand, the number of stimulated fungiform papillae failed to account for individual differences in perceived bitterness of QHCl.

Adult↗
PubMed2002

Electrogustometric thresholds: relationship to anterior tongue locus, area of stimulation, and number of fungiform papillae.

is well established that, on the anterior tongue, thresholds for chemical tastants are inversely related to the number of fungiform papillae. However, it is not known whether this is the case for thresholds to electrical currents presented to the lingual surface. In this study, electrical thresholds for 16 subjects were determined at four left-side anterior lingual locations: tongue tip (TT), a region 1.7 cm posterior to the tip, a region 3.4 cm posterior to the TT, and a region 1.7 cm from the tip along the lateral margin. Two electrode sizes were employed (12.5 and 50 mm2), and stimulus duration was held constant at 0.5 s. The number of fungiform papillae was determined using videomicroscopy. Analogous to what is seen with chemical stimulation, an inverse relationship was present between the mean electrical thresholds, expressed in terms of current density, and the number of papillae within the stimulated regions. The TT --which has the highest density of fungiform papillae -- was found to be more sensitive than the other tongue regions evaluated. Also paralleling chemical thresholds, the mean electrical threshold values were lower (i.e., sensitivity was higher) at a given tongue locus for the 50-mm2 than for the 12.5-mm2 stimulus area. Overall, this study demonstrates that thresholds for electrical stimulation vary across discrete regions of the anterior tongue and are specifically related to the number of fungiform papillae within the stimulated regions. These observations provide additional support for the hypothesis that lingual sensations induced by low levels of electrical current are mediated by the taste system.

Adolescent↗
PubMed1997

Cypha [propionic acid, 2-(4-methoxyphenol) salt] inhibits sweet taste in humans, but not in rats.

Cypha, propionic acid, 2-(4-methoxyphenol) salt, is a commercially available sweet taste inhibitor used in food products. The present study examined whether or not Cypha blocked the sweet taste response of rats. This was accomplished by measuring the consummatory response of rats to sucrose solutions during short-term taste tests. Nondeprived female rats were given 2-bottle choice tests (10 min) with different sucrose solutions. When given the choice between 10% sucrose and 10% sucrose containing Cypha at concentrations of 0.0125% to 0.10%, the rats showed no reliable preference for one or the other solution. In other tests, they reliably preferred 10% sucrose to 8%, 6%, and 4% sucrose, demonstrating the sensitivity of the behavioral test. To confirm the activity of the Cypha sample, a second experiment was conducted with human subjects. Using a visual analogue scale, the subjects rated the sweetness of various sucrose solutions (0% to 10%) and 10% sucrose solutions containing Cypha at concentrations of 0.0125% or 0.025%. Cypha reliably reduced the sweetness ratings of the sucrose solution. The 10% sucrose + 0.0125% Cypha solution was judged isosweet to 2.3-2.9% sucrose, and the 10% sucrose + 0.025% Cypha solution was rated as isosweet to a 1.2% sucrose solution. Taken together, these data confirm prior reports on the sweetness-inhibitory effect of Cypha in humans and demonstrate its ineffectiveness in rats. These findings are consistent with other reported differences between rats and humans in their response to other sweetness inhibitors, as well as to artificial sweeteners.

Adolescent↗
PubMed1997

Adaptation to capsaicin within and across days.

Subjects judged the time-course of the burn caused by 100 ppm capsaicin applied to the tongue on Day 1 and Day 5. On Days 2-4, they tasted hard candy containing capsaicin. Most subjects did not show adaptation within Day 1, but either plateaued after about 16 min or rose monotonically for the entire 34 min. Intensity was less on Day 5 and levelled off or declined for most subjects. Data were fit to a mathematical model of adaptation. Adaptation across days was accounted for by changes in the gains of the three processes.

Adaptation, Physiological↗
PubMed1998

Salt taste responses of the IXth nerve in Sprague-Dawley rats: lack of sensitivity to amiloride.

To explore characteristics of the salt taste function of taste receptor cells located on the posterior tongue, we recorded electrophysiological responses from the whole glossopharyngeal nerve in Sprague-Dawley (SD) rats. For all salts, relative response magnitudes increased with increased stimulus concentrations (0.2-2.0 M) of NH4+, K+, and Na+ salts. The order of effectiveness of stimulation for Cl- salts was NH4Cl > KCl > NaCl. For sodium salts, relative response magnitudes were anion dependent. Sodium salts with small anions (NaCl, NaSCN, and NaNO3) had a much stronger stimulating effect than sodium salts with large anion groups (Na2SO4, C2H3O2Na, and C6H11O7Na). The responses of the glossopharyngeal nerve to the Na+ salts of NaCl, C2H3O2Na, and C6H11O7Na were not inhibited by the lingual application of the epithelial sodium transport blocker amiloride. This is in contrast to large amiloride sensitivity of the chorda tympani nerve. Amiloride also failed to inhibit the responses to K+ salts (KCl and KC2H3O2) and to NH4Cl. These results demonstrate that taste receptors innervated by the glossopharyngeal nerve in SD rats lack amiloride sensitivity as observed in the glossopharyngeal nerve of spontaneously hypertensive and Wistar-Kyoto rats. Furthermore, the difference between the small-anion group and the large-anion group of Na+ salts in their effectiveness to produce responses in the glossopharyngeal nerve parallels the effects noted for the anion dependence in the portion of the taste response resistant to amiloride in the chorda tympani nerve. Sodium salts with the smaller anion produced the larger responses in both glossopharyngeal and chorda tympani nerves after amiloride.

Amiloride↗
PubMed2000

Taste effects of lingual application of cardiovascular medications.

Medications used to treat cardiovascular diseases such as congestive heart failure, high blood pressure, and arrhythmia, are prescribed extensively in Western countries. However, taste complaints are common side effects of many of these cardiovascular medications. Although clinical observations are helpful in determining potential taste problems from a medication, experimental studies are necessary to obtain quantitative data on taste. In the studies performed here, nine cardiovascular medications (labetalol HCl, captopril, diltiazem HCl, enalapril maleate, hydrochlorothiazide, propranolol HCl, mexiletine HCl, procainamide HCl, and propafenone HCl) were applied to the tongue in human volunteers to measure the direct effect of these drugs on taste receptors. The medications were applied topically to the tongue surface of both young and elderly subjects to mimic the situation in which the drug is secreted into the saliva. Detection thresholds ranged from 0.048 mM (propafenone) to 0.438 mM (procainamide). The detection thresholds of healthy elderly subjects did not significantly differ from young controls. The compounds tested had a predominantly bitter taste with other qualities as well. In addition, topical application of the medications to the tongue affected the taste of one or more taste stimuli, with medications differing in the pattern of taste effects exhibited. The mechanism of taste effects is not fully known, but the results of this study suggest one route may be due to medications' effect on peripheral taste receptors.

Administration, Sublingual↗