Taste and Smell Perception in Aging1

The taste and smell experience of other human beings cannot be known directly. Thus our understanding of age-related changes in the perception of taste and smell is derived inferentially. Inferences based on verbal reports and on the performance of tasks involving taste and smell stimuli suggest that some older individuals are impaired. The perceptual disadvantage of older adults appears to be more marked or more easily measured for complex than for simple stimuli. Some difference between older and younger adults may not be primarily sensory; others may arise from differences only incidentally associated with aging. The study of taste and smell perception in aging continues to challenge the psychophysical investigator to define the nature and extent of age-related change and to demonstrate its underlying mechanisms.     

Evaluating the 'Labeled Magnitude Scale' for Measuring Sensations of Taste and Smell

The Labeled Magnitude Scale (LMS) is a semantic scale of perceptualintensity characterized by a quasi-logarithmic spacing of itsverbal labels. The LMS had previously been shown to yield psychophysicalfunctions equivalent to magnitude estimation (ME) when gustatory,thermal and nociceptive stimuli were presented and rated together,and the upper bound of the LMS was defined as the ‘strongestimaginable oral sensation’. The present study comparedthe LMS to ME within the more limited contexts of taste andsmell. In Experiment 1, subjects used both methods to rate eithertaste intensity produced by sucrose and NaCl or odor intensityproduced by acetic acid and phenyl ethyl alcohol, with the upperbound of the LMS defined as either the ‘strongest imaginabletaste’ or the ‘strongest imaginable odor’.The LMS produced psychophysical functions equivalent to thoseproduced by ME. In Experiment 2 a new group of subjects usedboth methods to rate the intensity of three different tastequalities, with the upper bound of the LMS defined as the ‘strongestimaginable [sweetness, saltiness, or bitterness]’. Inall three cases the LMS produced steeper functions than didME. Experiment 3 tested the hypothesis that the LMS yields datacomparable to ME only when the perceptual domain under studyincludes painful sensations. This hypothesis was supported whenthe LMS again produced steeper functions than ME after subjectshad been explicitly instructed to omit painful sensations (e.g.the ‘burn’ of hot peppers) from the concept of ‘strongestimaginable taste’. We conclude that the LMS can be usedto scale sensations of taste and smell when they are broadlydefined, but that it should be modified for use in scaling specifictaste (and probably odor) qualities. The implications of theseresults for theoretical issues related to ME, category-ratioscales and the size of the perceptual range in different sensorymodalities are discussed. Chem. Senses 21: 323–334, 1996.     

Bitter Taste Receptor Polymorphisms and Human Aging

Several studies have shown that genetic factors account for 25% of the variation in human life span. On the basis of published molecular, genetic and epidemiological data, we hypothesized that genetic polymorphisms of taste receptors, which modulate food preferences but are also expressed in a number of organs and regulate food absorption processing and metabolism, could modulate the aging process. Using a tagging approach, we investigated the possible associations between longevity and the common genetic variation at the three bitter taste receptor gene clusters on chromosomes 5, 7 and 12 in a population of 941 individuals ranging in age from 20 to 106 years from the South of Italy. We found that one polymorphism, rs978739, situated 212 bp upstream of the TAS2R16 gene, shows a statistically significant association (p = 0.001) with longevity. In particular, the frequency of A/A homozygotes increases gradually from 35% in subjects aged 20 to 70 up to 55% in centenarians. These data provide suggestive evidence on the possible correlation between human longevity and taste genetics.     

Studies of Human Olfaction from the University of Pennsylvania Smell and Taste Center

This paper, presented in part as an invited lecture on the occasionof Professor E.P. Köster's retirement from Utrecht University,summarizes a large body of human studies performed at the Universityof Pennsylvania Smell and Taste Center during the last 17 years.Details of the development of standardized olfactory tests areprovided, including their validation and application in a widevariety of clinical and laboratory settings. Included are studiesrelated to transduction mechanisms in olfactory coding and factorsthat adversely influence olfactory function (e.g. age, gender,smoking, exposure to environmental chemicals, numerous diseases).A brief discussion of the strengths and weaknesses of the olfactoryvector hypothesis for neurodegenerative diseases is also presented.Chem. Senses 22: 565–586, 1997.     

味觉受体第一家族与味觉识别

哺乳动物味觉受体第一家族(taste receptor family 1 member,T1R)的发现提供了甜味与鲜味(氨基酸味)味觉识别与味觉概念一个重要的新视野。T1R包括T1R1、T1R2、T1R3三个成员。这些受体属于G蛋白偶联受体家族第3亚型,其中T1R2 T1R3以异二聚体形式共表达并参与甜味识别,而T1R1 T1R3也以异二聚体形式共表达并参与鲜味(氨基酸味)识别。对T1R的系列研究证明了味细胞对甜味和鲜味(氨基酸味)的选择性识别及其外周味觉编码的逻辑性。     

Taste Sensitivity and Aging: High Incidence of Decline Revealed by Repeated Threshold Measures

Contrary to what has often been said about the subject, declinein taste sensitivity with aging characterizes virtually everybodyand is not the artificial result of averaging large losses ofa minority with negligible losses of a majority. This assertionis supported by six repeated measures of sucrose thresholdsin each of 15 older (over 64 years) and 15 younger (under 27years) adult subjects. Threshold was determined by a proceduresimilar to past studies and with the same results: much scatterand considerable overlap between the thresholds of younger andolder subjects. A quite contrasting picture emerges, however,when each subject's six threshold determinations are averaged.Averaging shrinks the individual differences among subjects,as well as the over-lap between younger and older subjects.Although virtually all elderly subjects now revealed taste weakness,reliable individual differences in degree of weakness aboundamong them, suggesting various individual rates of physiologicalaging. In contrast young persons exhibit greater uniformityof sensitivity. These findings were brought out by inter-testcorrelations, which were much higher for the older subjects;i.e. an older subject who tended to score high (low) on onetest tended to score high (low) on the other tests. The studyconfirms the tenuous nature of brief threshold tests as indicesof personal sensitivity as found earlier also in olfactory thresholdsand in concurrent measurement of two-point touch thresholdsin the present study. This revealed correlated losses betweenrepeated taste and touch thresholds from the same 15 older subjects,unrelated to their exact chronological age. Chem. Senses 20:451–459, 1995.     

The Effects of Aging on Conflict Detection

Several cognitive changes characterize normal aging; one change regards inhibitory processing and includes both conflict monitoring and response suppression. We attempted to segregate these two aspects within a Go/No-go task, investigating three age categories. Accuracy, response times and event-related potentials (ERPs) were recorded. The ERP data were analyzed, and the Go and No-go trials were separated; in addition, the trials were organized in repeat trials (in which the subjects repeated the action delivered in the previous trial) and switch trials (in which the subjects produced a response opposite to the previous response). We assumed that the switch trials conveyed more conflict than the repeat trials. In general, the behavioral data and slower P3 latencies confirmed the well-known age-related speed/accuracy trade-off. The novel analyses of the repeat vs. switch trials indicated that the age-related P3 slowing was significant only for the high conflict condition; the switch-P3 amplitude increased only in the two older groups. The ‘aging switch effect’ on the P3 component suggests a failure in the conflict conditions and likely contributes to a generalized dysfunction. The absence of either a switch effect in the young group and the P3 slowing in middle-aged group indicate that switching was not particularly demanding for these participants. The N2 component was less sensitive to the repeat/switch manipulation; however, the subtractive waves also enhanced the age effects in this earlier time window. The topographic maps showed other notable age effects: the frontal No-go N2 was nearly undetectable in the elderly; in the identical time window, a large activity in the posterior and prefrontal scalp regions was observed. Moreover, the prefrontal activity showed a negative correlation with false alarms. These results suggest that the frontal involvement during action suppression becomes progressively dysfunctional with aging, and additional activity was required to reach a good level of accuracy.     

Effects of Flooding and Drought on the Anatomy of Paspalum dilatatum

Paspalum dilatatum occupies different topographic positionsin the Flooding Pampa, Argentina. Populations from differentpositions are subjected to various regimes of flooding and drought,both of which may occur in the same growing season. We investigatedthe constitutive and plastic anatomical traits of P. dilatatumpopulations from habitats with contrasting regimes of floodingand drought. Both events affected root and sheath anatomy, andthese effects were similar for clones from different topographicpositions. Flooding increased the aerenchymatous tissue in theroot cortex and the leaf sheaths and decreased the number ofroot hairs per unit of root length. Drought decreased the diameterof root metaxylem vessels, thus lowering the risk of embolismsand increasing water-flow resistance, and increased the numberof root hairs, thereby increasing water uptake ability. In additionto these plastic responses, all clones showed constitutive characteristicsthat may confer an ability to withstand sudden events of floodingor drought: a high proportion of aerenchyma, which may maintainaeration before plastic responses take place; sclerenchyma,which may prevent root and leaf sheath collapse by soil compaction;and a conspicuous endodermis, which may protect stelar tissuesfrom desiccation. Both constitutive and plastic anatomical characteristicsare likely to contribute to the ability of this species to occupywidely different topographic positions and to resist temporalvariations in water and oxygen availability. Copyright 2001Annals of Botany Company Flooding, drought, aerenchyma, vessels, roots, leaf sheaths, anatomy, Paspalum dilatatum Poir     

Synergistic Taste Effects of Some New Ribonucleotide Derivatives

Taste effects of six newly synthesized ribonucleotide derivatives, i.e., disodium salts of 2-methyl-5′-inosinic acid · 6H₂O, 2-ethyl-5′-inosinic acid · 1.5H₂O, 2-N-methyl-5′-guanylic acid · 5.5H₂O, 2-N-dimethyl-5′-guanylic acid · 2.5H₂O, 2-methylthio-5′-inosinic acid · 6H₂O and 2-ethylthio-5′-inosinic acid · 2H₂O, were studied. Stimulus thresholds (detection thresholds) of these derivatives ranged from about 0.02 to 0.006 g/100ml. Flavor-enhancing activities of them were 2.3 to 8.0 times larger than that of disodium 5′-inosinate · 7.5H₂O IMP) in the synergistic effect with monosodium glutamate. Furthermore, the quality of taste of all the derivatives was recognized to be the same kind to that of IMP.     

A Study of the Effects of Aging on Parathormone Induced Osteoclastogenesis in the Mouse1

The effects of aging on the ability of parathormone (PTH) to induce osteoclastogenesis in the femora of mice was investigated. Seventy BNL short-lived mice ranging in age from 5 to 104 weeks were used and divided in 5 age groups. Fifty-two mice were Injected i.p. with 5U/gm body weight and sacrificed every 6 hours for 24 hours. Both femora were fixed, decalcified and routinely prepared histologically. All osteoclasts observed at the distal metaphyseal region were microscopically counted, as well as their nuclei. Cell size was also measured. The results showed that the ability of PTH to induce osteoclastogenesis is not lost with age, but is significantly reduced. Furthermore, the tissue response is prolonged with age from 12 to 24 hours. The earlier reports in the literature that osteoclasts originate from fusion of osteogenic cell precursors was supported by the present study. This does not eliminate the fact that alternative origins may also be possible. Observed morphological differences in osteoclasts are most probably functionally related, with loss of function due to aging not being ruled out.     

The Effects of Aging on Researchers' Publication and Citation Patterns

The average age at which U.S. researchers receive their first grant from NIH has increased from 34.3 in 1970, to 41.7 in 2004. These data raise the crucial question of the effects of aging on the scientific productivity and impact of researchers. Drawing on a sizeable sample of 6,388 university professors in Quebec who have published at least one paper between 2000 and 2007, our results identify two turning points in the professors'' careers. A first turning point is visible at age 40 years, where researchers start to rely on older literature and where their productivity increases at a slower pace—after having increased sharply since the beginning of their career. A second turning point can be seen around age 50, when researchers are the most productive whereas their average scientific impact is at its lowest. Our results also show that older professors publish fewer first-authored papers and move closer to the end of the list of co-authors. Although average scientific impact per paper decreases linearly until about age 50, the average number of papers in highly cited journals and among highly cited papers rises continuously until retirement. Our results show clearly that productivity and impact are not a simple and declining function of age and that we must take into account the collaborative aspects of scientific research. Science is a collective endeavor and, as our data shows, researchers of all ages play a significant role in its dynamic.