Receptor sites for amino acids in the facial taste system of the channel catfish

1. Receptor sites for different amino acids in the facial taste system of the channel catfish, Ictalurus punctatus, were determined from in vivo electrophysiological cross-adaptation experiments. 2. Relatively independent receptor sites were indicated for L-proline, D-proline, D-arginine, L-histidine and L-lysine, as well as those previously reported for L-alanine, L-arginine and D-alanine. 3. The functional isolation of two nerve twigs that were more responsive to D-alanine than to L-alanine or to other test stimuli provided further evidence for the existence of D-alanine sites that are independent from those to L-alanine. 4. Under all cross-adaptation regimes, the taste responses to the majority of test stimuli were reduced. Various possible mechanisms accounting for this generalized reduction in action potential activity during adaptation are discussed.     

严重缺碘对体质及遗传性状影响的研究

对严重缺碘地区一个容貌特殊,身材较矮,智力低下的人群进行了体质特征及遗传性状的研究,并与国内有关本地区的调查资料进行了对照,提出人类体质特征和遗传性状除与人种、地理环境异同直接相关外,人体不可缺少的微量元素的摄入水平在一定程度上对其也产生影响。并且认为同一人种、民族居住同一地理位置所产生的体质差异应从水文、地质、生活方式、生活水平的不同进行综合分析。     

The effect of age on the recognition thresholds of three sweeteners: sucrose,saccharin and aspartame

It iS believed that people's sensitivity to taste declines with age but the evidence is inconclusive. This study was designed to test the hypothesis that taste recognition thresholds (TRTs) for sweetness are higher in older than in younger individuals, using groups of 16 younger subjects (18–30) and 16 older subjects (60–85). Three test substances were used: sucrose, aspartame and saccharin. A questionnaire recorded variables which might have affected TRTs, but data failed to show any trend that might have biased the principle variate-age. There was a significant alteration with age of recognition thresholds, at least for sucrose and saccharin. The differences between the groups for the three sweeteners were due to the fact that all the very sensitive subjects were young. None of the older subjects had particularly poor discrimination: all but one had TRTs within the range of younger subjects. Although there are age-related taste changes, they are much less dramatic than commonly occurs with other senses, such as sight and hearing. The findings of this study have implications for institutional catering and the dietary management of older people using non-sugar sweeteners.     

革胡子鲇上颌须离体标本味觉反应的测定

本实验采用革胡子鲇离体上颌须－传入神经标本,记录传入神经电活动,测定了须部味蕾对动物组织浸提液、氨基酸、酸盐化合物等多种化学刺激的反应。发现某些物质有较强的刺激作用。另外,机械刺激也引起较强的反应。分析传入神经单纤维的记录结果,可将化学刺激引起的味觉反应分为３种单元类型：（１）对精氨酸特别敏感;（２）对柠檬酸和氯化胺有较强的反应;（３）对多种刺激都有一定的反应。实验表明,革胡子鲇的须部味蕾可能是一     

Isolation of taste buds from the foliate papillae of the rabbit

Summary A method to isolate taste buds from the foliate papillae of the rabbit tongue is described. The method comprises (a) separation of the epidermis from the dermal layer after treatment with dilute acetic acid, and (b) mechanical removal of the taste buds from the epithelium with the use of a surgical needle. The procedure yields taste buds that are morphologically well preserved, and in quantities sufficient to enable a detailed biochemical characterization. Preliminary tests have shown the taste buds to have biochemical properties clearly distinct from those of the adjacent epithelium. The method may provide a basis for studying the molecular mechanism of taste perception in greater detail.On leave of absence from the Medical Research Centre, Polish Academy of Sciences, Warsaw, Poland.     

Freeze-fracture study of taste bud pores in the foliate papillae of the rabbit

Summary In freeze-fractured specimens of taste buds from the foliate papillae of rabbits, the intercellular spaces are separated from the pore of the taste bud by zonulae occludentes of the tight-type. Below these tight junctions numerous desmosomes are found at irregular intervals. The epithelial cells adjacent to the pore are also joined by single strands of fusion. The microvilli arising from the neck of the type I cells have a high particle density. The microvilli of type II cells and especially the short microvilli of peripherally situated cells have a lower intramembranous particle density. The single microvillus of type III cells has a very large diameter and is longer than the other microvilli. It contains a few larger intramembranous particles and vesicle-like protrusions of the membrane facing the cytoplasm. Transverse fracturing reveals a filamentous fine structure in all microvilli. The physiological implications of these observations are discussed.Supported by grants from the Deutsche Forschungsgemeinschaft (Ja 205/5+6)     

Ago-Allosteric Modulation and Other Types of Allostery in Dimeric 7TM Receptors

Conventionally, an allosteric modulator is neutral in respect of efficacy and binds to a receptor site distant from the orthosteric site of the endogenous agonist. However, recently compounds being ago-allosteric modulators have been described i.e., compounds acting both as agonists on their own and as enhancers for the endogenous agonists in both increasing agonist potency and providing additive efficacy—superagonism. The additive efficacy can also be observed with agonists, which are neutral or even negative modulators of the potency of the endogenous ligand. Based on the prevailing dimeric concept for 7TM receptors, it is proposed that the ago-allosteric modulators bind in the orthosteric binding site, but–importantly–in the “other” or allosteric protomer of the dimer. Hereby, they can act both as additive co-agonists, and through intermolecular cooperative effects between the protomers, they may influence the potency of the endogenous agonist. It is of interest that at least some endogenous agonists can only occupy one protomer of a dimeric 7TM receptor complex at a time and thereby they leave the orthosteric binding site in the allosteric protomer free, potentially for binding of exogenous, allosteric modulators. If the allosteric modulator is an agonist, it is an ago-allosteric modulator; if it is neutral, it is a classical enhancer. Molecular mapping in hetero-dimeric class-C receptors, where the endogenous agonist clearly binds only in one protomer, supports the notion that allosteric modulators can act through binding in the “other” protomer. It is suggested that for the in vivo, clinical setting a positive ago-allosteric modulator should be the preferred agonist drug.     

A fly rhodopsin sheds light on thermal taste

In their recent paper, Li and colleagues discover that cold food tastes less sweet to flies, in part by activating bitter sensory neurons through a rhodopsin-dependent mechanism [1]. This work establishes temperature as an important variable in understanding fly taste processing and adds diversity to the sensory roles for rhodopsin receptors.     

Multiple Shh signaling centers participate in fungiform papilla and taste bud formation and maintenance

The adult fungiform taste papilla is a complex of specialized cell types residing in the stratified squamous tongue epithelium. This unique sensory organ includes taste buds, papilla epithelium and lateral walls that extend into underlying connective tissue to surround a core of lamina propria cells. Fungiform papillae must contain long-lived, sustaining or stem cells and short-lived, maintaining or transit amplifying cells that support the papilla and specialized taste buds. Shh signaling has established roles in supporting fungiform induction, development and patterning. However, for a full understanding of how Shh transduced signals act in tongue, papilla and taste bud formation and maintenance, it is necessary to know where and when the Shh ligand and pathway components are positioned. We used immunostaining, in situ hybridization and mouse reporter strains for Shh, Ptch1, Gli1 and Gli2-expression and proliferation markers to identify cells that participate in hedgehog signaling. Whereas there is a progressive restriction in location of Shh ligand-expressing cells, from placode and apical papilla cells to taste bud cells only, a surrounding population of Ptch1 and Gli1 responding cells is maintained in signaling centers throughout papilla and taste bud development and differentiation. The Shh signaling targets are in regions of active cell proliferation. Using genetic-inducible lineage tracing for Gli1-expression, we found that Shh-responding cells contribute not only to maintenance of filiform and fungiform papillae, but also to taste buds. A requirement for normal Shh signaling in fungiform papilla, taste bud and filiform papilla maintenance was shown by Gli2 constitutive activation. We identified proliferation niches where Shh signaling is active and suggest that epithelial and mesenchymal compartments harbor potential stem and/or progenitor cell zones. In all, we report a set of hedgehog signaling centers that regulate development and maintenance of taste organs, the fungiform papilla and taste bud, and surrounding lingual cells. Shh signaling has roles in forming and maintaining fungiform papillae and taste buds, most likely via stage-specific autocrine and/or paracrine mechanisms, and by engaging epithelial/mesenchymal interactions.