Chemical senses and aging: taste versus smell

Earlier studies have suggested that aging may adversely affectthe sense of smell more than the sense of taste. Although bothsense modalities lose some absolute (threshold) sensitivity,agerelated losses of suprathreshold magnitude seem to occurcommonly in the sense of smell, less commonly in the sense oftaste. This apparent difference between taste and smell wasput to direct test in the same subjects in the same test session.Young (20–25 years) and two groups of elderly people (65–78and 80–95 years) estimated the taste intensity of variousconcentrations of NaCl and the odor intensity of various levelsof iso-amyl butyrate, under instruction to make magnitude estimationsof both kinds of stimuli on a common scale. Relative to thetaste estimates, the old gave lower odor estimates than theyoung. Also, the 80–95 year group showed, on average,a greater odor deficit than the 65–78 year group. Thisoutcome supports the main hypothesis that as age increases smelldeficits present a more serious problem than do taste deficits.     

Olfaction and taste senses in sturgeon behaviour

Olfaction is one of the fundamental senses for spawning and feeding behaviour in sturgeons. The olfactory spectra of free amino acids affecting behaviour in sturgeon species of the family Acipenseridae are narrow and similar. The threshold concentrations for effective amino acids (glycine and L-alanine) are 1 μM The taste spectra are highly species specific, especially for the oral taste modality. There is a good correlation between the responses of extra-oral and oral taste systems within the same species. The extra-oral taste system is more sensitive and has a wider effective spectrum than the oral system. The extra-oral taste system develops more rapidly than oral taste system during sturgeon ontogenesis.     

Effects of expression of mammalian G alpha and hybrid mammalian-yeast G alpha proteins on the yeast pheromone response signal transduction pathway.

Scg1, the product of the Saccharomyces cerevisiae SCG1 (also called GPA1) gene, is homologous to the alpha subunits of G proteins involved in signal transduction in mammalian cells. Scg1 negatively controls the pheromone response pathway in haploid cells. Either pheromonal activation or an scg1 null mutation relieves the negative control and leads to an arrest of cell growth in the G1 phase of the cell cycle. Expression of rat G alpha s was previously shown to complement the growth defect of scg1 null mutants while not allowing mating. We have extended this analysis to examine the effects of the short form of G alpha s (which lacks 15 amino acids present in the long form), G alpha i2, G alpha o, and Scg1-mammalian G alpha hybrids. In addition, we have found that constructs able to complement scg1 are also able to inhibit the response to pheromone and mating when expressed in a wild-type SCG1 strain. Overexpression of Scg1 has a similar inhibitory effect. These results are consistent with a model proposed for the action of Scg1 as the alpha component of a heterotrimeric G protein in which the beta gamma component (Ste4/Ste18) activates the pheromone response after dissociation from Scg1. They suggest that the G alpha constructs able to complement scg1 can interact with beta gamma to prevent activation of the pathway but are unable to interact with pheromone receptors to activate the pathway.     

Magnitude-matching: the measurement of taste and smell

In the method of magnitude-matching, subjects try to judge intensitiesof sensations from two or more modalities on a single, commonscale. Using responses to one modality as a standard makes itpossible to compare subjects' suprathreshold perceptions onthe other, test modality. A series of ten experiments revealedthe following: (i) magnitude-matching ‘works’: withboth loudness of tones and lightness of grays as standards,tasters versus nontasters of 6-n-prophylthiouracil (PROP) (asdefined by a threshold criterion) show much greater responceto suprathreshold PROP and slightly greater response to surcose;(ii) though superior to rating-scale judgements of sensory intensitymade without reference to a second modality, magnitude-matchingis not, however, flawless: the cross-modality matching relationproduced by a set of magnitude-matches depends systematicallyon the contextual sets of stimulus levels presented for judgement;(iii) with taste as the standard, old versus young subjectsshowed only a 25% decrement in responce to the odor intensityof butanol when both groups recieved the same physical (concentration)levels, but a >50% decrement in responce when both groupsrecieved about the same perceptual levels; (iv) magnitude-matchesare much the same whether subjets make their judgements on abounded rating-scale or an open-ended magnitude-estimation scale:and (v) loudness, lightness and odor intensity serve about equallyin magnitude-matching with taste intensity.     

FET-based nanobiosensors for the detection of smell and taste

Various nanobiosensors composed of biomaterials and nanomaterials have been developed, due to their demonstrated advantage of showing high performance. Among various biomaterials for biological recognition elements of the nanobiosensor, sensory receptors, such as olfactory and taste receptors, are promising biomaterials for developing nanobiosensors, because of their high selectivity to target molecules. Field-effect transistors(FET) with nanomaterials such as carbon nanotube(CNT), graphene, and conducting polymer nanotube(CPNT), can be combined with the biomaterials to enhance the sensitivity of nanobiosensors.Recently, many efforts have been made to develop nanobiosensors using biomaterials, such as olfactory receptors and taste receptors for detecting various smells and tastes. This review focuses on the biomaterials and nanomaterials used in nanobiosensor systems and studies of various types of nanobiosensor platforms that utilize olfactory receptors and taste receptors which could be applied to a wide range of industrial fields, including the food and beverage industry, environmental monitoring, the biomedical field, and anti-terrorism.     

Purification and characterization of subforms of the guanine-nucleotide-binding proteins G alpha i and G alpha o

Five different pertussis-toxin-sensitive guanine-nucleotide-binding proteins (G proteins) were purified from bovine brain. Immunochemical characterization of alpha subunits identified two G alpha o proteins (G alpha o-I and G alpha o-II), two 41-kDa G alpha i proteins (G alpha i-I and G alpha i-II) and the 40-kDa G alpha i2 protein. Site-directed antisera specific for G alpha o proteins did not differentiate between G alpha o-I and G alpha o-II. However, in situ peptide mapping using polyacrylamide gel electrophoresis revealed distinct cleavage products with different proteases for each of these proteins. Additionally comparison of Rf values demonstrated a slightly faster migration for G alpha o-II than for G alpha o-I, which is the only type of G alpha o protein present in cell membranes of the neuroblastoma/glioma cell line NG 108-15. The importance of these structural differences and possible functional implications are discussed.     

Structural correlates of taste and smell loss in encephalitis disseminata

Background

Olfactory dysfunction in MS patients is reported in the literature. MRI of the olfactory bulb (OB) is discussed as a promising new testing method for measuring olfactory function (OF).Aim of this study was to explore reasons for and optimize the detection of olfactory dysfunction in MS patients with MRI.

Materials and Methods

OB and olfactory brain volume was assessed within 34 MS patients by manual segmentation. Olfactory function was tested using the Threshold-Discrimination-Identification-Test (TDI), gustatory function was tested using Taste Strips (TST).

Results

41% of the MS patients displayed olfactory dysfunction (8% of the control group), 16% displayed gustatory dysfunction (5% of the control group). There was a correlation between the OB volume and the number and volume of MS lesions in the olfactory brain. Olfactory brain volume correlated with the volume of lesions in the olfactory brain and the EDSS score. The TST score correlated with the number and volume of lesions in the olfactory brain.

Conclusion

The correlation between a higher number and volume of MS lesions with a decreased OB and olfactory brain volume could help to explain olfactory dysfunction.     

Homologous and unique G protein alpha subunits in the nematode Caenorhabditis elegans.

A cDNA corresponding to a known G protein alpha subunit, the alpha subunit of Go (Go alpha), was isolated and sequenced. The predicted amino acid sequence of C. elegans Go alpha is 80-87% identical to other Go alpha sequences. An mRNA that hybridizes to the C. elegans Go alpha cDNA can be detected on Northern blots. A C. elegans protein that crossreacts with antibovine Go alpha antibody can be detected on immunoblots. A cosmid clone containing the C. elegans Go alpha gene (goa-1) was isolated and mapped to chromosome I. The genomic fragments of three other C. elegans G protein alpha subunit genes (gpa-1, gpa-2, and gpa-3) have been isolated using the polymerase chain reaction. The corresponding cosmid clones were isolated and mapped to disperse locations on chromosome V. The sequences of two of the genes, gpa-1 and gpa-3, were determined. The predicted amino acid sequences of gpa-1 and gpa-3 are only 48% identical to each other. Therefore, they are likely to have distinct functions. In addition they are not homologous enough to G protein alpha subunits in other organisms to be classified. Thus C. elegans has G proteins that are identifiable homologues of mammalian G proteins as well as G proteins that appear to be unique to C. elegans. Study of identifiable G proteins in C. elegans may result in a further understanding of their function in other organisms, whereas study of the novel G proteins may provide an understanding of unique aspects of nematode physiology.     

Purification of unique alpha subunits of GTP-binding regulatory proteins (G proteins) by affinity chromatography with immobilized beta gamma subunits

Novel G protein alpha subunits were purified from rat brain by an affinity matrix containing immobilized beta gamma subunits (Pang, I.-H., and Sternweis, P. C. (1989) Proc. Natl. Acad. Sci. U. S. A. 86, 7814-7818). They were unique based on the following criteria. These alpha subunits migrated differently through polyacrylamide gels with an apparent molecular mass of 42 kDa. They did not behave similarly to the other brain G proteins by conventional chromatographic techniques. Antisera raised against a common region of known alpha subunits failed to recognize these 42-kDa polypeptides. Finally, primary sequences of tryptic fragments of these proteins contain regions homologous to, yet unique from, the other alpha subunits. Sequences are identical with one or more members of a new family of alpha subunits recently identified by molecular genetic techniques (Strathmann, M., Wilke, T. M., and Simon, M. I. (1989) Proc. Natl. Acad. Sci. U. S. A. 86, 7407-7409); most of the primary sequence identifies an alpha subunit labeled alpha q. These polypeptides were not substrates for ADP-ribosylation catalyzed by pertussis toxin. They bound GTP gamma S only with slow rates and low stoichiometry. Antisera to peptides based on primary sequence were specific for the new alpha subunits and indicate that they are widely distributed at low levels in different tissues but more concentrated in brain and lung. This procedure provides a means of preparing native G proteins that have a potential role as modulators of pertussis toxin-insensitive regulatory pathways.     

Temporal synchrony and integration of sub-threshold taste and smell signals

The importance of stimulus timing and location on the perceptual integration of taste and odour was studied based on a sub-threshold methodology. From a panel of 16 people, 12 showed the integration effect previously reported while 4 showed no effect. The experiment was repeated using retronasal and orthonasal delivery of the odour and with tastant present or absent in the mouth. Integration of taste and odour only occurred when both stimuli were present at the same time. Retro- or orthonasal presentation both produced integration providing that tastant delivery was synchronous but the threshold values for the two presentation methods were different. The relevance of these findings to flavour perception under realistic conditions is considered.     

Two G12 family G proteins, G alpha12 and G alpha13, show different subcellular localization

The G alpha subunits of the G12 family of heterotrimeric G proteins, G alpha12 and G alpha13, are closely related in sequences and some effectors, but they often act through different pathways or bind to different proteins. We have examined subcellular distribution of these two G proteins and found that endogenous G alpha12 and G alpha13 localize in membrane and cytoplasmic fractions, respectively. Exogenously expressed G alpha12 and G alpha13 also localize in membrane and cytoplasmic fractions, respectively, in COS-7 cells. Stimulation of lysophosphatidic acid receptor coupled to G alpha13 markedly promotes the translocation of G alpha13 from cytoplasm to membrane. This different localization of G alpha12 and G alpha13 may explain some of the nonoverlapping actions of G alpha12 and G alpha13.     

Baculovirus expression of mammalian G protein alpha subunits.

Complementary DNAs encoding three subtypes of the alpha subunit (alpha i-1, alpha o and alpha s) of rat guanyl nucleotide regulatory proteins were used to construct recombinant baculoviruses which direct high-level expression of the corresponding proteins in cultured Sf9 insect cells. The expressed proteins were recognized by polyclonal antisera specific for the different alpha chains, and co-migrated with the native proteins from rat brain membranes in immunoblotting analyses. Soluble and particulate forms of all three immunoreactive alpha chains were observed following ultracentrifugation of cell lysates. Biosynthetic radiolabelling of infected cells with [35S]methionine or [3H]myristate showed that both soluble and particulate forms of alpha i-1 and alpha o were myristoylated; in contrast, alpha s did not incorporate myristate. The soluble fractions from cells expressing alpha chains showed high levels of GTP-binding activity over that observed in uninfected cells, or in cells infected with wild-type virus. The peak expression levels observed at 72 h post-infection were highest for alpha o at ca. 400 pmol of GTP-gamma-35S/mg protein, or roughly 2% of the total soluble protein. The results of this work show that the baculovirus system can be employed for high-level production of mammalian G protein alpha chains which retain GTP-binding activity and are appropriately modified by myristoylation.     

Low parotid saliva calmodulin in patients with taste and smell dysfunction

Parotid saliva calmodulin was found both in 32 normal volunteers and in 60 patients with taste and smell dysfunction; salivary calmodulin concentration was significantly lower in the patients than in the volunteers. There were no differences in salivary calmodulin concentration with respect to age, sex, or salivary flow rate in either normal volunteers or patients. When patients were categorized by diagnosis, calmodulin concentration was found to be decreased in all patient groups. The concentration of calmodulin in saliva was about 10 times that found in serum, suggesting that the parotid gland is a major source of this protein.     

Shared and unique features of evolutionary diversification

A fundamental question in evolutionary biology asks whether organisms experiencing similar selective pressures will evolve similar solutions or whether historical contingencies dominate the evolutionary process and yield disparate evolutionary outcomes. It is perhaps most likely that both shared selective forces as well as unique histories play key roles in the course of evolution. Consequently, when multiple species face a common environmental gradient, their patterns of divergence might exhibit both shared and unique elements. Here we describe a general framework for investigating and evaluating the relative importance of these contrasting features of diversification. We examined morphological diversification in three species of livebearing fishes across a predation gradient. All species (Gambusia affinis from the United States of America, Brachyrhaphis rhabdophora from Costa Rica, and Poecilia reticulata from Trinidad) exhibited more elongate bodies, a larger caudal peduncle, and a relatively lower position of the eye in predator populations. This shared response suggests that common selective pressures generated parallel outcomes within three different species. However, each species also exhibited unique features of divergence, which might reflect phylogenetic tendencies, chance events, or localized environmental differences. In this system, we found that shared aspects of divergence were of larger magnitude than unique elements, suggesting common natural selective forces have played a greater role than unique histories in producing the observed patterns of morphological diversification. Assessing the nature and relative importance of shared and unique responses should aid in elucidating the relative generality or peculiarity in evolutionary divergence.     

Long life: a matter of taste (and smell)

Insulin/IGF signaling has emerged as a central regulator of metazoan aging. In C. elegans, insulin-like peptides are expressed predominately in neurons. Alcedo and Kenyon demonstrate that removal of specific gustatory and olfactory neurons result in longer life, suggesting that metazoan longevity is influenced by sensory perception.     

The sweet and the bitter of mammalian taste

The discovery of two families of mammalian taste receptors has provided important insights into taste recognition and taste perception. Recent studies have examined the receptors and signaling pathways that mediate sweet, bitter, and amino acid taste detection in mammals. These studies demonstrate that taste cells are selectively tuned to different taste modalities and clarify the logic of taste coding in the periphery.