Roberto Massimo Crnjar

Genetic sensitivity to the bitter taste of 6-n-propylthiouracil (PROP) and its association with physiological mechanisms controlling body mass index (BMI).

Taste sensitivity to the bitter compound 6-n-propylthiouracil (PROP) is considered a marker for individual differences in taste perception that may influence food preferences and eating behavior, and thereby energy metabolism. This review describes genetic factors that may contribute to PROP sensitivity including: (1) the variants of the TAS2R38 bitter receptor with their different affinities for the stimulus; (2) the gene that controls the gustin protein that acts as a salivary trophic factor for fungiform taste papillae; and (3) other specific salivary proteins that could be involved in facilitating the binding of the PROP molecule with its receptor. In addition, we speculate on the influence of taste sensitivity on energy metabolism, possibly via modulation of the endocannabinoid system, and its possible role in regulating body composition homeostasis.

Marked Increase in PROP Taste Responsiveness Following Oral Supplementation with Selected Salivary Proteins or Their Related Free Amino Acids

The genetic predisposition to taste 6-n-propylthiouracil (PROP) varies among individuals and is associated with salivary levels of Ps-1 and II-2 peptides, belonging to the basic proline-rich protein family (bPRP). We evaluated the role of these proteins and free amino acids that selectively interact with the PROP molecule, in modulating bitter taste responsiveness. Subjects were classified by their PROP taster status based on ratings of perceived taste intensity for PROP and NaCl solutions. Quantitative and qualitative determinations of Ps-1 and II-2 proteins in unstimulated saliva were performed by HPLC-ESI-MS analysis. Subjects rated PROP bitterness after supplementation with Ps-1 and II-2, and two amino acids (L-Arg and L-Lys) whose interaction with PROP was demonstrated by 1H-NMR spectroscopy. ANOVA showed that salivary levels of II-2 and Ps-1 proteins were higher in unstimulated saliva of PROP super-tasters and medium tasters than in non-tasters. Supplementation of Ps-1 protein in individuals lacking it in saliva enhanced their PROP bitter taste responsiveness, and this effect was specific to the non-taster group.1H-NMR results showed that the interaction between PROP and L-Arg is stronger than that involving L-Lys, and taste experiments confirmed that oral supplementation with these two amino acids increased PROP bitterness intensity, more for L-Arg than for L-Lys. These data suggest that Ps-1 protein facilitates PROP bitter taste perception and identifies a role for free L-Arg and L-Lys in PROP tasting.

Morphological and electrophysiological mapping of tarsal chemoreceptors of oviposition-deterring pheromone in Rhagoletis pomonella flies

Abstract Light microscopy and S.E.M. observations revealed that Rhagoletis pomonella female tarsi, bearing the principal receptors of oviposition-deterring fruit marking pheromone (ODP), have 3 types of chemosensilla: B, C and D. Using electrophysiological hair tip-recording techniques, we found that D chemosensilla located in pairs on distal ventrolateral portions of the 2nd, 3rd and 4th tarsomeres of each leg were highly sensitive to stimulation by the pheromone. D chemosensilla located in pairs on the 5th tarsomere of each leg were moderately sensitive to the pheromone, while the B and C chemosensilla of all tarsi were nearly or completely insensitive to it. For reasons discussed, the D chemosensilla on the prothoracic tarsi may be the most important in providing sensory input eliciting oviposition deterrence.

Associations between Orosensory Perception of Oleic Acid, the Common Single Nucleotide Polymorphisms (rs1761667 and rs1527483) in the CD36 Gene, and 6-n-Propylthiouracil (PROP) Tasting

Orosensory perception of dietary fat varies in individuals, thus influencing nutritional status. Several studies associated fat detection and preference with CD36 or 6-n-propylthiouracil (PROP) sensitivity. Other studies have not confirmed the latter association. We analyzed the relationship between orosensory perception of oleic acid, two CD36 variants, and PROP tasting. Thresholds of oleic acid perception were assessed in 64 subjects using a modification of the three-alternative forced-choice procedure. Subjects were classified for PROP taster status and genotyped for TAS2R38 and CD36 (SNPs: rs1761667 and rs1527483). Subjects homozygous for GG of the rs1761667 polymorphism showed higher sensitivity to oleic acid than AA subjects. The capability to detect oleic acid was directly associated with TAS2R38 or PROP responsiveness. PROP non-tasters had a lower papilla density than tasters, and those with genotype GG of the rs1761667 polymorphism had lower oleic acid thresholds than PROP non-tasters with genotype AA. In conclusion, results showed a direct association between orosensory perception of oleic acid and PROP tasting or rs1761667 polymorphism of CD36, which play a significant role in PROP non-tasters, given their low number of taste papillae. Characterization of individual capability to detect fatty acids may have important nutritional implications by explaining variations in human fat preferences.

An endocrine control mechanism for chemosensillar activity in the blowfly

Juvenile hormone (JH) administration increases the sensitivity of labellar chemosensilla inPhormia. It is suggested that this hormone plays a role in controlling both chemosensillar sensitivity and ovarian cycles.

The gustin (CA6) gene polymorphism, rs2274333 (A/G), is associated with fungiform papilla density, whereas PROP bitterness is mostly due to TAS2R38 in an ethnically-mixed population.

PROP responsiveness is associated with TAS2R38 haplotypes and fungiform papilla density. Recently, we showed that a polymorphism in the gene coding for the salivary trophic factor, gustin (CA6), affects PROP sensitivity by acting on cell growth and fungiform papillae maintenance, in a genetically homogeneous cohort. Since population homogeneity can lead to over estimation of gene effects, the primary aim of the present work was to confirm gustins role in PROP bitterness intensity and fungiform papillae density in a genetically diverse population. Eighty subjects were genotyped for both genes by PCR techniques. PROP responsiveness was assessed by a filter paper method and fungiform papilla density was determined in each subject. As expected, PROP bitterness ratings were lower in individuals with the AVI/AVI diplotype of TAS2R38 than in individuals with PAV/PAV and PAV/AVI diplotypes. However, no differences in PROP bitterness among genotypes of the gustin gene, and no differences in the density of fungiform papillae related to TAS2R38 diplotype were found. In contrast, the density of fungiform papillae decreased as the number of minor (G) alleles at the gustin locus increased. In addition, the distribution of TAS2R38 genotypes within each gustin genotype group showed that the occurrence of recessive alleles at both loci was infrequent in the present sample compared to other populations. These findings confirm that papillae density is associated with gustin gene polymorphism, rs2274333 (A/G), in an ancestrally heterogeneous population, and suggest that variations in the frequency of allele combinations for these two genes could provide a salient explanation for discrepant findings for gustin gene effects across populations.

Influence of age on the electroantennogram response of the female blowfly (Phormia regina) (Diptera: Calliphoridae)

Abstract By means of electroantennogram recording techniques, we have monitored the antennal olfactory sensitivity, from the time of eclosion until complete egg maturation, of female blowflies (Phormia regina) fed either a protein diet or a protein free one. The tested stimuli were swormlure-4 (SL-4) which is a potent lure for calliphorid flies, 1-hexanol as a reference stimulus and air as a control. After taking the electroantennograms, egg and ovarian development were evaluated. Stimulation with SL-4 and 1-hexanol evoked electroantennograms increasing in amplitude with age regardless of whether or not flies were fed protein during the first 5 days of adult life. In the protein-fed flies eggs were fully developed whereas those of the no-protein group remained undeveloped. The peak olfactory sensitivity occurs at a time when the female fly begins to search for an oviposition substrate.

Morphology and EAG mapping of the antennal olfactory receptors in Dacus oleae

EAGs were recorded from various locations on the flagellar surface of the antennae of the olive fly Dacus oleae stimulated with compounds of behavioural significance to this species. This information was compared with data on the typology and distribution patterns of the olfactory sensilla. Results showed that: a) 3 types of olfactory sensilla are present on the antennae: long basiconica, short grooved basiconica and trichodea; b) 1‐hexanol, ethanol and volatiles belonging to the oily fraction of the olive pulp are the strongest stimuli, while those of the water fraction are little or not effective; c) EAG amplitude values vary as a function of the recording location on the flagellar surface; d) a significant correlation was found, for 2 stimuli of the oily fraction, between EAG amplitude and population density of long sensilla basiconica, thus suggesting this type as specifically responding to these substances.

Applying the IUCN threat categories to island endemics: Sardinian butterflies (Italy)

European nature conservation documents, often reflect the charisma of a species rather than its actual degree of threat. The assessment of the threat status of 14 endemic Sardinian butterfly species, underlines that European nature legislation documents are incomplete. Pseudophilotes barbagiae and Lysandra coridon gennargenti (Lycaenidae) are identified as globally Vulnerable and are therefore proposed to be added to the Red Data Book of European butterflies as species of global conservation concern. A threat factor analysis identifies risks towards butterflies in Sardinia arising from increasing human activities. It is shown how the quantitative information used by the IUCN criteria, together with a qualitative assessment of human induced threat factors, could be combined to produce an objective standardised assessment that can be used also when only data on present distribution are available. Threats to Sardinian butterflies are highlighted and conservation measures proposed. The inclusion of Pseudophilotes barbagiae and Lysandra coridon gennargenti in Annex II and IV of the European Habitats Directive, and in Appendix II of the Bern Convention, is strongly recommended.

Sensitivity of the mosquito Aedes aegypti (Culicidae) labral apical chemoreceptors to phagostimulants

The feeding of Aedes aegypti (L.) on blood and nectar is induced by phagostimulants: adenine nucleotides and sugars respectively. This work examines the responses of the four chemoreceptor cells in the labral apical sensilla to these phagostimulants. The apical chemoreceptors can detect the presence of adenine nucleotides. This part of the response is in good agreement with the gorging behavior. The output of the chemoreceptors cannot distinguish among different adenine nucleotides or among their concentrations (0.01-1 mmol/l), whereas gorging behavior is affected by the identity of adenine nucleotides and by their concentrations. Hence the gorging behavior cannot be driven by the output of these chemoreceptors alone. To the presence of adenine nucleotides Cell 2 was the only cell that responded with high frequencies, while the response of Cell 4 was almost abolished. The response of Cell 2 to ATP depended on the mosquitos physiological state. This dependence accorded well with the gorging behavior; Cell 2 responded with a higher frequency to ATP in the gorging state, than when not in a gorging state. The responses to sucrose and fructose constituted the only case recorded in which all these chemoreceptors failed to respond. This depression of response implies that other chemoreceptors must be present as sugar detectors.