Ichiro Shimada

Genetic dimorphism in the taste sensitivity to trehalose inDrosophila melanogaster

SummaryA quantitative behavioral assay was developed for the measurement of taste responses to sugars inDrosophila. The amount of the intake of a sugar solution was measured colorimetrically after homogenization of flies which had consumed sugar solutions mixed with a food-dye. A two-choice method was utilized to determine the taste sensitivity to sugars. Two kinds of sugar solutions were marked with either blue or red food-dye and placed alternately in the wells of a micro test plate. Flies were allowed to choose between the two sugar solutions. By classifying and counting the coloured flies, the relative taste sensitivity could be determined. Employing these methods, a genetic dimorphism in the taste sensitivity to trehalose was found among some laboratory strains ofDrosophila melanogaster. No difference in the taste sensitivity to glucose, fructose and sucrose was found between the trehalose high-sensitivity (T-1) and the low-sensitivity (Oregon-R) strains. Trehalose concentration equivalent to 2 mmol/1 sucrose, in terms of stimulating activity, was 57 mmol/1 inOregon-R and was 10 mmol/1 inT-1. Genetic analysis showed that theTre gene, whose locus is closely linked tocx (13.6) on theX chromosome, is responsible for the difference in the taste sensitivity to trehalose.

Multiple receptor proteins for sweet taste inDrosophila discriminated by papain treatment

SummaryTreatment of the labellar chemosensory setae of the fruit fly,Drosophila melanogaster, with 0.1 % papain for 3 min induced a complete elimination of the taste nerve response to fructose (Fig. 1). Responses to other sugars examined were not affected (Table 1). Responses to 20 mM LiCl and 0.1 M NaCl also remained unchanged by the treatment. The experiment on the time-dependency of the papain treatment showed a clear difference in the proteasesensitivity between the response to fructose and to glucose and sucrose (Fig. 2). The treatment with 0.005% trypsin for 3 min produced the same results. The response to fructose which was eliminated with the papain treatment, was restored after 3 hrs. These findings reveal the presence of a specific receptor site for fructose and its protease-sensitive nature and suggest the involvement of multiple receptor proteins in the sugar receptor ofDrosophila.

The specific receptor site for aliphatic carboxylate anion in the labellar sugar receptor of the fleshfly

Abstract A two minute treatment of a single sugar receptor cell with 10 mg/ml pronase did not affect its response to d -fructose, but depressed markedly its response to l -valine. This is the first direct evidence for a specific site for certain aliphatic amino acids. All six amino acids that can stimulate the sugar receptor were examined and classified into two groups according to the presence or absence of the inhibitory effects of pronase treatment. Responses to certain aliphatic amino acids and a corresponding fatty acid were depressed whereas responses to phenylalanine and trytophan were not. Further evidence for the existence of two classes of amino acids comes from the fact that the α amino group of valine is not essential whereas that of phenylalanine is. It was concluded that the first class of amino acids react with a specific receptive site for carboxylate anions whereas the second react with the furanose site.

Treatment with pronase uncouples water and sugar reception in the lahellar water receptor of the blowfly

Summary1.The electrophysiology of labellar taste hairs ofPhormia terraenovae (Diptera, Calliphoridae) was investigated. Treatment of the hairs for 1–2 min with 10 mg/ml pronase E totally depresses the response of the water receptor to water and there is no sign of recovery within 1 h. On the other hand, the response of the water receptor, as well as of the sugar receptor, to D-fucose is hardly affected. This means that water and sugar reception in the water receptor happen at different sites of the dendritic membrane, and that proteins are involved in the process of water reception.2.Dose-response curves of the water and sugar receptor for D-fucose are similar after treatment with pronase. This means that the water receptor behaves as a typical sugar receptor if water reception is suppressed.3.Responses of the water and sugar receptor to various other sugars after treatment with pronase are similar in both receptors: responses to sugars which bind to the pyranose site of the sugar receptor are suppressed, whereas responses to D-fucose and D-fructose which bind to the furanose site of the sugar receptor are almost unaffected. This means that the sugar site of the water receptor has the same properties as the furanose site of the sugar receptor.4.The total depression of water and sugar receptor responses to D-galactose after treatment with pronase suggests that this sugar does not bind to the furanose site as has been believed up till now. The effect of pronase treatment on the response of the sugar receptor to 4-nitrophenyl-α-glucoside is a moderate depression followed within an hour by an activation. This suggests that the receptor site for this substance has other properties than the pyranose or the furanose site.5.The results confirm the concept of ‘multiple receptor sites’ and show for the first time that the same type of receptor site may be expressed in different chemoreceptor cells.

A temporal model of animal behavior based on a fractality in the feeding of Drosophila melanogaster

We present a new temporal model of animal behavior based on the ethological idea that the internal states of the individual essentially determine the behavior. The internal states, however, are conditioned by the external stimuli. This model, including environmental and internal parameters, predicts a fractal property of the behavior, that is, an inverse power law distribution of the duration. Being consistent with the model, we have found a fractal property of feeding in Drosophila melanogaster: The dwelling time of starved flies on food showed a clear inverse power law distribution. The dependence of the fractal dimension on the intensity of food stimuli has been observed, and the predicted change into an exponential distribution was proved.

Temporal fractal in the feeding behavior ofDrosophila melanogaster

A temporal fractal is clearly shown in the feeding behavior ofDrosophila as a self-similar pattern of locomotive velocity and inverse power law distributions of food dwelling time over the time scale range of 103. The fractality was observed in the dwelling time distribution immediately after the fly was placed to feeding site or on inferior food in a two-choice situation. Fractality may be understood as adaptive, and an intrinsic property of animal behavior that reflects complex information processing in the CNS ofDrosophila.

Taste response to 2,5-anhydro-d-hexitols; rigid stereospecificity of the furanose site in the sugar receptor of the flesh fly

Summary2,5-Anhydro-d-mannitol with a fixed furanose ring stimulated the sugar receptor of the flesh fly (Fig. 1) and reacted with the furanose site (Fig. 3). This is the first direct evidence that a furanose can stimulate the sugar receptor and supports strongly the assumption thatβ-d-fructofuranose is the only stimulatory component in the solution ofd-fructose.Rigid stereospecificity of the furanose site in the sugar receptor is discussed according to the effectiveness of various synthetic 2,5-anhydro-d-hexitols and related compounds (Table 2, Fig. 6).At least four receptor sites are concluded to be in a single sugar receptor: a pyranose (P) site, a furanose (F) site, an aliphatic carboxylate (R) site and an aromatic amino acid (Ar) site.

Memory effects on scale-free dynamics in foraging Drosophila

The fruit fly, Drosophila melanogaster, displays a scale-free behavior in foraging, i.e., the dwell time on food exhibits a power law distribution. The scaling exponent is generally believed to be stable and the significance of the exponent itself with respect to the scale-free behavior remains elusive. We propose a model whereby the scaling exponent of the scale-free behavior of an animal depends on the memory of the individual. The proposed model is based on the premise that animal behaviors are associated with internal states of the animal. The changes in the scaling exponent are derived by considering losing memory as increasing uncertainty, which is expressed in terms of information entropy of the internal states. Predicted model behaviors agree with experimental results of foraging behavior in wild-type and learning/memory Drosophila mutants. The concept of changes in the scaling exponent due to the amount of memory provides a novel insight into the emergence of a scale-free behavior and the meaning of the scaling exponent.

Cyclic AMP-dependent memory mutants are defective in the food choice behavior of Drosophila

Acute choice behavior in ingesting two different concentrations of sucrose in Drosophila is presumed to include learning and memory. Effects on this behavior were examined for four mutations that block associative learning (dunce, rutabaga, amnesiac, and radish). Three of these mutations cause cyclic AMP signaling defects and significantly reduced taste discrimination. The exception was radish, which affects neither. Electrophysiological recordings confirmed that the sensitivity of taste receptors is almost indistinguishable in all flies, whether wild type or mutant. These results suggest that food choice behavior in Drosophila involves central nervous learning and memory operating via cyclic AMP signaling pathways.

N-Acylation of stimulatory amino acids changes chiral recognition of the fleshfly labellar sugar receptor

SummaryN-Acylation changed nonstimulatory Dvaline into a clear stimulant of the sugar receptor of the fleshfly,Boettcherisca peregrina. Of theN-acyl-D-valines, the most stimulatory wasN-acetyl-D-valine. Similar changes into stimulants were also observed in other aliphatic amino acids such as leucine and methionine. Dose-response curves ofN-acetyl-D-valine suggested an increase of binding affinity, compared with that ofN-acetyl-L-valine. By treatment experiment with pronase 10 mg/ml, stimulatoryN-acetyl-D-amino acids were suggested to react with the specific alkyl site (R site), which was presumed to discriminate between L- and D-forms of the amino acids through steric hindrance between its own spatial barrier and D-amino acids (Shimada and Isono 1978; Shimada and Tanimura 1981).This change of chiral recognition cannot be explained by simple steric hindrance at the R site. It means, instead, that a hydrophobic subsite rather than a spatial barrier must be postulated.