Impact of probiotics on development and behaviour in Drosophila melanogaster - a potential in vivo model to assess probiotics.

In vitro models are frequently used in probiotic research. However, such models often fail to predict in vivo functionality and efficacy. This fact complicates the screening process for selecting the most suitable strains, prior to accomplish expensive animal studies and clinical intervention trials. Therefore, additional sensitive, discriminating and cost-effective models are needed to conduct preliminary assays before undertaking human intervention studies definitely proving efficacy. With this purpose in mind, we explored the potential of axenic Drosophila melanogaster populations as well as of these axenic flies treated with probiotic microbial strains as a model to test the effects of probiotics on a subset of developmental and behavioural traits. An axenic D. melanogaster progeny from the wild-type Canton S strain was obtained and its eggs were further developed until pupae eclosion occurred in growth medium containing either of two probiotic strains: Bifidobacterium animalis subsp. lactis Bb12 or Lactobacillus rhamnosus GG. Whereas B. animalis Bb12 colonised the flies, the capacity of L. rhamnosus LGG to colonise was considerably lower in our experimental conditions. Regarding the influence of microbial load on the flies' development, the axenic condition caused a decrease in egg survival, and lowered adults' average weight with respect to wild-type flies. Both probiotics were able to counteract these effects. An earlier emergence of adults was observed from eggs treated with L. rhamnosus GG in comparison to the other fly populations. The axenic condition did not influence negative geotaxis behaviour in Drosophila; however, flies mono-associated with B. animalis Bb12 moved faster than wild-type. Our results suggest that the use of axenic/probiotic-treated D. melanogaster populations may be an affordable model for preliminary testing of the effects of probiotics on developmental or behavioural aspects.

Mutations affecting the cAMP transduction pathway modify olfaction in Drosophila.

The rutabaga and dunce genes, encode two enzymes of the cyclic adenosine monophosphate transduction pathway in Drosophila, adenylyl cyclase and cyclic adenosine monophosphate phosphodiesterase, respectively. Two main second messenger systems, depending on inositol 1,4,5-triphosphate and cyclic adenosine monophosphate, have been associated with olfaction in vertebrates as well as invertebrates. A relationship between the cyclic adenosine monophosphate signaling pathway and olfactory reception in Drosophila is suggested by the presence of cyclic nucleotide gated channels and cyclic-nucleotide modulated K+ channels in the antennae, the main olfactory organs. In this report, molecular, electrophysiological and behavioral data support the role of cyclic adenosine monophosphate in olfactory function for this species. Expression of both genes in the antennae has been shown by messenger ribonucleic acid analysis. Changes in the electroantennogram kinetics have been observed specifically on the slope of the initial rising phase, as predicted for processes that affect cyclic adenosine monophosphate concentration. Olfactory behavior changes due to both mutations were coherent with a functional meaning of the reported electrophysiological phenotype in olfactory perception. Sensitivity level increases or decreases for the mutants compared to the control line depending on the odorant. These results are compatible with some olfactory coding at the reception level by differential activation of a dual transduction system involving the inositol 1,4,5-triphosphate and cyclic adenosine monophosphate cascades.

Quantifying relative importance of maxillary palp information on the olfactory behavior of Drosophila melanogaster.

Maxillary palps have been proposed as secondary olfactory organs, after the antennae, in Drosophila melanogaster. Our study tries to establish the quantitative importance of both organs as olfactory information mediators. Dose-response curves for three odorants: ethyl acetate, propionaldehyde and benzaldehyde were carried out for comparing olfaction in either complete animals or flies surgically deprived of antennae. Antennaless flies tested in our behavioral assay showed indifferent, attractant and repellent responses depending on concentration, similarly as normal flies do. However, they clearly displayed less sensitivity than normal flies. The range of concentrations they were able to perceive was correlated to antennal sensitivity approximately by a factor 1:10 for ethyl acetate and benzaldehyde, and between 1:10 and 1:100 at high concentrations of propionaldehyde. A complementary experiment was performed to test changes in olfactory behavior produced by removing maxillary palps in the presence of antennae. At high concentrations of odorant, responses to ethyl acetate and propionaldehyde experienced small changes when both palps were removed. Results are compatible with a summation model of all olfactory information reaching the brain either through antennae or palps.

The rdgB gene of Drosophila: a link between vision and olfaction.

ota1 (ota = olfactory trap abnormal), an X-linked mutation of Drosophila isolated by virtue of abnormal olfactory behavior, is shown to be an allele of rdgB (retinal degeneration B), a gene required for normal visual system physiology. rdgB function is shown to be necessary for olfactory response of both adult flies and larvae, which have distinct olfactory systems. Electrophysiological recordings from the adult antenna indicate that rdgB is required for normal response in the peripheral olfactory system: some rdgB mutants show a delayed return to the resting potential following stimulation with ethyl acetate vapor. These results indicate that rdgB is required for both visual and olfactory physiology, and they suggest that visual and olfactory transduction may share at least one common molecular step in Drosophila.

Characterization of the electroantennogram in Drosophila melanogaster and its use for identifying olfactory capture and transduction mutants.

1. Amplitude as well as time course of the electroantennogram (EAG) in Drosophila has been used for describing electrical changes produced in the antenna in response to odorous stimulation. 2. Maximal amplitude of response appears to be directly correlated to stimulus concentration but, after achieving a maximum value, is independent of stimulation duration. 3. Rise time and fall time constants have been quantified for describing kinetics of response. The rise time constant decreases, but the fall time constant increases when increasing concentrations of odorant are supplied. 4. Variation among individuals for these EAG parameters is small enough to uncover even partial defects affecting the first sensory step. This fact combined with the possibility of obtaining mutants with defects in any intermediate process producing the electrical response makes the EAG of Drosophila a very useful tool for dissecting the components of the capture and transduction processes in the olfactory sense. 5. This kind of quantitative study of the EAG has been used in a new Drosophila mutant, od A, for localizing peripheral expression of the mutation. od A has been isolated as a behavioral mutant with an abnormally enhanced olfactory response to ethyl acetate. 6. The mutant's EAG in response to this odorant displays a normal amplitude but abnormal kinetics. Rise time as well as fall time show slower kinetics than normal, suggesting some defective step in the capture and transduction process.

Intrapopulational variation of olfactory responses in Drosophila melanogaster.

The existence of genetic variability for olfactory response within natural populations of Drosophila melanogaster was studied in two newly collected natural populations from two very different habitats, the Sandiche population, from a very heterogeneous environment, and the Los Areneros population, from a very homogeneous one. Intrapopulational variability was estimated over approximately 50 isofemale lines derived from each population. Results confirm significant differences in olfactory response to ethyl alcohol and acetaldehyde in both populations and to ethyl acetate in the Sandiche population. The differences were due partially to common components of the olfactory responses to different chemical (nonspecifics) in the Sandiche population, but they were specific for the stimulus in the Los Areneros population.

Genetical analysis of intrapopulational variation in olfactory response in Drosophila melanogaster.

Genetical study of olfactory response to ethyl alcohol (8 per cent) has been carried out on inbred lines extracted from a natural population using biometrical and chromosome analyses. A full diallel analysis was made in seven endogamic lines (3 high, 3 low and 1 intermediate in response values). Our results show a highly significant (P less than 0.001) additive component of variance and a less significant (P less than 0.05) directional dominance component suggesting overdominance and some endogamic depression. No significant maternal or reciprocal components of variation appear in our population. Two chromosome substitution assays among 3 inbred lines of extreme olfactory response add up information to the results of diallel analysis. The differences in response are due to chromosome III with an additive effect highly significant (P less than 0.001) in both studies. The other major chromosomes do not show any effect themselves but some interactions with chromosome III are significant. They can explain the directional dominance that we find in the diallel study. Analysed olfactory variation in response to ethanol can be considered as unspecific in relation to various chemical compounds.