Antennal Olfactory Neurons Research Articles

Rapid degeneration of Drosophila olfactory neurons in Orco mutant maxillary palps.

Drosophila melanogaster vinegar flies have two olfactory organs: the antenna and maxillary palp. Olfactory neurons in these tissues respond to odorants via odorant receptors. Insect odorant receptors are heterotetramers of two proteins: an odorant binding OrX subunit and an Odorant Receptor Co-Receptor (Orco). Mutation of Orco disrupts odorant receptor formation, and abolishes olfactory responses. Some antennal olfactory neurons in Orco mutants have been previously shown to degenerate. Here, we examine if maxillary palp olfactory neurons also degenerate in Orco mutants. We find degeneration occurs both more broadly and more rapidly in Orco mutant maxillary palp olfactory neurons than reported for antennae, with ~60% of all mutant olfactory neurons absent in maxillary palps by 7 days post eclosion. Interestingly, the subset of Orco mutant olfactory neurons that express the Or42a receptor appear resistant to degeneration. These results suggest the maxillary palp might be a suitable model for examining the molecular mechanisms underlying neurodegeneration in sensory neurons.

Microbial metabolites elicit distinct olfactory and gustatory preferences in bumblebees.

Animals such as bumblebees use chemosensory cues to both locate and evaluate essential resources. Increasingly, it is recognized that microbes can alter the quality of foraged resources and produce metabolites that may act as foraging cues. The distinct nature of these chemosensory cues however and their use in animal foraging remain poorly understood. Here, we test the hypothesis that species of nectar-inhabiting microbes differentially influence pollinator attraction and feeding via microbial metabolites produced in nectar. We first examined the electrophysiological potential for bumblebee (Bombus impatiens) antennal olfactory neurons to respond to microbial volatile organic compounds (mVOCs), followed by an olfactory preference test. We also assessed gustatory preferences for microbial-altered nectar through both no-choice and choice feeding assays. Antennal olfactory neurons responded to some mVOCs, and bees preferred nectar solutions inoculated with the bacterium Asaia astilbes over the yeast Metschnikowia reukaufii based on volatiles alone. However, B. impatiens foragers consumed significantly more Metschnikowia-inoculated nectar, suggesting distinct roles for mVOCs and non-volatile metabolites in mediating both attraction and feeding decisions. Collectively, our results suggest that microbial metabolites have significant potential to shape interspecific, plant-pollinator signalling, with consequences for forager learning, economics and floral host reproduction.

Behavioural responses of Anopheles gambiae sensu stricto to components of human breath, sweat and urine depend on mixture composition and concentration

Host-seeking behaviour of the anthropophilic malaria vector Anopheles gambiae sensu stricto (Diptera: Culicidae) is mediated predominantly by olfactory cues. Several hundreds of odour components have been identified from human emanations, but only a few have been proven to act as attractants or synergists in the host-seeking behaviour of female An. gambiae. In previous work, aromatics, alcohols and ketones in human odours were found to elicit electrophysiological activity in antennal olfactory neurons of female An. gambiae. However, the behavioural effects of these compounds have not been investigated. In this study, behavioural responses of female An. gambiae to components of human breath, urine and sweat at a series of concentrations, or a single concentration in the case of acetone, were examined in combination with ammonia and L-lactic acid in a dual-choice olfactometer. The results showed that at specific concentrations 4-ethylphenol, indole, 3-methyl-1-butanol and two ketones inhibited the attractive effect of a mixture of ammonia and lactic acid. Acetone on its own was not attractive; however, when combined with lactic acid, the binary mixture was attractive. When combined with ammonia, acetone inhibited the attractiveness exerted by ammonia alone. Dodecanol and dimethyldisulphide did not affect the attraction exerted by ammonia and lactic acid at any of the concentrations tested. By contrast, a human-specific armpit odour, 7-octenoic acid, augmented the attraction exerted by the combination of ammonia and lactic acid at a specific dosage.

Sensitivities of antennal olfactory neurons of the malaria mosquito, Anopheles gambiae, to carboxylic acids

Single sensillum recordings on the antennae of female Anopheles gambiae s.s. mosquitoes revealed neurons sensitive to aliphatic carboxylic acids within (a) subtype(s) sensilla trichodea. The aliphatic acids, acetic acid, propionic acid, butyric acid, iso-butyric acid and iso-valeric acid evoked an inhibition reaction in one of the cell types recorded from. A different cell type was excited in response to the former aliphatic acids, but showed a broader range of sensitivity, as acids with a longer carbon chain length, like caproic acid, elicited excitations as well. In addition, occasionally 1-octen-3-ol elicited an excitation reaction. This article focuses on the carboxylic acid inhibited cell type and its temporal pattern of response to different doses of the compounds. Furthermore, in order to compare the stimulatory effectiveness of the compounds on a per molecule basis, corrections were made for differences in volatility by determining the absolute number of molecules in the stimulus puff.

Receptor chirality and behavioral specificity of the boll weevil,Anthonomus grandis Boh. (Coleoptera: Curculionidae), for its pheromone, (+)-grandisol

Electrophysiological recordings from antennal olfactory receptors and field behavioral experiments showed both male and female boll weevils,Anthonomus grandis Boh. (Coleoptera: Curculionidae), to respond specifically to (+)-grandisol, an enantiomer of compound I of the boll weevil aggregation pheromone. Single-cell recordings revealed antennal olfactory neurons in both male and female weevils keyed to (+)-grandisol. Electroantennograms in response to serial dilutions of the grandisol enaniiomers showed a threshold 100 to 1000 times lower for (+)-grandisol relative to its antipode. In field behavioral experiments, both sexes were significantly more attracted to (+)-grandisol in combination with the three other pheromone components than the combination with (-)-grandisol. When (-)-grandisol was placed with the (+)-enantiomer at equal dosages, a slight although statistically insignificant inhibition occurred. Subsequent field tests showed that the low level of attraction exhibited by (-)-grandisol in combination with the other three pheromone components could be attributed to the other three components alone. These results are in contrast with an earlier study, which found (-)-grandisol to be as attractive as the (+)-enantiomer.