Response plasticity of Drosophila olfactory sensory neurons

In insect olfaction, sensitization refers to the amplification of a weak olfactory signal when the stimulus is repeated within a specific time window. In the vinegar fly, Drosophila melanogaster, his occurs already at the periphery, at the level of olfactory sensory neurons (OSNs) located in the antenna. In our study, we investigate whether sensitization is a widespread property in a set of seven types of OSNs, as well as the mechanisms involved. First, we characterize and compare differences in spontaneous activity, response velocity and response dynamics among the selected OSN types. These express different receptors with distinct tuning properties and behavioral relevance. Second, we show that sensitization is not a general property. Among our selected OSNs types, it occurs in those responding to more general food odors, while OSNs involved in very specific detection of highly specific ecological cues like pheromones and warning signals show no sensitization. Moreover, we show that mitochondria play an active role in sensitization by contributing to the increase in intracellular Ca2+ upon weak receptor activation. Thus, by using a combination of single sensillum recordings (SSR), calcium imaging and pharmacology, we widen the understanding of how the olfactory signal is processed at the periphery.Abstract Figure

Arrestin-mediated Desensitization Enables Olfactory Discrimination in C. elegans

In the mammalian olfactory system, crosstalk among diverse olfactory signals is minimized through labelled line coding: individual neurons express one or few olfactory receptors among those encoded in the genome. Labelled line coding allows for separation of stimuli during mammalian olfactory signal transduction, however, in the nematode worm Caenorhabditis elegans, 1,300 olfactory receptors are primarily expressed in only 32 neurons, precluding this strategy. Here we report genetic, pharmacological and behavioural evidence that β-arrestin-mediated desensitization of olfactory receptors, working downstream of the kinase GRK-1, enables discrimination between intra-neuronal olfactory stimuli, but that this discrimination relies on quantitative, rather than qualitative differences in signalling. Our findings suggest that C. elegans exploits β-arrestin desensitization to maximize responsiveness to novel odors, allowing for behaviourally appropriate responses to olfactory stimuli despite the large number of olfactory receptors signalling in single cells. This represents a fundamentally different solution to the problem of olfactory discrimination than that which evolved in mammals, allowing for economical use of an extremely limited number of sensory neurons.

Nocturnal scent in a ‘bird-fig’: a cue to attract bats as additional dispersers?

The plant genus Ficus is a keystone resource in tropical ecoystems. One of the unique features of figs is the diversity of fruit traits, which in many cases match their various dispersers, the so-called fruit syndromes. The classic example of this is the strong phenotypic differences found between figs with bat and bird dispersers (color, size, and presentation). The ‘bird-fig’ Ficus colubrinae represents an exception to this trend since it attracts the small frugivorous bat species Ectophylla alba at night, but during the day attracts bird visitors. Here we investigate the mechanism by which this ‘bird-fig’ attracts bats despite its fruit traits, which should appeal solely to birds. We performed feeding experiments with Ectophylla alba to assess the role of fruit scent in the detection of ripe fruits. Ectophylla alba was capable of finding ripe figs by scent alone under exclusion of other sensory cues. This suggests that scent is the main foraging cue for Ectophylla alba. Analyses of odor bouquets from the bat- and bird-dispersal phases (i.e. day and night) differed significantly in their composition of volatiles. The combination of these two findings raises the question whether E. alba and F. colubrinae resemble a co-adaptation that enables a phenotypically classic ‘bird-fig’ to attract bat dispersers by an olfactory signal at night thus maximizing dispersal.