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These findings will form the foundation for a systems-level
understanding of odor coding that spans from the molecular to
neuronal level. Acknowledgements: Citrus Research Board
#P205
POSTER SESSION V:
TRIGEMINAL SYSTEM; BEHAVIOR
AND PSYCHOPHYSICS; ODORANT
RECEPTORS & OLFACTION PERIPHERY
An Odorant Receptor Mediating Attraction of
Drosophila melanogaster to a Specific Enantiomer of a
Food Derived Odorant
Wilfredo Escala, Andrew S. Nichols, R. Grace Zhai,
Charles W. Luetje
Molecular & Cellular Pharmacology, University of Miami,
Miami, FL, USA
Odorant receptors (ORs), a family of odorant-gated ion channels,
mediate the attraction of
D. melanogaster
to a variety of fruits.
Ethyl-3-hydroxybutyrate (E3HB), a component of fruit extracts that
activates several
Drosophila
ORs, is chiral, with the S isomer
preferentially produced by yeast through reduction of ethyl
acetoacetate, also a component of fruit extracts. Because yeast
growing on fruit is a primary food source for
Drosophila
and
S-E3HB may serve as a marker for the presence of yeast, we asked
whether flies could distinguish between the isomers of E3HB.
In a preference assay, adult female flies showed an innate
preference for the S isomer. In an aversive associative conditioning
assay, we also found that flies could distinguish between the two
isomers and be conditioned to prefer the R isomer by associating
R-E3HB with sweet taste (sucrose) and S-E3HB with bitter taste
(quinine). To determine which OR mediates this behavior we
expressed in
Xenopus
oocytes several ORs (9a, 35a, 85a, 85b)
previously shown to respond to racemic E3HB and assayed by
electrophysiology (Orco was coexpressed). While Or35a showed a
slight preference for the R isomer, and Or9a and Or85b showed no
preference, Or85a displayed a >1000-fold preference for the S
isomer. Next we asked whether Or85a was responsible for the
ability of flies to distinguish isomers of E3HB. Using the
UAS/GAL4 approach to selectively express tetanus toxin, we
found that silencing Or85a expressing olfactory sensory neurons
eliminated the ability to distinguish between isomers, while
silencing Or9a expressing neurons did not affect the ability of the
flies to distinguish between isomers. We conclude that Or85a plays
an essential role in recognizing the presence of S-E3HB, a potential
food source marker for
Drosophila melanogaster
.
Acknowledgements: NIH RO1DC011091
#P206
POSTER SESSION V:
TRIGEMINAL SYSTEM; BEHAVIOR
AND PSYCHOPHYSICS; ODORANT
RECEPTORS & OLFACTION PERIPHERY
Temporal features of odor stimuli and the encoding of odor
identity and intensity by Olfactory Receptor Neurons
Carlotta Martelli, John R Carlson, Thierry Emonet
Yale/MCDB New Haven, CT, USA
Odor stimuli are detected by Olfactory Receptor Neurons (ORNs)
that project to segregated regions of the brain called glomeruli,
where they make synaptic connections with second-order neurons.
Different odorants elicit distinct patterns of activity in the
population of ORNs as well as in the glomeruli, suggesting that
odors are encoded in spatial combinatorial maps. Odors also elicit
diverse temporal patterns of activity at several levels of the
olfactory system but their origin and role in odor coding remains so
far unclear. We performed single sensillum recordings from the
Drosophila
antenna simultaneously with measurements of the
odorant concentration reaching the fly. We found that in several
conditions stimulus dynamics depends on odor type before any
interaction with the olfactory system occurs. Individual ORNs
follow these differences in stimulus dynamics with such precision
that a linear-nonlinear model can predict the response of one ORN
to different odorants solely from measurements of the stimulus.
This suggests that a single response function can be associated to a
single ORN and mediates the response to a large set of different
odors. Importantly we found that ORN adaptation capabilities
maintain response dynamics remarkably similar across
a large range of stimulus and background intensities. Hence,
irrespective of the odor and receptor type, ORNs can capture
information about stimulus dynamics independently from the
intensity of the signal. Our results open the question of whether
odor-specific dynamics might be used in discrimination tasks and
affect odor tracking strategies. Acknowledgements: This work was
supported by research awards from the Whitehall Foundation and
the Raymond and Beverley Sackler Institute for Biological,
Physical and Engineering Sciences to T.E., and by NIH
grants to J.C.
#P207
POSTER SESSION V:
TRIGEMINAL SYSTEM; BEHAVIOR
AND PSYCHOPHYSICS; ODORANT
RECEPTORS & OLFACTION PERIPHERY
Linking Ecological Adaptations in Olfactory Physiology and
Functional Genetics of Olfactory Receptors in a Polyphagous
female Moth,
Spodoptera littoralis
Muhammad Binyameen
1
, William B Walker III
1
, Nicolas
Montagne
2
, Christelle Monsempes
3
, David Carrasco
1
,
Rickard Ignell
1
, Fredrik Schlyter
1
, Bill S Hansson
1,4
,
Emmanuelle Jacquin-Joly
3
, Peter Anderson
1
, Mattias C Larsson
1
1
Swedish University of Agricultural Sciences Alnarp, Sweden,
2
UMR PISC, Université Paris 6 Paris, France,
3
National Institute
of Agronomic Research (INRA) Versailles, France,
4
Max Planck
Inst for Chemical Ecology Jena, Germany
Host plant selection is of continuous ecological and evolutionary
interest with respect to understanding host specialization,
speciation, and the steady emergence of insect pests in our
agro-ecosystems. We have selected a polyphagous and widespread
agricultural pest, the Egyptian Cotton Leaf Worm moth
Spodoptera
littoralis
, as a research model to elucidate olfactory neural
mechanisms related to host plant selection. We are characterizing
olfactory receptor (OR) genes, recently identified in
S. littoralis
.
The receptive range of each odorant receptor is determined via de-
orphanisation experiments in a heterologous expression system.
Individual olfactory receptor proteins are expressed in the vinegar
fly
Drosophila melanogaster
, and their response profiles
characterized by means of single neuron electrophysiological
recordings. We study how ecological adaptations in olfactory
genetics and physiology are linked in
S. littoralis
, and we will also
determine how much the level of differentiation is between
olfactory receptor populations of different moth species (sequence
polymorphism, differential expression, and functional receptive
range) to study how olfactory function and behavioral preferences
may co-evolve. We show that the heterologous expression system
works very well, and we have identified ORs that respond to odors
96 | AChemS Abstracts 2012
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