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1.  Odor identity influences tracking of temporally patterned plumes in Drosophila 
BMC Neuroscience  2011;12:62.
Turbulent fluid landscapes impose temporal patterning upon chemical signals, and the dynamical neuronal responses to patterned input vary across the olfactory receptor repertoire in flies, moths, and locusts. Sensory transformations exhibit low pass filtering that ultimately results in perceptual fusion of temporally transient sensory signals. For example, humans perceive a sufficiently fast flickering light as continuous, but the frequency threshold at which this fusion occurs varies with wavelength. Although the summed frequency sensitivity of the fly antenna has been examined to a considerable extent, it is unknown how intermittent odor signals are integrated to influence plume tracking behavior independent of wind cues, and whether temporal fusion for behavioral tracking might vary according to the odor encountered.
Here we have adopted a virtual reality flight simulator to study the dynamics of plume tracking under different experimental conditions. Flies tethered in a magnetic field actively track continuous (non-intermittent) plumes of vinegar, banana, or ethyl butyrate with equal precision. However, pulsing these plumes at varying frequency reveals that the threshold rate, above which flies track the plume as if it were continuous, is unique for each odorant tested. Thus, the capability of a fly to navigate an intermittent plume depends on the particular odorant being tracked during flight. Finally, we measured antennal field potential responses to an intermittent plume, found that receptor dynamics track the temporal pattern of the odor stimulus and therefore do not limit the observed behavioral temporal fusion limits.
This study explores the flies' ability to track odor plumes that are temporally intermittent. We were surprised to find that the perceptual critical fusion limit, determined behaviorally, is strongly dependent on odor identity. Antennal field potential recordings indicate that peripheral processing of temporal cues faithfully follow rapid odor transients above the rates that can be resolved behaviorally. These results indicate that (1) higher order circuits create a perceptually continuous signal from an intermittent sensory one, and that (2) this transformation varies with odorant rather than being constrained by sensory-motor integration, thus (3) offering an entry point for examining the mechanisms of rapid olfactory decision making in an ecological context.
PMCID: PMC3145592  PMID: 21708035
2.  G-protein coupled Receptor Kinase 2 is required for rhythmic olfactory responses in Drosophila 
Current biology : CB  2008;18(11):787-794.
The Drosophila circadian clock controls rhythms in the amplitude of odor-induced electrophysiological responses that peak during the middle of night. These rhythms are dependent on clocks in olfactory sensory neurons (OSNs), which suggests that odorant receptors(ORs) or OR-dependent processes are under clock control. Since responses to odors are initiated by heteromeric OR complexes that form odor-gated and cyclic-nucleotide-activated cation channels, we tested whether regulators of ORs were under circadian clock control.
The levels of G-protein coupled receptor kinase 2 (Gprk2) mRNA and protein cycle in a circadian clock-dependent manner with a peak around mid-night in antennae. Gprk2 overexpression in OSNs from wild-type or cyc01 flies elicits constant high amplitude electroantennogram (EAG) responses to ethyl acetate, whereas Gprk mutants produce constant low amplitude EAG responses. Odorant receptors (ORs) accumulate to high levels in the dendrites of OSNs around mid-night, and this dendritic localization of ORs is enhanced by Gprk2 at times when ORs are primarily localized in the cell body.
These results support a model in which circadian clock-dependent rhythms in Gprk2 abundance control the rhythmic accumulation of ORs in OSN dendrites, which in turn control rhythms in olfactory responses. The enhancement of OR function by GPRK2 contrasts with the traditional role of Gprks in desensitizing activated receptors, and suggests that GPRK2 functions through a fundamentally different mechanism to modulate OR activity.
PMCID: PMC2474769  PMID: 18499458
3.  Spike amplitude of single unit responses in antennal sensillae is controlled by the Drosophila circadian clock 
Current biology : CB  2008;18(11):803-807.
Oscillators in olfactory sensory neurons (OSNs) are both necessary and sufficient to sustain rhythms in electroanntenogram (EAG) responses, which suggests that odorant receptors (ORs) and/or OR-dependent processes are under clock control. Since EAGs have limited spatial resolution and do not necessarily reflect firing of action potentials, we measured single unit responses in different antennal sensillae from wild-type, clock mutant, odorant receptor mutant, and G-protein coupled receptor kinase 2 (Gprk2) mutant flies to examine the cellular and molecular mechanisms that drive rhythms in olfaction. Spontaneous spike amplitude, but not spontaneous or odor induced firing frequency, is under clock control in ab1 and ab3 basiconic sensillae and T2 trichoid sensillae. Mutants lacking odorant receptors in dendrites display constant low spike amplitudes, and reducing or increasing levels of GPRK2 in OSNs results in constant low or high spontaneous spike amplitudes, respectively, in ab1, ab3 and T2 sensillae. We conclude that spike amplitude is controlled by circadian clocks in basiconic and trichoid sensillae, and requires GPRK2 expression and the presence of functional ORs in dendrites. These results argue that rhythms in GPRK2 levels control OR localization and OR-dependent ion channel activity/composition to mediate rhythms in spontaneous spike amplitude.
PMCID: PMC2474768  PMID: 18499459
4.  Nocturnal Male Sex Drive in Drosophila 
Current biology : CB  2007;17(3):244-251.
Many behaviors and physiological processes including locomotor activity, feeding, sleep, mating, and migration are dependent on daily or seasonally reoccurring, external stimuli [1–3]. In D. melanogaster, one of the best-studied circadian behaviors is locomotion. The fruit fly is considered a diurnal (day active/night inactive) insect, based on locomotor-activity recordings of single, socially naive flies [4, 5]. We developed a new circadian paradigm that can simultaneously monitor two flies in simple social contexts. We find that heterosexual couples exhibit a drastically different locomotor-activity pattern than individual males, females, or homosexual couples. Specifically, male-female couples exhibit a brief rest phase around dusk but are highly active throughout the night and early morning. This distinct locomotor-activity rhythm is dependent on the clock genes and synchronized with close-proximity encounters, which reflect courtship, between the male and female. The close-proximity rhythm is dependent on the male and not the female and requires circadian oscillators in the brain and the antenna. Taken together, our data show that constant exposure to stimuli emanating from the female and received by the male olfactory and other sensory systems is responsible for the significant shift in intrinsic locomotor output of socially interacting flies.
PMCID: PMC2239012  PMID: 17276917
5.  A Drosophila Nonvisual Arrestin Is Required for the Maintenance of Olfactory Sensitivity 
Chemical senses  2005;31(1):49-62.
Nonvisual arrestins are a family of multifunctional adaptor molecules that regulate the activities of diverse families of receptors including G protein–coupled receptors, frizzled, and transforming growth factor-β receptors. These activities indicate broad roles in both physiology and development for nonvisual arrestins. Drosophila melanogaster has a single nonvisual arrestin, kurtz, which is found at high levels within the adult olfactory receptor neurons (ORNs), suggesting a role for this gene in modulating olfactory sensitivity. Using heat-induced expression of a krz cDNA through development, we rescued krz1 lethality. The resulting adults lacked detectable levels of krz in the olfactory system. The rescued krz1 homozygotes have an incompletely penetrant antennal structural defect that was completely rescued by the neural expression of a krz cDNA. The krz1 loss-of-function adults without visible antennal defects displayed diminished behavioral responsiveness to both aversive and attractive odors and also demonstrated reduced olfactory receptor potentials. Both the behavioral and electrophysiological phenotypes were rescued by the targeted expression of the krz cDNA within postdevelopmental ORNs. Thus, krz is required within the nervous system for antennal development and is required later in the ORNs for the maintenance of olfactory sensitivity in Drosophila. The reduced receptor potentials in krz1 antenna indicate that nonvisual arrestins are required for the early odor-induced signaling events within the ORNs.
PMCID: PMC2180162  PMID: 16306316
adaptation; antenna; arrestin; Drosophila; electroantennogram; olfaction

Results 1-5 (5)