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1.  Organization and function of Drosophila odorant binding proteins 
eLife  null;5:e20242.
Odorant binding proteins (Obps) are remarkable in their number, diversity, and abundance, yet their role in olfactory coding remains unclear. They are widely believed to be required for transporting hydrophobic odorants through an aqueous lymph to odorant receptors. We construct a map of the Drosophila antenna, in which the abundant Obps are mapped to olfactory sensilla with defined functions. The results lay a foundation for an incisive analysis of Obp function. The map identifies a sensillum type that contains a single abundant Obp, Obp28a. Surprisingly, deletion of the sole abundant Obp in these sensilla does not reduce the magnitude of their olfactory responses. The results suggest that this Obp is not required for odorant transport and that this sensillum does not require an abundant Obp. The results further suggest a novel role for this Obp in buffering changes in the odor environment, perhaps providing a molecular form of gain control.
eLife digest
Insects use their sense of smell to find mates, to find food and – in the case of insects that transmit diseases such as malaria and Zika – to find us. If we can understand how insect scent detection works at the molecular and cellular level, we may be able to devise new ways of manipulating the insects’ sense of smell and prevent them from finding us.
Insects contain a family of proteins called odorant binding proteins that are intriguing in several ways. They are numerous (there are 52 kinds in the fruit fly Drosophila), they are diverse and some are made in remarkably large amounts in the antennae. Fine hair-like structures known as olfactory sensilla protrude from the surface of the antennae. Odorant binding proteins are widely believed to carry odorant molecules through the fluid inside the sensilla to olfactory neurons, which then send signals that trigger the insect’s response to the scent.
Larter et al. have now mapped the most abundant odorant binding proteins to the various olfactory sensilla of Drosophila. This revealed that a type of sensillum known as ab8 contained only one abundant odorant binding protein, called Obp28a. Unexpectedly, Larter et al. found that ab8 sensilla that are deprived of this protein respond strongly to odorant molecules. This result suggests that Obp28a is not required to transport odorants to the neurons in ab8; indeed, it appears that these neurons do not require an abundant odorant binding protein in order to respond to a scent. Instead, Obp28a helps to moderate the effects of sudden changes in the level of an odorant in the environment, so that concentrated odors do not trigger too large a response from the olfactory neurons.
The details of the role that Obp28a plays in olfactory sensilla remain to be investigated in future studies, and the map created by Larter et al. also lays a foundation for studying the roles of other odorant binding proteins. The discovery that Obp28a is not needed to transport odorant molecules also raises questions about how insects are able to detect smells. Many odorant molecules repel water, so how do these molecules travel through the fluid in the sensilla if odorant binding proteins are not needed to transport them?
PMCID: PMC5127637  PMID: 27845621
Drosophila; olfaction; odorants; odorant binding protein; D. melanogaster
2.  Drosophila chemoreceptors: A molecular interface between the chemical world and the brain 
Trends in genetics : TIG  2015;31(12):683-695.
Chemoreception is essential for survival. Feeding, mating, and avoidance of predators depend on detection of sensory cues. Drosophila contains diverse families of chemoreceptors that detect odors, tastants, pheromones, and noxious stimuli, including receptors of the Or, Gr, IR, Ppk, and Trp families. We consider recent progress in understanding chemoreception in the fly, including the identification of new receptors, the discovery of novel biological functions for receptors, and the localization of receptors in unexpected places. We discuss major unsolved problems and suggest areas that may be particularly ripe for future discoveries, including the roles of these receptors in driving the circuits and behaviors that are essential to the survival and reproduction of the animal.
PMCID: PMC4674303  PMID: 26477743
Odor receptor (Or); Gustatory receptor (Gr); Ionotropic glutamate receptor (IR); Olfactory Receptor Neuron (ORN); Olfaction; Taste
3.  Bitter taste receptors confer diverse functions to neurons 
eLife  null;5:e11181.
Bitter compounds elicit an aversive response. In Drosophila, bitter-sensitive taste neurons coexpress many members of the Gr family of taste receptors. However, the molecular logic of bitter signaling is unknown. We used an in vivo expression approach to analyze the logic of bitter taste signaling. Ectopic or overexpression of bitter Grs increased endogenous responses or conferred novel responses. Surprisingly, expression of Grs also suppressed many endogenous bitter responses. Conversely, deletion of an endogenous Gr led to novel responses. Expression of individual Grs conferred strikingly different effects in different neurons. The results support a model in which bitter Grs interact, exhibiting competition, inhibition, or activation. The results have broad implications for the problem of how taste systems evolve to detect new environmental dangers.
eLife digest
Insects and other animals use their sense of taste to tell if their food is safe to eat. Plant toxins, for example, often have a bitter flavor that animals can detect and avoid. Fruit flies have many bitter-sensitive nerve cells, but it is not known how the receptors on these nerve cells signal the detection of bitter-flavored compounds.
Delventhal and Carlson have now used fruit flies to investigate how taste receptors of the so-called Gustatory receptor family detect bitter flavors. The experimental approach involved genetically modifying four different types of nerve cells that sense bitter compounds so that they produced higher levels of particular taste receptors than normal. Then, the flies were exposed to a range of bitter compounds while the electrical activity of each cell was measured.
The analysis involved about 600 combinations of receptors, nerve cells and compounds. In some bitter-sensing nerve cells, increasing the number of taste receptors increased the cell’s responsiveness to bitter compounds. However, in other nerve cells, similar modifications suppressed an existing response or resulted in a new response.
Delventhal and Carlson propose that these results suggest the specific response of a bitter-sensing nerve cell depends on the interactions between its different taste receptors. Furthermore, the ability of receptors to compete, inhibit or activate each other in different ways could have implications for evolution. For example, such flexible interactions might allow a taste system to evolve new, enhanced or diminished responses to new food sources and tastes in a changing environment. It now remains to be investigated how such receptor interactions take place at a molecular level.
PMCID: PMC4764594  PMID: 26880560
taste receptors; electrophysiology; sensory systems; taste; D. melanogaster
4.  Reverse-correlation analysis of navigation dynamics in Drosophila larva using optogenetics 
eLife  null;4:e06225.
Neural circuits for behavior transform sensory inputs into motor outputs in patterns with strategic value. Determining how neurons along a sensorimotor circuit contribute to this transformation is central to understanding behavior. To do this, a quantitative framework to describe behavioral dynamics is needed. In this study, we built a high-throughput optogenetic system for Drosophila larva to quantify the sensorimotor transformations underlying navigational behavior. We express CsChrimson, a red-shifted variant of channelrhodopsin, in specific chemosensory neurons and expose large numbers of freely moving animals to random optogenetic activation patterns. We quantify their behavioral responses and use reverse-correlation analysis to uncover the linear and static nonlinear components of navigation dynamics as functions of optogenetic activation patterns of specific sensory neurons. We find that linear–nonlinear models accurately predict navigational decision-making for different optogenetic activation waveforms. We use our method to establish the valence and dynamics of navigation driven by optogenetic activation of different combinations of bitter-sensing gustatory neurons. Our method captures the dynamics of optogenetically induced behavior in compact, quantitative transformations that can be used to characterize circuits for sensorimotor processing and their contribution to navigational decision making.
eLife digest
Living organisms can sense their surroundings and respond in appropriate ways. For example, animals will often move towards the smell of food or away from potential threats, such as predators. However, it is not fully understood how an animal's nervous system is setup to allow sensory information to control how the animal navigates its environment.
Optogenetics is a technique that allows neuroscientists to control the activities of individual nerve cells in freely moving animals, simply by shining light on to them. Here, Hernandez-Nunez et al. have used optogenetics in fruit fly larvae to activate nerve cells that normally respond to smells and tastes, while the larvae's movements were tracked. Fruit fly larvae were chosen because they have a simple, but well-studied, nervous system. These larvae also move in two distinct ways: ‘runs’, in which a larva moves forward; and ‘turns’, during which a larva sweeps its head back and forth until it selects the direction of a new run.
The data from these experiments were quantified using a specific type of statistical analysis called ‘reverse correlation’ and used to build mathematical models that predict navigational behavior. This analysis of the experiments allowed Hernandez-Nunez et al. to reveal how specific sensory nerve cells can contribute to pathways that control an animal's navigation—and an independent study by Gepner, Mihovilovic Skanata et al. revealed similar results.
The approach of using optogenetics in combination with quantitative analysis, as used in these two independent studies, is now opening the door to a more complete understanding of the connections between the activity of sensory nerve cells and perception and behavior.
PMCID: PMC4466337  PMID: 25942453
optogenetics; chemotaxis; olfaction; gustation; D. melanogaster
5.  A map of taste neuron projections in the Drosophila CNS 
Journal of biosciences  2014;39(4):565-574.
We provide a map of the projections of taste neurons in the CNS of Drosophila. Using a collection of 67 GAL4 drivers representing the entire repertoire of Gr taste receptors, we systematically map the projections of neurons expressing these drivers in the thoracico-abdominal ganglion and the suboesophageal ganglion (SOG). We define 9 categories of projections in the thoracico-abdominal ganglia and 10 categories in the SOG. The projection patterns are modular, and can be interpreted as combinations of discrete pattern elements. The elements can be interpreted in terms of the taste organ from which the projections originate, the structures from which they originate, and the quality of taste information that they represent. The extensive diversity in projection patterns provides an anatomical basis for functional diversity in responses elicited by different taste stimuli.
PMCID: PMC4240268  PMID: 25116611
Drosophila; taste; taste receptors
6.  The Drosophila IR20a clade of Ionotropic Receptors are candidate taste and pheromone receptors 
Neuron  2014;83(4):850-865.
Insects use taste to evaluate food, hosts, and mates. Drosophila has many “orphan” taste neurons that express no known taste receptors. The Ionotropic Receptor (IR) superfamily is best known for its role in olfaction, but virtually nothing is known about a clade of ~35 members, the IR20a clade. Here, a comprehensive analysis of this clade reveals expression in all taste organs of the fly. Some members are expressed in orphan taste neurons, whereas others are coexpressed with bitter- or sugar-sensing Gustatory receptor (Gr) genes. Analysis of the closely related IR52c and IR52d genes reveals signatures of adaptive evolution, roles in male mating behavior, and sexually dimorphic expression in neurons of the male foreleg, which contacts females during courtship. These neurons are activated by conspecific females and contact a neural circuit for sexual behavior. Together, these results greatly expand the repertoire of candidate taste and pheromone receptors in the fly.
PMCID: PMC4141888  PMID: 25123314
7.  The Molecular and Cellular Basis of Taste Coding in the Legs of Drosophila 
The Journal of Neuroscience  2014;34(21):7148-7164.
To understand the principles of taste coding, it is necessary to understand the functional organization of the taste organs. Although the labellum of the Drosophila melanogaster head has been described in detail, the tarsal segments of the legs, which collectively contain more taste sensilla than the labellum, have received much less attention. We performed a systematic anatomical, physiological, and molecular analysis of the tarsal sensilla of Drosophila. We construct an anatomical map of all five tarsal segments of each female leg. The taste sensilla of the female foreleg are systematically tested with a panel of 40 diverse compounds, yielding a response matrix of ∼500 sensillum–tastant combinations. Six types of sensilla are characterized. One type was tuned remarkably broadly: it responded to 19 of 27 bitter compounds tested, as well as sugars; another type responded to neither. The midleg is similar but distinct from the foreleg. The response specificities of the tarsal sensilla differ from those of the labellum, as do n-dimensional taste spaces constructed for each organ, enhancing the capacity of the fly to encode and respond to gustatory information. We examined the expression patterns of all 68 gustatory receptors (Grs). A total of 28 Gr–GAL4 drivers are expressed in the legs. We constructed a receptor-to-sensillum map of the legs and a receptor-to-neuron map. Fourteen Gr–GAL4 drivers are expressed uniquely in the bitter-sensing neuron of the sensillum that is tuned exceptionally broadly. Integration of the molecular and physiological maps provides insight into the underlying basis of taste coding.
PMCID: PMC4028494  PMID: 24849350
Drosophila; Gr; gustatory receptor; legs; physiology; taste
8.  Molecular determinants of odorant receptor function in insects 
Journal of biosciences  2014;39(4):555-563.
The olfactory system of Drosophila melanogaster provides a powerful model to study molecular and cellular mechanisms underlying function of a sensory system. In the 1970s Siddiqi and colleagues pioneered the application of genetics to olfactory research and isolated several mutant Drosophila with odorant-specific defects in olfactory behaviour, suggesting that odorants are detected differentially by the olfactory system. Since then basic principles of olfactory system function and development have emerged using Drosophila as a model. Nearly four decades later we can add computational methods to further our understanding of how specific odorants are detected by receptors. Using a comparative approach we identify two categories of short amino acid sequence motifs: ones that are conserved family-wide predominantly in the C-terminal half of most receptors, and ones that are present in receptors that detect a specific odorant, 4-methylphenol, found predominantly in the N-terminal half. The odorant-specific sequence motifs are predictors of phenol detection in Anopheles gambiae and other insects, suggesting they are likely to participate in odorant binding. Conversely, the family-wide motifs are expected to participate in shared functions across all receptors and a mutation in the most conserved motif leads to a reduction in odor response. These findings lay a foundation for investigating functional domains within odorant receptors that can lead to a molecular understanding of odor detection.
PMCID: PMC4385708  PMID: 25116610
Drosophila; motifs; odor receptor; olfaction
9.  Malaria Parasites Produce Volatile Mosquito Attractants 
mBio  2015;6(2):e00235-15.
The malaria parasite Plasmodium falciparum contains a nonphotosynthetic plastid organelle that possesses plant-like metabolic pathways. Plants use the plastidial isoprenoid biosynthesis pathway to produce volatile odorants, known as terpenes. In this work, we describe the volatile chemical profile of cultured malaria parasites. Among the identified compounds are several plant-like terpenes and terpene derivatives, including known mosquito attractants. We establish the molecular identity of the odorant receptors of the malaria mosquito vector Anopheles gambiae, which responds to these compounds. The malaria parasite produces volatile signals that are recognized by mosquitoes and may thereby mediate host attraction and facilitate transmission.
Malaria is a key global health concern. Mosquitoes that transmit malaria are more attracted to malaria parasite-infected mammalian hosts. These studies aimed to understand the chemical signals produced by malaria parasites; such an understanding may lead to new transmission-blocking strategies or noninvasive malaria diagnostics.
PMCID: PMC4453533  PMID: 25805727
10.  An RNA-Seq Screen of the Drosophila Antenna Identifies a Transporter Necessary for Ammonia Detection 
PLoS Genetics  2014;10(11):e1004810.
Many insect vectors of disease detect their hosts through olfactory cues, and thus it is of great interest to understand better how odors are encoded. However, little is known about the molecular underpinnings that support the unique function of coeloconic sensilla, an ancient and conserved class of sensilla that detect amines and acids, including components of human odor that are cues for many insect vectors. Here, we generate antennal transcriptome databases both for wild type Drosophila and for a mutant that lacks coeloconic sensilla. We use these resources to identify genes whose expression is highly enriched in coeloconic sensilla, including many genes not previously implicated in olfaction. Among them, we identify an ammonium transporter gene that is essential for ammonia responses in a class of coeloconic olfactory receptor neurons (ORNs), but is not required for responses to other odorants. Surprisingly, the transporter is not expressed in ORNs, but rather in neighboring auxiliary cells. Thus, our data reveal an unexpected non-cell autonomous role for a component that is essential to the olfactory response to ammonia. The defective response observed in a Drosophila mutant of this gene is rescued by its Anopheles ortholog, and orthologs are found in virtually all insect species examined, suggesting that its role is conserved. Taken together, our results provide a quantitative analysis of gene expression in the primary olfactory organ of Drosophila, identify molecular components of an ancient class of olfactory sensilla, and reveal that auxiliary cells, and not simply ORNs, play an essential role in the coding of an odor that is a critical host cue for many insect vectors of human disease.
Author Summary
Olfaction underlies the attraction of insect pests and vectors of disease to their plant and human hosts. In the genetic model insect Drosophila, the neuronal basis of odor coding has been extensively analyzed in the antenna, its major olfactory organ, but the molecular basis of odor coding has not. Additionally, there has been little analysis of any olfactory cells other than neurons. We have undertaken a comprehensive and quantitative analysis of gene expression in the Drosophila antenna. This analysis revealed a surprisingly broad dynamic range of odor receptor and odor binding protein expression, and unexpected expression of taste receptor genes. Further analysis identified 250 genes that are expressed at reduced levels in a mutant lacking an evolutionarily ancient class of sensilla, antennal hairs housing neurons that respond to human odors. One of these genes, a transporter, is expressed in non-neuronal cells but is essential to the response of a neuron to ammonia, a key cue for insect vectors of disease. A mutation in this transporter can be rescued by its mosquito homolog. While many studies of sensory coding consider the neural circuit in isolation, our analysis reveals an essential role for an auxiliary cell.
PMCID: PMC4238959  PMID: 25412082
11.  Interspecies Sex and Taste 
Cell  2013;154(1):20-21.
Different species of fruit flies share habitats but are believed to mate with each other only rarely. In this issue, Fan et al. show that interspecies mating is inhibited by the taste receptor Gr32a (Gustatory receptor 32a) and a neural circuit in which it functions.
PMCID: PMC3756821  PMID: 23827670
12.  Similar Odorants Elicit Different Behavioral and Physiological Responses, Some Supersustained 
An intriguing question in the field of olfaction is how animals distinguish among structurally similar odorants. We systematically analyzed olfactory responses elicited by a panel of 25 pyrazines. We found that structurally similar pyrazines elicit a wide range of behavioral responses from Drosophila larvae. Each pyrazine was tested against all functional receptors of the larval Odor receptor (Or) repertoire, yielding 525 odorant–receptor combinations. Different pyrazines vary markedly in the responses they elicit from the Or repertoire, with most strong responses deriving from two receptors, Or33b and Or59a. Surprisingly, 2-ethylpyrazine and 2-methylpyrazine, which elicit strikingly similar physiological responses across the receptor repertoire, elicit dramatically different behavioral responses. A small fraction of odorant-receptor combinations elicit remarkably long responses. These responses, which we term “supersustained” responses, are receptor specific and odorant specific, and can last for minutes. Such supersustained responses may prevent olfactory neurons from reporting contemporaneous information about the local odor environment. Odors that elicit such responses could provide a novel means of controlling insect pests and vectors of human disease by impairing the location of human hosts, food sources, and mates.
PMCID: PMC3116233  PMID: 21613503
13.  Intensity invariant dynamics and odor-specific latencies in olfactory receptor neuron response 
Odors elicit spatio-temporal patterns of activity in the brain. Spatial patterns arise from the specificity of the interaction between odorants and odorant receptors expressed in different olfactory receptor neurons (ORNs). But the origin of temporal patterns of activity and their role in odor coding remain unclear. We investigate how physiological aspects of ORN response and physical aspects of odor stimuli give rise to diverse responses in Drosophila ORNs. We show that odor stimuli have intrinsic dynamics that depend on odor type and strongly affect ORN response. Using linear-nonlinear modeling to remove the contribution of the stimulus dynamics from the ORN dynamics we study the physiological properties of the response to different odorants and concentrations. For several odorants and receptor types the ORN response dynamics normalized by the peak response are independent of stimulus intensity for a large portion of the neuron’s dynamic range. Adaptation to a background odor changes the gain and dynamic range of the response but does not affect normalized response dynamics. Stimulating ORNs with various odorants reveals significant odor-dependent delays in the ORN response functions. These differences however can be dominated by differences in stimulus dynamics. In one case the response of one ORN to two odorants is predicted solely from measurements of the odor signals. Within a large portion of their dynamic range ORNs can capture information about stimulus dynamics independently from intensity while introducing odor-dependent delays. How insects might use odor-specific stimulus dynamics and ORN dynamics in discrimination and navigation tasks remains an open question.
PMCID: PMC3678969  PMID: 23575828
14.  Distinct functions of acj6 splice forms in odor receptor gene choice 
Individual olfactory receptor neurons (ORNs) selectively express one or a small number of odor receptors from among a large receptor repertoire. The expression of an odor receptor dictates the odor response spectrum of the ORN. The process of receptor gene choice relies in part on a combinatorial code of transcription factors. In Drosophila, the POU domain transcription factor Acj6 is one element of the transcription factor code. In acj6 null mutants, many ORNs do not express an appropriate odor receptor gene and thus are not correctly specified. We find that acj6 is alternatively spliced to yield many structurally distinct transcripts in the olfactory organs. We generate flies that express single splice forms of acj6 in an acj6− background. We find that different splice forms are functionally distinct; they differ in their abilities to specify ORN identities. Some individual splice forms can fully rescue the specification of some ORNs. Individual splice forms can function both positively and negatively in receptor gene regulation. ORNs differ in their requirements for splice forms; some are not fully rescued by any single splice form tested, suggesting that some ORNs may require the combinatorial action of multiple splice forms. Late expression of some acj6 splice forms is sufficient to rescue some ORN classes, consistent with a direct role for Acj6 isoforms in receptor gene expression. The results indicate that alternative splicing may add another level of richness to the regulatory code that underlies the process of odor receptor gene choice.
PMCID: PMC2858447  PMID: 20371823
olfaction; Drosophila; Acj6; POU-domain; odor receptor; splicing
15.  Role of G-proteins in odor-sensing and CO2–sensing neurons in Drosophila 
A central question in insect chemoreception is whether signaling occurs via G-proteins. Two families of seven-transmembrane-domain chemoreceptors, the Or and Gr receptor families, have been identified in Drosophila (Clyne et al., 1999; Vosshall et al., 1999; Clyne et al., 2000). Or receptors mediate odor responses while two Gr receptors, Gr21a and Gr63a, mediate CO2 response (Hallem et al., 2004; Jones et al., 2007; Kwon et al., 2007). Using single-sensillum recordings, we systematically investigate the role of Gα proteins in vivo, initially with RNAi constructs, competitive peptides, and constitutively active Gα proteins. The results do not support a role for Gα proteins in odor sensitivity. In parallel experiments, manipulations of Gαq, but not other Gα proteins, affected CO2 response. Transient, conditional, and ectopic expression analyses consistently supported a role for Gαq in the response of CO2-sensing neurons, but not odor-sensing neurons. Genetic mosaic analysis confirmed that odor responses are normal in the absence of Gαq. Gγ30A is also required for normal CO2 response. The simplest interpretation of these results is that Gαq and Gγ30A play a role in the response of CO2-sensing neurons, but are not required for Or-mediated odor signaling.
PMCID: PMC2858456  PMID: 20357107
Olfactory; Drosophila; Transduction; Receptor; GPCR; signal transduction
16.  Non-synaptic inhibition between grouped neurons in an olfactory circuit 
Nature  2012;492(7427):66-71.
Diverse sensory organs, including mammalian taste buds and insect chemosensory sensilla, show a striking compartmentalization of receptor cells. However, the functional impact of this organization remains unclear. Here we show that compartmentalized Drosophila olfactory receptor neurons (ORNs) communicate with each other directly. The sustained response of one ORN is inhibited by the transient activation of a neighboring ORN. Mechanistically, such lateral inhibition does not depend on synapses and is likely mediated by ephaptic coupling. Moreover, lateral inhibition in the periphery can modulate olfactory behavior. Together, the results show that integration of olfactory information can occur via lateral interactions between ORNs. Inhibition of a sustained response by a transient response may provide a means of encoding salience. Finally, a CO2-sensitive ORN in the malaria mosquito Anopheles can also be inhibited by excitation of an adjacent ORN, suggesting a broad occurrence of lateral inhibition in insects and possible applications in insect control.
PMCID: PMC3518700  PMID: 23172146
17.  Positive and negative regulation of odor receptor gene choice in Drosophila by Acj6 
Little is known about how individual olfactory receptor neurons (ORNs) select, from among many odor receptor genes, which genes to express. Acj6 (Abnormal chemosensory jump 6) is a POU-domain transcription factor essential for the specification of ORN identity and Or (odor receptor) gene expression in the Drosophila maxillary palp, one of the two adult olfactory organs. However, the mechanism by which Acj6 functions in this process has not been investigated. Here we systematically examine the role of Acj6 in the maxillary palp and in a major subset of antennal ORNs. We define an Acj6 binding site by a reiterative in vitro selection process. The site is found upstream of Or genes regulated by Acj6, and Acj6 binds to the site in Or promoters. Mutational analysis shows that the site is essential for Or regulation in vivo. Surprisingly, a novel ORN class in acj6 adults is found to arise from ectopic expression of a larval Or gene, which is repressed in wild-type via an Acj6 binding site. Thus Acj6 acts directly in the process of receptor gene choice; it plays a dual role, positive and negative, in the logic of the process, and acts in partitioning the larval and adult receptor repertoires.
PMCID: PMC2782464  PMID: 19828808
olfaction; Drosophila; Acj6; POU-domain; maxillary palp; antenna
18.  Controlling airborne cues to study small animal navigation 
Nature methods  2012;9(3):290-296.
Small animals like nematodes and insects analyze airborne chemical cues to infer the direction of favorable and noxious locations. In these animals, the study of navigational behavior evoked by airborne cues has been limited by the difficulty of precise stimulus control. We present a system that enables us to deliver gaseous stimuli in defined spatial and temporal patterns to freely moving small animals. We use this apparatus, in combination with machine vision algorithms, to assess and quantify navigational decision-making of Drosophila larvae in response to ethyl acetate (a volatile attractant) and carbon dioxide (a gaseous repellant).
PMCID: PMC3513333  PMID: 22245808
19.  Exploratory Analysis of Cerebral Oxygen Reserves during Sleep Onset in Old and Young Adults 
To explore differences in cerebral oxygen reserves during sleep in old and young adults
Descriptive cross-sectional study
General Clinical Research Center
Nine old (65–84yrs) and 10 young (21–39yrs) adults
Subjects were monitored during the first nightly sleep cycle using standard polysomnography, including measures of arterial oxyhemoglobin saturation (SaO2). Changes in regional cerebral oxyhemoglobin saturation (rcSO2) were used to estimate cerebral oxygen reserves. General linear models were used to test group differences in the change in SaO2 and rcSO2 during sleep.
Compared to young subjects, the old had reduced SaO2, both before sleep (baseline) (F(1,18)=5.1, p=.04) and when asleep (F(1,18)=5.14, p=.04). During sleep, half of the old and none of the young had SaO2 values below 95%. In addition, the old had more periods of oxygen desaturation (drops in SaO2≥4%) (X2=24.3, p=.01) and lower SaO2 levels during desaturation (F(1,18)=11.11, p<.01). Although baseline values were similar, rcSO2 decreased during sleep by 2.1% in the old (F(1,8)=3.8, p=.05) but increased by 2.1% during sleep in the young (F(1,9)=4.6, p=.04). When the old awakened from sleep, the rcSO2, but not the SaO2, returned to baseline; both returned to baseline in the young.
This exploratory analysis generates the hypothesis that lower SaO2, combined with declines in regional blood flow, contributes to the decline in cerebral oxygen reserves during sleep in the old. Further study will assess the effects of factors (e.g. medical conditions, subclinical disorders, and sleep architecture) that might account for these differences.
PMCID: PMC3377447  PMID: 18384588
Brain Hypoxia; Hypoxemia; Aging; Sleep; Oximetry
20.  Cerebrovascular Disease and Patterns of Cerebral Oxygenation during Sleep in Elders 
Biological Research for Nursing  2009;10(4):307-317.
The aim of this descriptive exploratory study was to describe patterns of cerebral oxygen reserves during sleep and their association with cerebrovascular risk factors in elders.
Participants--115 elders, age 70+ years--were monitored overnight using standard polysomnography. Measures included arterial oxyhemoglobin (SaO2) and regional measures of percent cerebral oxyhemoglobin saturation (rcSO2) via cerebral oximetry. Subjects were classified based on the magnitude of change in rcSO2 from resting baseline to the end of the first non-rapid-eye-movement (NREM) period. One way ANOVA and Chi-square were used to test group differences in SaO2 and the prevalence of cerebrovascular risk factors.
20 subjects (Group 1) experienced an increase in rcSO2 during sleep along with sleeping rcSO2 levels ≥ 55%; 95 subjects experienced a decline in rcSO2; 72 subjects (Group 2) had sleeping rcSO2 levels ≥ 55%; and 23 subjects had sleeping rcSO2 levels < 55% (Group 3). Although all three groups had equivalent declines in SaO2 levels during sleep, Group 3 had more cardiovascular comorbidity than Groups 1 and 2.
While SaO2 levels decline in most people during sleep, compensatory vascular responses to these drops in SaO2 are important for preventing rcSO2 from falling during sleep. Those entering sleep with lower baseline rcSO2 levels and those with greater declines in cerebral oxygenation during sleep may have greater cardiovascular burden and be at greater risk for stroke and other forms of disabling cerebrovascular disease.
PMCID: PMC3377477  PMID: 19144652
Aging; Sleep; Oxygenation; Cerebral; Arterial; Blood Flow; Instrumentation
21.  Tailoring Protocols to Successfully Recruit and Retain Elders in a Longitudinal Study of Sleep and Cognition 
Many studies attest to the challenges of recruiting and retaining older adults in longitudinal studies. This article presents the methods used by the Physiological Research to Improve Sleep and Memory Project to recruit and retain 115 adults (70+ years) in a 2-year study that involved yearly administrations of two neurocognitive test batteries and two nights of polysomnography. The paper describes strategies which are built on knowledge obtained from participant informants and the use of tailored, individualize protocols. Together, these strategies enabled participants to become vested in the research process and to fully participate in all aspects of the study.
PMCID: PMC3365503  PMID: 20077997
Research Subjects; Cognition; Sleep; Frail Elders; Prospective Studies
22.  Molecular and cellular organization of the taste system in the Drosophila larva 
We examine the molecular and cellular basis of taste perception in the Drosophila larva, through a comprehensive analysis of the expression patterns of all 68 Gustatory receptors (Grs). Gr-GAL4 lines representing each Gr are examined, and 39 show expression in taste organs of the larval head, including the terminal organ (TO), the dorsal organ (DO), and the pharyngeal organs. A receptor-to-neuron map is constructed. The map defines 10 neurons of the TO and DO, and it identifies 28 receptors that map to them. Each of these neurons expresses a unique subset of Gr-GAL4 drivers, except for two neurons that express the same complement. All of these neurons express at least two drivers, and one neuron expresses 17. Many of the receptors map to only one of these cells, but some map to as many as six. Conspicuously absent from the roster of Gr-GAL4 drivers expressed in larvae are those of the sugar receptor subfamily. Coexpression analysis suggests that most larval Grs act in bitter response, and that there are distinct bitter-sensing neurons. A comprehensive analysis of central projections confirms that sensory information collected from different regions, e.g. the tip of the head vs the pharynx, is processed in different regions of the suboesophageal ganglion (SOG), the primary taste center of the central nervous system. Taken together, the results provide an extensive view of the molecular and cellular organization of the larval taste system.
PMCID: PMC3225198  PMID: 22031876
23.  The Molecular and Cellular Basis of Bitter Taste in Drosophila 
Neuron  2011;69(2):258-272.
The extent of diversity among bitter-sensing neurons is a fundamental issue in the field of taste. Data are limited and conflicting as to whether bitter neurons are broadly tuned and uniform, resulting in indiscriminate avoidance of bitter stimuli, or diverse, allowing a more discerning evaluation of food sources. We provide a systematic analysis of how bitter taste is encoded by the major taste organ of the Drosophila head, the labellum. Each of 16 bitter compounds is tested physiologically against all 31 bitter neurons, revealing responses that are diverse in magnitude and dynamics. Four functional classes of bitter neurons are defined. Four corresponding classes are defined through expression analysis of all 68 Gr taste receptors. A receptor-to-neuron-to-tastant map is constructed. Misexpression of one receptor confers bitter responses as predicted by the map. These results reveal a degree of complexity that greatly expands the capacity of the system to encode bitter taste.
PMCID: PMC3033050  PMID: 21262465
24.  Cerebral Oxygenation in Wake and During Sleep and Its Relationship to Cognitive Function in Community-Dwelling Older Adults Without Sleep Disordered Breathing 
This descriptive cross-sectional study investigated the relationships between cerebral oxygen reserve and cognitive function in community-dwelling older adults.
Participants (72 women and 40 men) underwent standard polysomnography, including regional measures of percent oxyhemoglobin saturation (rcSO2) determined by cerebral oximetry. Two variables were used to calculate cerebral oxygen reserve: (a) awake rcSO2 (mean presleep rcSO2) and (b) the change in rcSO2 from before sleep to the end of the first non-rapid-eye movement cycle. General linear models, adjusted for the effects of education and occupation, tested differences in performance on standard tests of memory, attention, and speed of mental processing.
Awake rcSO2 values were normal (60%–79.9%) in 64 participants, marginal (50%–59.9%) in 41, and low (43%–49.9%) in 7. Participants with normal awake levels had higher cognitive function than those with low levels (p < .05). Changes in rcSO2 were greatest in participants with marginal awake rcSO2 values; among whom, those who increased rcSO2 during sleep (n = 17) had better memory function than the 24 who did not (p < .05).
Low awake rcSO2 values mark individuals with low cerebral oxygen reserves and generally lower cognitive function; marginal awake rcSO2 values that fall during sleep may indicate loss of cerebral oxygen reserve and an increased risk for cognitive decline. Further studies may clarify the significance of and mechanisms underlying individual differences in awake rcSO2 and the changes that occur in rcSO2 while asleep.
PMCID: PMC3011955  PMID: 21076087
Cerebral oxygenation; Sleep; Cognition
25.  The Influence of Literacy on Patient-Reported Experiences of Diabetes Self-Management Support 
Nursing research  2010;59(5):356-363.
Variability in disease-related outcomes may relate to how patients experience self-management support in clinical settings.
To identify factors associated with experiences of self-management support during primary care encounters.
A cross-sectional survey was conducted of 208 patients seen in a multidisciplinary diabetes program in an academic medicine clinic. Multiple regression analysis was used to test associations between patient-rated experiences of self-management support (Patient Assessment of Chronic Illness Care [PACIC]) and race, gender, insurance status, literacy, duration of diabetes, and intensity of care management.
The PACIC ratings decreased with age (r = −0.235, p = .001), were higher for women than for men (3.95 vs. 3.65, t = 2.612, p = .010), and were greater for those with more education (F = 3.927, p = .009) and greater literacy skills (t = 3.839, p < .001). The ratings did not vary between racial (t = −1.108, p = .269) or insurance (F = 1.045, p = .374) groups and were unaffected by duration of diabetes (r = 0.052, p = .466) and the intensity of care management (F = 1.028, p = .360). In multivariate models, literacy was the only variable contributing significantly to variation in self-management support ratings.
Even when considering the objective intensity of health services delivered, literacy was the sole variable contributing to differences in patient ratings of self-management support. Although conclusions are limited by the cross-sectional nature of this study, the results emphasize the need to consider literacy when developing and communicating treatment plans requiring self-management skills.
PMCID: PMC2946184  PMID: 20808193
diabetes mellitus; self-care; literacy

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