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Search Results: 1 - 10 of 200396 matches for " Jonathan D. Bohbot "
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Insect Repellents: Modulators of Mosquito Odorant Receptor Activity
Jonathan D. Bohbot,Joseph C. Dickens
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0012138
Abstract: DEET, 2-undecanone (2-U), IR3535 and Picaridin are widely used as insect repellents to prevent interactions between humans and many arthropods including mosquitoes. Their molecular action has only recently been studied, yielding seemingly contradictory theories including odorant-dependent inhibitory and odorant-independent excitatory activities on insect olfactory sensory neurons (OSNs) and odorant receptor proteins (ORs).
Characterization of an Enantioselective Odorant Receptor in the Yellow Fever Mosquito Aedes aegypti
Jonathan D. Bohbot, Joseph C. Dickens
PLOS ONE , 2009, DOI: 10.1371/journal.pone.0007032
Abstract: Enantiomers differ only in the left or right handedness (chirality) of their orientations and exhibit identical chemical and physical properties. In chemical communication systems, enantiomers can be differentially active at the physiological and behavioral levels. Only recently were enantioselective odorant receptors demonstrated in mammals while their existence in insects has remained hypothetical. Using the two-microelectrode voltage clamp of Xenopus oocytes, we show that the yellow fever mosquito, Aedes aegypti, odorant receptor 8 (AaOR8) acts as a chiral selective receptor for the (R)-(—)-enantiomer of 1-octen-3-ol, which in the presence of other kairomones is an attractant used by blood-sucking insects to locate their hosts. In addition to steric constraints, chain length and degree of unsaturation play important roles in this recognition process. This is the first characterization of an enantioselective odorant receptor in insects and the results demonstrate that an OR alone, without helper proteins, can account for chiral specificity exhibited by olfactory sensory neurons (OSNs).
Selectivity of odorant receptors in insects
Jonathan D. Bohbot,Joseph C. Dickens
Frontiers in Cellular Neuroscience , 2012, DOI: 10.3389/fncel.2012.00029
Abstract: Insect olfactory receptors (ORs) detect chemicals, shape neuronal physiology, and regulate behavior. Although ORs have been categorized as “generalists” and “specialists” based on their ligand spectrum, both electrophysiological studies and recent pharmacological investigations show that ORs specifically recognize non-pheromonal compounds, and that our understanding of odorant-selectivity mirrors our knowledge of insect chemical ecology. As we are progressively becoming aware that ORs are activated through a variety of mechanisms, the molecular basis of odorant-selectivity and the corollary notion of broad-tuning need to be re-examined from a pharmacological and evolutionary perspective.
Distinct Olfactory Signaling Mechanisms in the Malaria Vector Mosquito Anopheles gambiae
Chao Liu,R. Jason Pitts,Jonathan D. Bohbot,Patrick L. Jones,Guirong Wang,Laurence J. Zwiebel
PLOS Biology , 2012, DOI: 10.1371/journal.pbio.1000467
Abstract: Anopheles gambiae is the principal Afrotropical vector for human malaria, in which olfaction mediates a wide range of both adult and larval behaviors. Indeed, mosquitoes depend on the ability to respond to chemical cues for feeding, host preference, and mate location/selection. Building upon previous work that has characterized a large family of An. gambiae odorant receptors (AgORs), we now use behavioral analyses and gene silencing to examine directly the role of AgORs, as well as a newly identified family of candidate chemosensory genes, the An. gambiae variant ionotropic receptors (AgIRs), in the larval olfactory system. Our results validate previous studies that directly implicate specific AgORs in behavioral responses to DEET as well as other odorants and reveal the existence of at least two distinct olfactory signaling pathways that are active in An. gambiae. One system depends directly on AgORs; the other is AgOR-independent and requires the expression and activity of AgIRs. In addition to clarifying the mechanistic basis for olfaction in this system, these advances may ultimately enhance the development of vector control strategies, targeting olfactory pathways in mosquitoes to reduce the catastrophic effects of malaria and other mosquito-borne diseases.
Distinct Olfactory Signaling Mechanisms in the Malaria Vector Mosquito Anopheles gambiae
Chao Liu equal contributor,R. Jason Pitts equal contributor,Jonathan D. Bohbot,Patrick L. Jones,Guirong Wang,Laurence J. Zwiebel
PLOS Biology , 2010, DOI: 10.1371/journal.pbio.1000467
Abstract: Anopheles gambiae is the principal Afrotropical vector for human malaria, in which olfaction mediates a wide range of both adult and larval behaviors. Indeed, mosquitoes depend on the ability to respond to chemical cues for feeding, host preference, and mate location/selection. Building upon previous work that has characterized a large family of An. gambiae odorant receptors (AgORs), we now use behavioral analyses and gene silencing to examine directly the role of AgORs, as well as a newly identified family of candidate chemosensory genes, the An. gambiae variant ionotropic receptors (AgIRs), in the larval olfactory system. Our results validate previous studies that directly implicate specific AgORs in behavioral responses to DEET as well as other odorants and reveal the existence of at least two distinct olfactory signaling pathways that are active in An. gambiae. One system depends directly on AgORs; the other is AgOR-independent and requires the expression and activity of AgIRs. In addition to clarifying the mechanistic basis for olfaction in this system, these advances may ultimately enhance the development of vector control strategies, targeting olfactory pathways in mosquitoes to reduce the catastrophic effects of malaria and other mosquito-borne diseases.
Spatial navigational strategies correlate with gray matter in the hippocampus of healthy older adults tested in a virtual maze
Kyoko Konishi,Véronique D. Bohbot
Frontiers in Aging Neuroscience , 2013, DOI: 10.3389/fnagi.2013.00001
Abstract: Healthy young adults use different strategies when navigating in a virtual maze. Spatial strategies involve using environmental landmarks while response strategies involve executing a series of movements from specific stimuli. Neuroimaging studies previously confirmed that people who use spatial strategies show increased activity and gray matter in the hippocampus, while those who use response strategies show increased activity and gray matter in caudate nucleus (Iaria et al., 2003; Bohbot et al., 2007). A growing number of studies report that cognitive decline that occurs with normal aging is correlated with a decrease in volume of the hippocampus. Here, we used voxel-based morphometry (VBM) to examine whether spatial strategies in aging are correlated with greater gray matter in the hippocampus, as found in our previous study with healthy young participants. Forty-five healthy older adults were tested on a virtual navigation task that allows spatial and response strategies. All participants learn the task to criterion after which a special “probe” trial that assesses spatial and response strategies is given. Results show that spontaneous spatial memory strategies, and not performance on the navigation task, positively correlate with gray matter in the hippocampus. Since numerous studies have shown that a decrease in the volume of the hippocampus correlates with cognitive deficits during normal aging and increases the risks of ensuing dementia, the current results suggest that older people who use their spatial memory strategies in their everyday lives may have increased gray matter in the hippocampus and enhance their probability of healthy and successful aging.
Semantic Elaboration in Auditory and Visual Spatial Memory
Meghan Taevs,Robert J. Zatorre,Véronique D. Bohbot
Frontiers in Psychology , 2010, DOI: 10.3389/fpsyg.2010.00228
Abstract: The aim of this study was to investigate the hypothesis that semantic information facilitates auditory and visual spatial learning and memory. An auditory spatial task was administered, whereby healthy participants were placed in the center of a semi-circle that contained an array of speakers where the locations of nameable and non-nameable sounds were learned. In the visual spatial task, locations of pictures of abstract art intermixed with nameable objects were learned by presenting these items in specific locations on a computer screen. Participants took part in both the auditory and visual spatial tasks, which were counterbalanced for order and were learned at the same rate. Results showed that learning and memory for the spatial locations of nameable sounds and pictures was significantly better than for non-nameable stimuli. Interestingly, there was a cross-modal learning effect such that the auditory task facilitated learning of the visual task and vice versa. In conclusion, our results support the hypotheses that the semantic representation of items, as well as the presentation of items in different modalities, facilitate spatial learning and memory.
Sensory Cell Proliferation within the Olfactory Epithelium of Developing Adult Manduca sexta (Lepidoptera)
Marie-dominique Franco, Jonathan Bohbot, Kenny Fernandez, Jayd Hanna, James Poppy, Richard Vogt
PLOS ONE , 2007, DOI: 10.1371/journal.pone.0000215
Abstract: Background Insects detect a multitude of odors using a broad array of phenotypically distinct olfactory organs referred to as olfactory sensilla. Each sensillum contains one to several sensory neurons and at least three support cells; these cells arise from mitotic activities from one or a small group of defined precursor cells. Sensilla phenotypes are defined by distinct morphologies, and specificities to specific odors; these are the consequence of developmental programs expressed by associated neurons and support cells, and by selection and expression of subpopulations of olfactory genes encoding such proteins as odor receptors, odorant binding proteins, and odor degrading enzymes. Methodology/Principal Findings We are investigating development of the olfactory epithelium of adult M. sexta, identifying events which might establish sensilla phenotypes. In the present study, antennal tissue was examined during the first three days of an 18 day development, a period when sensory mitotic activity was previously reported to occur. Each antenna develops as a cylinder with an outward facing sensory epithelium divided into approximately 80 repeat units or annuli. Mitotic proliferation of sensory cells initiated about 20–24 hrs after pupation (a.p.), in pre-existing zones of high density cells lining the proximal and distal borders of each annulus. These high density zones were observed as early as two hr. a.p., and expanded with mitotic activity to fill the mid-annular regions by about 72 hrs a.p. Mitotic activity initiated at a low rate, increasing dramatically after 40–48 hrs a.p.; this activity was enhanced by ecdysteroids, but did not occur in animals entering pupal diapause (which is also ecdysteroid sensitive). Conclusions/Significance Sensory proliferation initiates in narrow zones along the proximal and distal borders of each annulus; these zones rapidly expand to fill the mid-annular regions. These zones exist prior to any mitotic activity as regions of high density cells which form either at or prior to pupation. Mitotic sensitivity to ecdysteroids may be a regulatory mechanism coordinating olfactory development with the developmental choice of diapause entry.
Virtual navigation strategies from childhood to senescence: evidence for changes across the life span
Veronique D. Bohbot,Sam McKenzie,Kyoko Konishi,Vanessa Kurdi,Russel Schachar,Philippe Robaey
Frontiers in Aging Neuroscience , 2012, DOI: 10.3389/fnagi.2012.00028
Abstract: This study sought to investigate navigational strategies across the life span, by testing 8-years old children to 80-years old healthy older adults on the 4 on 8 virtual maze (4/8VM). The 4/8VM was previously developed to assess spontaneous navigational strategies, i.e., hippocampal-dependent spatial strategies (navigation by memorizing relationships between landmarks) versus caudate nucleus-dependent response strategies (memorizing a series of left and right turns from a given starting position). With the 4/8VM, we previously demonstrated greater fMRI activity and gray matter in the hippocampus of spatial learners relative to response learners. A sample of 599 healthy participants was tested in the current study. Results showed that 84.4% of children, 46.3% of young adults, and 39.3% of older adults spontaneously used spatial strategies (p < 0.0001). Our results suggest that while children predominantly use spatial strategies, the proportion of participants using spatial strategies decreases across the life span, in favor of response strategies. Factors promoting response strategies include repetition, reward and stress. Since response strategies can result from successful repetition of a behavioral pattern, we propose that the increase in response strategies is a biological adaptive mechanism that allows for the automatization of behavior such as walking in order to free up hippocampal-dependent resources. However, the down-side of this shift from spatial to response strategies occurs if people stop building novel relationships, which occurs with repetition and routine, and thereby stop stimulating their hippocampus. Reduced fMRI activity and gray matter in the hippocampus were shown to correlate with cognitive deficits in normal aging. Therefore, these results have important implications regarding factors involved in healthy and successful aging.
The Summation of One Class of Infinite Series  [PDF]
Jonathan D. Weiss
Applied Mathematics (AM) , 2014, DOI: 10.4236/am.2014.517269
Abstract: This paper presents closed-form expressions for the series, \"\", where the sum is from n = 1 to n = ∞. These expressions were obtained by recasting the series in a different form, followed by the use of certain relationships involving the elliptical nome. Among the values of x for which these expressions can be obtained are of the form: \"\" and \"\", where l is an integer between ∞ and ∞. The values of λ include 1,\"\",\"\"and 3. Examples of closed-form expressions obtained in this manner are first presented for \"\", \"\", \"\", and \"\". Additional examples are then presented for \"\", \"\", \"\", and \"\". This undertaking was prompted by the author’s work on an electrostatics boundary-value problem related to the van der Pauw measurement technique of electrical resistivity. The presence of this series for x = \"\" in the solution of that problem and its absence from any compendium of infinite series that he consulted led to this work.
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