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Wragg, Rachel, Komuniecki, Richard, Harris, Gareth P., Hapiak, Vera, Summers, Philip, Korchnak, Amanda
[
International Worm Meeting,
2009]
Serotonin modulates many key behaviors in C. elegans, including the stimulation of aversive responses to dilute octanol mediated by the ASH sensory neurons (Harris et al., 2009, J. Neuroscience 29, 1446-1456). The serotonergic stimulation of ASH-mediated aversive responses requires the expression of SER-5 in the ASHs, but the site of SER-5 action is unclear. For example, SER-5 signaling may increase the release of glutamate and/or neuropeptides from the the ASHs. Indeed, the ASHs express multiple peptide encoding genes, including
nlp-3 and
nlp-15, and the peptides encoded by these genes have multiple effects on ASH signaling. For example,
nlp-3 null animals exhibit wild-type basal responses to dilute octanol, but do not increase aversive responses in the presence of food or 5-HT. In contrast,
nlp-15 null animals exhibit elevated basal responses to dilute octanol in the absence of either food or 5-HT and these elevated basal responses are not inhibited by octopamine. As predicted, animals overexpressing
nlp-15 respond only weakly to dilute octanol and exhibit dramatically reduced basal responses. Interestingly, in these
nlp-15 overexpressors, aversive responses can be stimulated to near wild-type levels by food or 5-HT. Together, these results suggest that
nlp-15 inhibits ASH signaling by a mechanism that may not directly involve NT release from the ASHs. These observations have been confirmed by the ASH rescue and RNAi knockdown of
nlp-15 and
nlp-3. In addition, we have identified a number of other genes encoding peptides and peptide receptors that are also involved in modulating various aspects of ASH mediated signaling, highlighting the complexity of peptidergic modulation. These studies are continuing with the goal of identifying the receptors and downstream signaling pathways mediating the differential effects of
nlp-3 and
nlp-15 on signaling in the ASH sensory neurons.
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[
International Worm Meeting,
2015]
Odor sensation, discrimination and preference are critical components of human behavior. The ability to recognize and discriminate between odors, and generate preference for individual scents is associated with many aspects of behavior. An array of neurological diseases share significant deficits in olfactory-based behavior at the level of odor processing, discrimination and plasticity. Using C. elegans, we have previously demonstrated that the worm can recognize and generate olfactory preference among foods, such as E. coli OP50 and PA14. We previously identified distinct but overlapping signaling pathways and neural circuits regulating olfactory sensation versus preference when comparing different foods. The pathways require canonical sensory transduction pathways and glutamate for olfactory recognition, and specific peptide pathways for preference. We have focused on the later pathway, which will allow us to understand not only how a preference is generated, but also how it can be modulated by experience. We have now identified distinct interneurons that mediate olfactory recognition versus preference. Furthermore, we have begun to examine the role of various C. elegans genes whose human homologs are associated with neurodegenerative diseases in regulating olfactory recognition and preference. We have found that the presenilin-encoding gene plays an important role in mediating sensori-motor response to complex olfactory cues. We are further dissecting the functional sites of presenilin in the neural circuits underlying food odor recognition and preference. Various neurological diseases disrupt cognitive functions, including learning and memory. Our study will potentially provide insights into the underlying mechanisms.
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Zhang, Xiaodong, Zhang, Yun, Ha, Heon-Ick, Shen, Yu, Donato, Alessandra, Harris, Gareth
[
International Worm Meeting,
2013]
Food is an essential environmental cue. Many organisms, including Caenorhabditis elegans, utilize chemosensory systems and locomotory strategies to sense food availability and to locate preferred food sources that are essential for survival. However, the signaling mechanisms underlying food-seeking decisions are not well understood. Previously, we have mapped an olfactory circuit required for animals to generate olfactory preference between two bacterial foods (Ha et al., 2010). Here, we characterize the molecular and cellular events that act in this neuronal network to regulate sensory-motor behavior during food odor preference. Using a combination of behavior, reverse genetics and physiological analysis, we show that both of the major olfactory sensory neurons, AWB and AWC, are required for food-odor preferences via sensory-motor control of locomotion. A canonical signaling pathway of Ga protein signaling, together with two guanylate cyclases and a cGMP-gated channel regulate behavioral responses to food odors. Further, the Ga protein signaling also regulates neuronal calcium response of AWB and AWC sensory neurons during food-odor perception. These food-odor evoked signals are transmitted from AWC via co-transmission of glutamate and neuropeptides and from AWB via neuropeptidergic signals and predicted downstream neuropeptide receptors. Furthermore, sensory dependent glutamate signaling requires a combinational function of the AMPA and Kainate-like glutamate receptor subunits to generate food odor preference. These mechanistic logics together with a previously mapped neural circuit provides a functional network that links sensory transduction, sensory signaling output and downstream receptor targets during the perception and processing of complex odors to generate the appropriate behavioral decision essential for survival.
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[
C.elegans Neuronal Development Meeting,
2008]
Serotonin (5-HT) modulates many key behaviors in Caenorhabditis elegans. For example, 5-HT increases aversive responses to dilute (30%) octanol, a process mediated primarily by the ASH sensory neurons (Chao et al., 2004, PNAS 101:15512). Previously, we demonstrated that at least three different 5-HT receptors were essential for serotonergic sensitization to dilute octanol, two G-protein coupled receptors, SER-1 and F16D3.7 and a 5-HT gated chloride channel, MOD-1. Based on neuron-specific rescues, the three receptors appeared to function at different levels within the ASH-mediated circuit initiating backward locomotion, F16D3.7 in the sensory neurons, MOD-1 in AIA/AIB interneurons and SER-1 in the RIA/ring motor neurons (ref to abstract). In the present study, we have identified the 5-HT receptors involved in another 5-HT stimulated ASH-mediated aversive response, nose touch. Although nose touch is mediated primarily by the ASH sensory neurons, two additional sensory neurons, FLP and OLQ are also involved. Interestingly, we also have identified three different 5-HT receptors in the food or 5-HT mediated sensitization of nose touch. As observed for sensitivity to dilute octanol, both F16D3.7 and SER-1 are involved. However, in contrast to dilute octanol, SER-4, but not MOD-1 is required for 5-HT dependent increases in aversive responses to nose touch. The Galphao coupled SER-4 is likely to inhibit neurotransmitter release, as is MOD-1, but the specific neurons involved remain to be identified. SER-4 does not appear to be expressed in AIA/AIB. Taken together, these results suggest that overlapping, but different serotonergic circuits modulate ASH mediated behavior, surprisingly each of the 5-HT receptors appear essential for sensitization; no partial responses were observed. These studies are continuing to identify the individual neurons involved through a combination of neuron-specific rescue and RNAi knockdown of individual receptors and signaling molecules, coupled to direct electrophysiological recording from individual neurons. This work is supported by NIH grant AI45147 to RWK
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[
International Worm Meeting,
2007]
Serotonin (5-HT) modulates a number of key behaviors in C. elegans, including pharyngeal pumping, egg-laying, locomotion, aversive learning and olfaction. For example, Chao et al., 2004 (PNAS, 101:15512) demonstrated that reversal in response to dilute octanol is mediated primarily by the ASH sensory neurons and, more importantly, that 5-HT or bacteria causes animals to reverse more rapidly. To date, four distinct C. elegans 5-HT receptors have been identified, three G-protein coupled receptors, SER-1, SER-4, SER-7 and a 5-HT gated Cl- channel, MOD-1. In the present study, we have examined the effects of 5-HT on sensitivity to dilute octanol in animals containing null alleles of each of these 5-HT receptors, either singly or in combination. Both
ser-1(
ok345) and mod-l
(ok103) null animals failed to respond to 5-HT in these assays and 5-HT dependent increases in octanol sensitivity could be restored in these strains by introducing either a full length
ser-1::gfp transgene with sequence coding for GFP inserted into the predicted SER-1 C-terminus that is expressed in 5 pairs of head neurons (Xiao et al., 2006, Dev. Biol. 298:379) or a full length mod-l transgene, respectively. Interestingly, mod-l
(ok103) null animals also could be rescued with a Podr-2(2b)::
mod-1 transgene that is expressed primarily in the AIB/AIZ primary interneurons. Since neither
ser-1 or mod-l appears to be expressed directly in the ASH, we examined the role of other putative, previously uncharacterized, 5-HT receptors on 5-HT dependent increases in octanol sensitivity by RNAi in an
rrf-3 sensitized background. Indeed, using this approach, we identified a third gene encoding a putative 5-HT receptor that is expressed in a number of sensory neurons, including the ASH, and is required for 5-HT dependent increases in octanol sensitivity. Taken together, these results suggest that at least three 5-HT receptors, located at distinct levels within the sensory/locomotory circuit, are essential for 5-HT dependent increases in octanol sensitivity.
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[
MicroPubl Biol,
2020]
An environment is often represented by numerous sensory cues. In order to better survive, an animal often needs to detect and process sensory cues simultaneously to make an appropriate behavioral decision. The Caenorhabditis elegans (C. elegans) genome encodes homologues of a significant number of molecules expressed in mammalian brains, which allows characterizing of the molecular and circuit basis for multi-sensory behavior during decision-making (Bargmann, 1998). In addition, studies have demonstrated various genes and neurons in behavioral differences previously observed in sensory behavior and decision-making when comparing different organisms, such as, nematodes. These variations in behavior involve differences in neuronal signals and neurons. For example, catecholamine signaling, neuropeptide Y-like receptors and pheromone chemoreceptors (Debono and Bargmann, 1998, Srinivasan et al., 2008; Bendesky et al., 2010, Mcgraph et al., 2011). In this study, we investigate the behavioral differences across various species of nematodes, by examining multiple types of Caenorhabditis species and how they may differ in a multi-sensory behavioral assay (Harris et al., 2019). The multisensory behavioral assay involves examining how different species of nematodes that are exposed to conflicting cues, behave when compared to the standard wild type, C. elegans Bristol N2 worms. We use a multi-sensory behavior paradigm to address these questions to determine any difference in 2-nonanone-dependent food leaving, that assesses food leaving during exposure to the repellent 2-nonanone. Wild type N2 C. elegans were examined as the control in comparison to other Caenorhabditis species, including, Caenorhabditis remanei (C. remanei), Caenorhabditis nouraguensis (C. nouraguensis), and Caenorhabditis portoensis (C. portoensis).
-
[
MicroPubl Biol,
2020]
Sensation of environmental cues and decisions made as a result of processing of specific sensory cues underlies a myriad of behavioral responses that control every-day life decisions and ultimately survival in many organisms. Despite the appreciation that organisms can sense, process, and translate sensory cues into a behavioral response, the neural mechanisms and molecules that mediate these behaviors are still unclear. Neurotransmitters, such as glutamate, have been implicated in a variety of sensory-dependent behavioral responses, including olfaction, nociception, mechanosensation, and gustation (Mugnaini et al., 1984, Wendy et al., 2013, Daghfous et al., 2018). Despite understanding the importance of glutamate signaling in sensation and translation of contextual cues on behavior, the molecular mechanisms underlying how glutamatergic transmission influences sensory behavior is not fully understood. The nematode, C. elegans, is able to sense a variety of sensory cues. These types of sensory-dependent behavioral responses are mediated through olfactory, gustatory, mechanosensory and aerotactic circuits of the worm (Lans and Jansen, 2004, Milward et al., 2011, Bretscher et al., 2011, Kodama-Namba et al., 2013, Ghosh et al., 2017). Odor guided behavior toward attractants, such as, food cues requires neurotransmitters, that include, glutamate (Chalasani et al., 2007, Chalasani et al., 2010). More specifically, once on a food source, wild type N2 hermaphrodites will generally be retained on a food source (Shtonda and Avery, 2006, Milward et al., 2011, Harris et al., 2019). The types, quality, pathogenicity, and perception of food can modulate food recognition, food leaving rates, and overall navigational strategies towards food (Zhang et al., 2005, Shtonda and Avery, 2006; Ollofsson et al., 2014). These types of behaviors are based on detection of environmental cues, including oxygen, metabolites, pheromones, and odors. Food leaving behaviors have been shown to be influenced by a number of neuronal signals (Shtonda and Avery, 2006, Bendesky et al., 2011, Ollofsson et al., 2014, Meisel et al., 2014, Hao et al., 2018).
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[
microPublication Biology,
2020]
An organisms behavior that promotes various behavioral and physiological responses can be influenced by olfactory behavior. Animals across the phyla constantly utilize chemosensory functions in order for survival (Lessing and Carlson, 1999, Ache and Young, 2005, Chaisson and Hallem, 2012). Organisms are also able to couple odor sensation with physiological responses and behavioral states to coordinate specific behavioral responses involved in bonding, social interaction, mating and feeding. For example, mammals, such as cats respond to odors using olfaction and respond based on processing of these types of cues at multiple levels of the brain to coordinate behavior (Hart et al., 1985, Miyazaki et al., 2017, Jacinto et al., 2018). Despite understanding these important strategies, the neural molecules and circuits underlying these behaviors are not fully understood. Cats respond to olfactory cues, including repulsive chemicals that drive avoidance behavior, such as, methyl nonyl ketone and others (Wolski et al., 1984). One repulsive spray that drives repulsion in many cats is Boundary. This cat repellent has been shown to produce an aversive response in cats.
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Chatzigeorgiou, Marios, Komuniecki, Richard, Hapiak, Vera, Harris, Gareth, Schafer, William, Wragg, Rachel
[
International Worm Meeting,
2009]
The ASH sensory neuron in C. elegans is polymodal, responding to both noxious (high osmolarity/volatile repellents) and mechanical (nose touch) stimuli to initiate backward locomotion. Examination of one ASH-mediated locomotory behavior, avoidance to octanol, has revealed that modulation of the ASH neural circuit is complex and involves multiple monoamines and distinct amine receptors (Wragg et al., 2007; Harris et al., 2009). In the present study, we have identified the monoamine receptors involved in another 5-HT stimulated ASH-mediated aversive response, nose touch. Like responses to octanol, multiple 5-HT receptors also have been identified in the food/5-HT sensitization of nose touch. For example, the expression of
ser-5 in the ASHs appears to be essential for 5-HT dependent increases in aversive responses to nose touch. In contrast, both TA and OA inhibit nose touch and two monoamine receptors (F14D12.6 and SER-3) appear to be involved in octopaminergic inhibition. These receptors are currently being localized in the ASH locomotory circuit. Using the calcium indicator cameleon, we analyzed ASH Ca2+ responses to nose touch in
ser-5 null animals. ASH Ca2+ transients were independent of exogenous 5-HT and more robust in
ser-5 null animals than in wild-type or
ser-4;
mod-1;
ser-7 ser-1 quadruple null animals that presumably only express
ser-5. Since we predict that SER-5 stimulates neurotransmitter release at the ASH synapse, the increased Ca2+ signaling in the ASH soma was surprising. We are currently exploring whether SER-5 signaling has other effects on the ASH or whether SER-5 also modulates the release of other ligands, perhaps peptides, that inhibit ASH Ca2+ dynamics.
-
[
International Worm Meeting,
2013]
*Authors contributed equally. Olfaction is an important means for animals to communicate with the environment, and experience can profoundly shape the representation of olfactory cues to an animal. Consistent findings from olfactory literature suggest that males and females detect, identify, and discriminate odors differently. However, little is known whether sex difference also influences olfactory learning. The nematode worm, Caenorhabditis elegans, feeds on bacteria in its natural environment but is susceptible to infection after the ingestion of harmful pathogenic bacteria. Because learning to avoid harmful food is essential for C. elegans survival, conditioned avoidance of odors associated with toxicity or infection is a robust form of olfactory learning. Previously, we have shown that naive hermaphrodites prefer the smell of the pathogenic bacteria P. aeruginosa (PA14) in comparison with the smell of the common lab food E. coli (OP50), and brief training with PA14 induces a learned olfactory aversion to the PA14 smell (Zhang et al., 2005, Ha et al., 2010). Here, we ask whether sex difference regulates olfactory learning. To this end, we used a high throughput micro-droplet assay system to measure the ability to learn to avoid the smell of PA14 in individual hermaphrodites or males. Preliminary data from our behavioral analysis has revealed that males exhibit defects in naive food odor preference as well as in learning, suggesting sex difference in olfactory plasticity. Previously, we have mapped a neural network that underlies the aversive olfactory learning (Ha et al., 2010). We plan to interrogate the effect of sex difference in this circuit that leads to the behavioral difference in olfactory learning. We hope that these studies will help further the understanding of how gender differences may influence olfactory behavior and plasticity in organisms such as humans.