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Wada-Katsumata A, Schal C. Olfactory Learning Supports an Adaptive Sugar-Aversion Gustatory Phenotype in the German Cockroach. INSECTS 2021; 12:insects12080724. [PMID: 34442290 PMCID: PMC8397102 DOI: 10.3390/insects12080724] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/15/2021] [Revised: 08/09/2021] [Accepted: 08/09/2021] [Indexed: 11/16/2022]
Abstract
Simple Summary Toxic baits that contain an insecticide and phagosimulatory sugars, including glucose, are most effective in German cockroach control. However, cockroaches have evolved behavioral resistance, where they perceive glucose as a deterrent and avoid eating the bait (glucose-aversion, GA), resulting in failure to control infestations. We hypothesized that the GA phenotype may be extended by associative learning of specific odors with glucose. We demonstrated that GA cockroaches associated attractive food odors, such as vanilla and chocolate, with glucose (deterrent) and learned to avoid these odors. In contrast, wild type (WT) cockroaches that associated these odors with glucose (phagostimulant) increased their preference for the odors. The aversive and appetitive memories were retained for at least three days. Generally, when toxic baits are deployed, GA cockroaches are first attracted to the bait, and they repeatedly experience its aversive taste as they reject eating the deterrent bait. The recurring non-rewarding foraging experience may contribute to the formation of an aversive olfactory memory. Even if the baits are later reformulated without aversive tastants, GA cockroaches may avoid the new bait because they associate it with aversive olfactory stimuli. Our findings will guide the rational development of baits that consider the olfactory learning abilities of cockroaches. Abstract An association of food sources with odors prominently guides foraging behavior in animals. To understand the interaction of olfactory memory and food preferences, we used glucose-averse (GA) German cockroaches. Multiple populations of cockroaches evolved a gustatory polymorphism where glucose is perceived as a deterrent and enables GA cockroaches to avoid eating glucose-containing toxic baits. Comparative behavioral analysis using an operant conditioning paradigm revealed that learning and memory guide foraging decisions. Cockroaches learned to associate specific food odors with fructose (phagostimulant, reward) within only a 1 h conditioning session, and with caffeine (deterrent, punishment) after only three 1 h conditioning sessions. Glucose acted as reward in wild type (WT) cockroaches, but GA cockroaches learned to avoid an innately attractive odor that was associated with glucose. Olfactory memory was retained for at least 3 days after three 1 h conditioning sessions. Our results reveal that specific tastants can serve as potent reward or punishment in olfactory associative learning, which reinforces gustatory food preferences. Olfactory learning, therefore, reinforces behavioral resistance of GA cockroaches to sugar-containing toxic baits. Cockroaches may also generalize their olfactory learning to baits that contain the same or similar attractive odors even if they do not contain glucose.
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Durrieu M, Wystrach A, Arrufat P, Giurfa M, Isabel G. Fruit flies can learn non-elemental olfactory discriminations. Proc Biol Sci 2020; 287:20201234. [PMID: 33171086 PMCID: PMC7735272 DOI: 10.1098/rspb.2020.1234] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2020] [Accepted: 10/19/2020] [Indexed: 12/25/2022] Open
Abstract
Associative learning allows animals to establish links between stimuli based on their concomitance. In the case of Pavlovian conditioning, a single stimulus A (the conditional stimulus, CS) is reinforced unambiguously with an unconditional stimulus (US) eliciting an innate response. This conditioning constitutes an 'elemental' association to elicit a learnt response from A+ without US presentation after learning. However, associative learning may involve a 'complex' CS composed of several components. In that case, the compound may predict a different outcome than the components taken separately, leading to ambiguity and requiring the animal to perform so-called non-elemental discrimination. Here, we focus on such a non-elemental task, the negative patterning (NP) problem, and provide the first evidence of NP solving in Drosophila. We show that Drosophila learn to discriminate a simple component (A or B) associated with electric shocks (+) from an odour mixture composed either partly (called 'feature-negative discrimination' A+ versus AB-) or entirely (called 'NP' A+B+ versus AB-) of the shock-associated components. Furthermore, we show that conditioning repetition results in a transition from an elemental to a configural representation of the mixture required to solve the NP task, highlighting the cognitive flexibility of Drosophila.
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Affiliation(s)
- Matthias Durrieu
- Research Centre on Animal Cognition, Centre for Integrative Biology, CNRS, University of Toulouse, 118 route de Narbonne, F-31062 Toulouse, France
| | - Antoine Wystrach
- Research Centre on Animal Cognition, Centre for Integrative Biology, CNRS, University of Toulouse, 118 route de Narbonne, F-31062 Toulouse, France
| | - Patrick Arrufat
- Research Centre on Animal Cognition, Centre for Integrative Biology, CNRS, University of Toulouse, 118 route de Narbonne, F-31062 Toulouse, France
| | - Martin Giurfa
- Research Centre on Animal Cognition, Centre for Integrative Biology, CNRS, University of Toulouse, 118 route de Narbonne, F-31062 Toulouse, France
- College of Animal Science (College of Bee Science), Fujian Agriculture and Forestry University, Fuzhou 350002, China
- Institut Universitaire de France (IUF), Paris, France
| | - Guillaume Isabel
- Research Centre on Animal Cognition, Centre for Integrative Biology, CNRS, University of Toulouse, 118 route de Narbonne, F-31062 Toulouse, France
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Arican C, Bulk J, Deisig N, Nawrot MP. Cockroaches Show Individuality in Learning and Memory During Classical and Operant Conditioning. Front Physiol 2020; 10:1539. [PMID: 31969831 PMCID: PMC6960104 DOI: 10.3389/fphys.2019.01539] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2019] [Accepted: 12/05/2019] [Indexed: 12/05/2022] Open
Abstract
Animal personality and individuality are intensively researched in vertebrates and both concepts are increasingly applied to behavioral science in insects. However, only few studies have looked into individuality with respect to performance in learning and memory tasks. In vertebrates, individual learning capabilities vary considerably with respect to learning speed and learning rate. Likewise, honeybees express individual learning abilities in a wide range of classical conditioning protocols. Here, we study individuality in the learning and memory performance of cockroaches, both in classical and operant conditioning tasks. We implemented a novel classical (olfactory) conditioning paradigm where the conditioned response is established in the maxilla-labia response (MLR). Operant spatial learning was investigated in a forced two-choice task using a T-maze. Our results confirm individual learning abilities in classical conditioning of cockroaches that was reported for honeybees and vertebrates but contrast long-standing reports on stochastic learning behavior in fruit flies. In our experiments, most learners expressed a correct behavior after only a single learning trial showing a consistent high performance during training and test. We can further show that individual learning differences in insects are not limited to classical conditioning but equally appear in operant conditioning of the cockroach.
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Affiliation(s)
| | | | - Nina Deisig
- Department of Computational Systems Neuroscience, Institute of Zoology, University of Cologne, Cologne, Germany
| | - Martin Paul Nawrot
- Department of Computational Systems Neuroscience, Institute of Zoology, University of Cologne, Cologne, Germany
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Schoofs L, De Loof A, Van Hiel MB. Neuropeptides as Regulators of Behavior in Insects. ANNUAL REVIEW OF ENTOMOLOGY 2017; 62:35-52. [PMID: 27813667 DOI: 10.1146/annurev-ento-031616-035500] [Citation(s) in RCA: 111] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Neuropeptides are by far the largest and most diverse group of signaling molecules in multicellular organisms. They are ancient molecules important in regulating a multitude of processes. Their small proteinaceous character allowed them to evolve and radiate quickly into numerous different molecules. On average, hundreds of distinct neuropeptides are present in animals, sometimes with unique classes that do not occur in distantly related species. Acting as neurotransmitters, neuromodulators, hormones, or growth factors, they are extremely diverse and are involved in controlling growth, development, ecdysis, digestion, diuresis, and many more physiological processes. Neuropeptides are also crucial in regulating myriad behavioral actions associated with feeding, courtship, sleep, learning and memory, stress, addiction, and social interactions. In general, behavior ensures that an organism can survive in its environment and is defined as any action that can change an organism's relationship to its surroundings. Even though the mode of action of neuropeptides in insects has been vigorously studied, relatively little is known about most neuropeptides and only a few model insects have been investigated. Here, we provide an overview of the roles neuropeptides play in insect behavior. We conclude that multiple neuropeptides need to work in concert to coordinate certain behaviors. Additionally, most neuropeptides studied to date have more than a single function.
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Affiliation(s)
- Liliane Schoofs
- Functional Genomics and Proteomics Group, Department of Biology, KU Leuven, 3000 Leuven, Belgium; , ,
| | - Arnold De Loof
- Functional Genomics and Proteomics Group, Department of Biology, KU Leuven, 3000 Leuven, Belgium; , ,
| | - Matthias Boris Van Hiel
- Functional Genomics and Proteomics Group, Department of Biology, KU Leuven, 3000 Leuven, Belgium; , ,
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Hosono S, Matsumoto Y, Mizunami M. Interaction of inhibitory and facilitatory effects of conditioning trials on long-term memory formation. ACTA ACUST UNITED AC 2016; 23:669-678. [PMID: 27918270 PMCID: PMC5110985 DOI: 10.1101/lm.043513.116] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2016] [Accepted: 08/17/2016] [Indexed: 01/27/2023]
Abstract
Animals learn through experience and consolidate the memories into long-time storage. Conditioning parameters to induce protein synthesis-dependent long-term memory (LTM) have been the subject of extensive studies in many animals. Here we found a case in which a conditioning trial inhibits or facilitates LTM formation depending on the intervals from preceding trials. We studied the effects of conditioning parameters on LTM formation in olfactory conditioning of maxillary-palpi extension response with sucrose reward in the cockroach Periplaneta americana. We found, at first, that translation- and transcription-dependent LTM forms 1 h after training, the fastest so far reported in insects. Second, we observed that multiple-trial training with an intertrial interval (ITI) of 20 or 30 sec, often called massed training, is more effective than spaced training for LTM formation, an observation that differs from the results of most studies in other animals. Third, we found that a conditioning trial inhibits LTM formation when the intervals from preceding trials were in the range of 10–16 min. This inhibitory effect is pairing-specific and is not due to decreased motivation for learning (overtraining effect). To our knowledge, no similar inhibition of LTM formation by a conditioning trial has been reported in any animals. We propose a model to account for the effects of trial number and ITIs on LTM formation. Olfactory conditioning in cockroaches should provide pertinent materials in which to study neuronal and molecular mechanisms underlying the inhibitory and facilitatory processes for LTM formation.
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Affiliation(s)
- Shouhei Hosono
- Graduate School of Life Science, Hokkaido University, Sapporo 060-0810, Japan.,Graduate School of Agriculture, Tamagawa University, Machida 194-8610, Japan
| | - Yukihisa Matsumoto
- Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan.,Faculty of Liberal Arts, Tokyo Medical and Dental University, Ichikawa 272-0827, Japan
| | - Makoto Mizunami
- Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan
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Dopamine- and Tyrosine Hydroxylase-Immunoreactive Neurons in the Brain of the American Cockroach, Periplaneta americana. PLoS One 2016; 11:e0160531. [PMID: 27494326 PMCID: PMC4975486 DOI: 10.1371/journal.pone.0160531] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2016] [Accepted: 07/19/2016] [Indexed: 11/19/2022] Open
Abstract
The catecholamine dopamine plays several vital roles in the central nervous system of many species, but its neural mechanisms remain elusive. Detailed neuroanatomical characterization of dopamine neurons is a prerequisite for elucidating dopamine’s actions in the brain. In the present study, we investigated the distribution of dopaminergic neurons in the brain of the American cockroach, Periplaneta americana, using two antisera: 1) an antiserum against dopamine, and 2) an antiserum against tyrosine hydroxylase (TH, an enzyme required for dopamine synthesis), and identified about 250 putatively dopaminergic neurons. The patterns of dopamine- and TH-immunoreactive neurons were strikingly similar, suggesting that both antisera recognize the same sets of “dopaminergic” neurons. The dopamine and TH antibodies intensively or moderately immunolabeled prominent brain neuropils, e.g. the mushroom body (memory center), antennal lobe (first-order olfactory center) and central complex (motor coordination center). All subdivisions of the mushroom body exhibit both dopamine and TH immunoreactivity. Comparison of immunolabeled neurons with those filled by dye injection revealed that a group of immunolabeled neurons with cell bodies near the calyx projects into a distal region of the vertical lobe, which is a plausible site for olfactory memory formation in insects. In the antennal lobe, ordinary glomeruli as well as macroglomeruli exhibit both dopamine and TH immunoreactivity. It is noteworthy that the dopamine antiserum labeled tiny granular structures inside the glomeruli whereas the TH antiserum labeled processes in the marginal regions of the glomeruli, suggesting a different origin. In the central complex, all subdivisions excluding part of the noduli and protocerebral bridge exhibit both dopamine and TH immunoreactivity. These anatomical findings will accelerate our understanding of dopaminergic systems, specifically in neural circuits underlying aversive memory formation and arousal, in insects.
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Perry CJ, Barron AB, Cheng K. Invertebrate learning and cognition: relating phenomena to neural substrate. WILEY INTERDISCIPLINARY REVIEWS. COGNITIVE SCIENCE 2013; 4:561-582. [PMID: 26304245 DOI: 10.1002/wcs.1248] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/22/2013] [Revised: 05/28/2013] [Accepted: 07/06/2013] [Indexed: 02/04/2023]
Abstract
Diverse invertebrate species have been used for studies of learning and comparative cognition. Although we have gained invaluable information from this, in this study we argue that our approach to comparative learning research is rather deficient. Generally invertebrate learning research has focused mainly on arthropods, and most of that within the Hymenoptera and Diptera. Any true comparative analysis of the distribution of comparative cognitive abilities across phyla is hampered by this bias, and more fundamentally by a reporting bias toward positive results. To understand the limits of learning and cognition for a species, knowing what animals cannot do is at least as important as reporting what they can. Finally, much more effort needs to be focused on the neurobiological analysis of different types of learning to truly understand the differences and similarities of learning types. In this review, we first give a brief overview of the various forms of learning in invertebrates. We also suggest areas where further study is needed for a more comparative understanding of learning. Finally, using what is known of learning in honeybees and the well-studied honeybee brain, we present a model of how various complex forms of learning may be accounted for with the same neural circuitry required for so-called simple learning types. At the neurobiological level, different learning phenomena are unlikely to be independent, and without considering this it is very difficult to correctly interpret the phylogenetic distribution of learning and cognitive abilities. WIREs Cogn Sci 2013, 4:561-582. doi: 10.1002/wcs.1248 For further resources related to this article, please visit the WIREs website.
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Affiliation(s)
- Clint J Perry
- Department of Biological Sciences, Macquarie University, Sydney, NSW, Australia
| | - Andrew B Barron
- Department of Biological Sciences, Macquarie University, Sydney, NSW, Australia
| | - Ken Cheng
- Department of Biological Sciences, Macquarie University, Sydney, NSW, Australia
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Mushroom body extrinsic neurons in the honeybee brain encode cues and contexts differently. J Neurosci 2013; 33:7154-64. [PMID: 23616525 DOI: 10.1523/jneurosci.1331-12.2013] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Free-flying honeybees (Apis mellifera carnica) are known to learn the context to solve discrimination tasks. Here we apply classical conditioning of the proboscis extension response in restrained bees in combination with single-unit extracellular recordings from mushroom body (MB) extrinsic neurons elucidating the neural correlates of context-dependent olfactory discrimination. The contexts were light, colors, and temperatures, either alone or in combination. We found that bees learn context rules quickly and use them for better discrimination. They also solved a transwitching and a cue/context reversal task. Neurons extrinsic to the α lobe of the MB reduced the responses to the rewarded odor, whereas they increased their responses to the context. These results indicate that MB extrinsic neurons encode cues and contexts differently. Data are discussed with reference to MB function.
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Context-dependent olfactory learning monitored by activities of salivary neurons in cockroaches. Neurobiol Learn Mem 2012; 97:30-6. [DOI: 10.1016/j.nlm.2011.08.010] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2011] [Revised: 08/05/2011] [Accepted: 08/19/2011] [Indexed: 11/22/2022]
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Nishino H, Iwasaki M, Yasuyama K, Hongo H, Watanabe H, Mizunami M. Visual and olfactory input segregation in the mushroom body calyces in a basal neopteran, the American cockroach. ARTHROPOD STRUCTURE & DEVELOPMENT 2012; 41:3-16. [PMID: 22001372 DOI: 10.1016/j.asd.2011.08.005] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/04/2011] [Revised: 08/16/2011] [Accepted: 08/23/2011] [Indexed: 05/31/2023]
Abstract
The cockroach Periplaneta americana is an evolutionary basal neopteran insect, equipped with one of the largest and most elaborate mushroom bodies among insects. Using intracellular recording and staining in the protocerebrum, we discovered two new types of neurons that receive direct input from the optic lobe in addition to the neuron previously reported. These neurons have dendritic processes in the optic lobe, projection sites in the optic tracts, and send axonal terminals almost exclusively to the innermost layer of the MB calyces (input site of MB). Their responses were excitatory to visual but inhibitory to olfactory stimuli, and weak excitation occurred in response to mechanosensory stimuli to cerci. In contrast, interneurons with dendrites mainly in the antennal lobe projection sites send axon terminals to the middle to outer layers of the calyces. These were excited by various olfactory stimuli and mechanosensory stimuli to the antenna. These results suggest that there is general modality-specific terminal segregation in the MB calyces and that this is an early event in insect evolution. Possible postsynaptic and presynaptic elements of these neurons are discussed.
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Affiliation(s)
- Hiroshi Nishino
- Research Institute for Electronic Science, Hokkaido University, Sapporo 060-0812, Japan.
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Young JM, Wessnitzer J, Armstrong JD, Webb B. Elemental and non-elemental olfactory learning in Drosophila. Neurobiol Learn Mem 2011; 96:339-52. [PMID: 21742045 DOI: 10.1016/j.nlm.2011.06.009] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2010] [Revised: 06/05/2011] [Accepted: 06/17/2011] [Indexed: 11/17/2022]
Abstract
Brain complexity varies across many orders of magnitude between animals, and it is often assumed that complexity underpins cognition. It is thus important to explore the cognitive capacity of widely used model organisms such as Drosophila. We systematically investigated the fly's ability to learn discriminations involving compound olfactory stimuli associated with shock. Flies could distinguish binary mixtures (AB+ CD-), including overlapping mixtures (AB+ BC-). They could learn positive patterning (AB+A- B-) but could not learn negative patterning (A+ B+ AB-) or solve a biconditional discrimination task (AB+ CD+ AC- BD-). Learning about the elements of a compound (AB+) was not affected by prior conditioning of one of the elements (A+ AB+): flies do not exhibit blocking in this task. We compare these results with the predictions from simulation of several well-known theoretical models of learning, and find none are fully consistent with the overall pattern of observed behaviour.
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Affiliation(s)
- J M Young
- Institute for Perception, Action & Behaviour, University of Edinburgh, EH8 9AB, United Kingdom.
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A model of non-elemental olfactory learning in Drosophila. J Comput Neurosci 2011; 32:197-212. [DOI: 10.1007/s10827-011-0348-6] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2011] [Revised: 04/29/2011] [Accepted: 05/31/2011] [Indexed: 10/18/2022]
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Wada-Katsumata A, Silverman J, Schal C. Differential Inputs from Chemosensory Appendages Mediate Feeding Responses to Glucose in Wild-Type and Glucose-Averse German Cockroaches, Blattella germanica. Chem Senses 2011; 36:589-600. [DOI: 10.1093/chemse/bjr023] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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Bos N, Guerrieri FJ, d’Ettorre P. Significance of chemical recognition cues is context dependent in ants. Anim Behav 2010. [DOI: 10.1016/j.anbehav.2010.08.001] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
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Watanabe H, Sato C, Kuramochi T, Nishino H, Mizunami M. Salivary conditioning with antennal gustatory unconditioned stimulus in an insect. Neurobiol Learn Mem 2008; 90:245-54. [DOI: 10.1016/j.nlm.2008.03.009] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2008] [Revised: 03/22/2008] [Accepted: 03/24/2008] [Indexed: 11/15/2022]
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No evidence for visual context-dependency of olfactory learning in Drosophila. Naturwissenschaften 2008; 95:767-74. [PMID: 18443757 PMCID: PMC2443390 DOI: 10.1007/s00114-008-0380-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2007] [Revised: 03/17/2008] [Accepted: 03/19/2008] [Indexed: 02/04/2023]
Abstract
How is behaviour organised across sensory modalities? Specifically, we ask concerning the fruit fly Drosophila melanogaster how visual context affects olfactory learning and recall and whether information about visual context is getting integrated into olfactory memory. We find that changing visual context between training and test does not deteriorate olfactory memory scores, suggesting that these olfactory memories can drive behaviour despite a mismatch of visual context between training and test. Rather, both the establishment and the recall of olfactory memory are generally facilitated by light. In a follow-up experiment, we find no evidence for learning about combinations of odours and visual context as predictors for reinforcement even after explicit training in a so-called biconditional discrimination task. Thus, a ‘true’ interaction between visual and olfactory modalities is not evident; instead, light seems to influence olfactory learning and recall unspecifically, for example by altering motor activity, alertness or olfactory acuity.
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Watanabe H, Mizunami M. Pavlov's cockroach: classical conditioning of salivation in an insect. PLoS One 2007; 2:e529. [PMID: 17565382 PMCID: PMC1885829 DOI: 10.1371/journal.pone.0000529] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2007] [Accepted: 05/19/2007] [Indexed: 11/18/2022] Open
Abstract
Secretion of saliva to aid swallowing and digestion is an important physiological function found in many vertebrates and invertebrates. Pavlov reported classical conditioning of salivation in dogs a century ago. Conditioning of salivation, however, has been so far reported only in dogs and humans, and its underlying neural mechanisms remain elusive because of the complexity of the mammalian brain. We previously reported that, in cockroaches Periplaneta americana, salivary neurons that control salivation exhibited increased responses to an odor after conditioning trials in which the odor was paired with sucrose solution. However, no direct evidence of conditioning of salivation was obtained. In this study, we investigated the effects of conditioning trials on the level of salivation. Untrained cockroaches exhibited salivary responses to sucrose solution applied to the mouth but not to peppermint or vanilla odor applied to an antenna. After differential conditioning trials in which an odor was paired with sucrose solution and another odor was presented without pairing with sucrose solution, sucrose-associated odor induced an increase in the level of salivation, but the odor presented alone did not. The conditioning effect lasted for one day after conditioning trials. This study demonstrates, for the first time, classical conditioning of salivation in species other than dogs and humans, thereby providing the first evidence of sophisticated neural control of autonomic function in insects. The results provide a useful model system for studying cellular basis of conditioning of salivation in the simpler nervous system of insects.
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Affiliation(s)
| | - Makoto Mizunami
- Graduate School of Life Sciences, Tohoku University, Sendai, Japan
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