The effects of sensitization on habituation using the olfactory jump reflex in Drosophila

Abstract only availableMemories can arise from simpler habituation and sensitization training as well as associative classical conditioning. However, in a complex environment, animals receive sensory cues in a fashion that can be more accurately described as having some habituation, sensitization and associative components. The relation between these types of memories at the molecular, systems and behavioral level remain largely unexplored. We can alter the timing of odor and electric shock presentation to induce all three types of memory in a defensive olfactory jump reflex. Habituation is a short-term change in behavior as a response to a repetitive stimulus. Using seven odors, we showed flies habituate their jump reflex to background levels of jump probabilities with ten odor presentations. Interestingly, the seven odors tested can be categorized into three groups based on their habituation rates: a high jump probability, a low jump probability, or a no-jump probability. Also, odors show some specificity as habituation of one odor does not lead to a total loss of jump response (complete cross-habituation) although it is reduced (partial cross-habituation). We chose to use six odors for further analysis. Sensitization is defined as an interference with habituation because of a dishabituating stimulus. Using electric shock as a potential sensitization cue, we presented shock and immediately tested jump probability. Interestingly, we found unpaired electric shock increased the jump probability with all odors tested, even those that do not induce a naïve jump. Classical (Pavlovian) conditioning arises when an animal associates a neutral stimulus with one that induces a reflex. Preliminary tests suggest that the paired presentation of electric shock and odor does not increase the jump probability of subsequent odor presentation. With the establishment of these three behavioral paradigms, the stage is set to investigate the interaction of habituation and sensitization on associate classical conditioning. Future experimentation should determine the relationship of the molecular and neural systems underlying these different forms of memory.Life Sciences Undergraduate Research Opportunity Progra

A century later another surprise: A non-visual behavioral function of the white gene

Abstract only availableDiscovery of the white mutation in Drosophila melanogaster has broadly influenced our understanding of the mechanisms of inheritance. We recently discovered a role of the white gene in memory formation. Thus, the white gene continues to provide insight into basic biological functions. We use two conditioning methods to routinely measure learning and memory in D. melanogaster, the heat-box, and classical olfactory conditioning. In the heat box experiments, white mutant flies' learning performance was notably impaired. However, in olfactory conditioning studies the mutant flies performed the same or better than wild-type flies. This differentiates the molecular mechanisms that support these conditioned behaviors. To better understand the regulatory elements that control white expression, we have initiated a molecular characterization of the white genomic locus. We identified the necessary regulatory elements by defining the deletion in the w1118 null allele. Using PCR methods we found that the deletion is about 7 kb long, and includes 5' regions, exon 1, and part of the first intron. Experiments to determine the sufficient set of regulatory elements for conditioned behavior were initiated. Two results argue that existing genomic transgenes do not contain all regulatory elements. First, mutations that affect eye color have molecular lesions outside a 14 kb genomic transgene. Second, attempted behavioral rescue experiments with this transgene fail. We interpret the failure of the 14 kb transgene to rescue as a consequence of incorrect white expression. Thus, we are creating a genomic construct that is 18 kb long that includes genomic DNA up to the next known gene. These approaches should define the regulatory regions necessary and sufficient for behaviorally important white expression.NSF-REU Program in Biological Sciences & Biochemistr

Heritability of Morphology in Brook Trout with Variable Life Histories

Distinct morphological variation is often associated with variation in life histories within and among populations of both plants and animals. In this study, we examined the heritability of morphology in three hatchery strains of brook trout (Salvelinus fontinalis), which were historically or are currently used for stocking and supplementation of both migratory and resident ecotypes in the upper Great Lakes region. In a common garden experiment, significant variation in body morphology was observed within and across populations sampled at three time periods. The most notable differences among strains were differences in dorso-ventral body depth and the shape of the caudal peduncle, with some differences in the anterior-posterior placement of the dorsal and ventral fins. Variation with and among 70 half-sib families indicates that heritabilities of morphology and body size were significant at most developmental time points both within and across strains. Heritabilities for morphological characters within strains ranged from 0 to 0.95 across time points. Significant within-strain heritabilities for length ranged from 0 to 0.93 across time points and for weight ranged from 0 to 0.88. Significant additive genetic variation exists within and across hatchery brook trout strains for morphology and size, indicating that these traits are capable of responding to natural or artificial selection

Place learning overrides innate behaviors in Drosophila

Animals in a natural environment confront many sensory cues. Some of these cues bias behavioral decisions independent of experience, and action selection can reveal a stimulus–response (S–R) connection. However, in a changing environment it would be a benefit for an animal to update behavioral action selection based on experience, and learning might modify even strong S–R relationships. How animals use learning to modify S–R relationships is a largely open question. Three sensory stimuli, air, light, and gravity sources were presented to individual Drosophila melanogaster in both naïve and place conditioning situations. Flies were tested for a potential modification of the S–R relationships of anemotaxis, phototaxis, and negative gravitaxis by a contingency that associated place with high temperature. With two stimuli, significant S–R relationships were abandoned when the cue was in conflict with the place learning contingency. The role of the dunce (dnc) cAMP-phosphodiesterase and the rutabaga (rut) adenylyl cyclase were examined in all conditions. Both dnc1 and rut2080 mutant flies failed to display significant S–R relationships with two attractive cues, and have characteristically lower conditioning scores under most conditions. Thus, learning can have profound effects on separate native S–R relationships in multiple contexts, and mutation of the dnc and rut genes reveal complex effects on behavior.</jats:p

The arouser EPS8L3 Gene Is Critical for Normal Memory in Drosophila

The genetic mechanisms that influence memory formation and sensitivity to the effects of ethanol on behavior in Drosophila have some common elements. So far, these have centered on the cAMP/PKA signaling pathway, synapsin and fas2-dependent processes, pumilio-dependent regulators of translation, and a few other genes. However, there are several genes that are important for one or the other behaviors, suggesting that there is an incomplete overlap in the mechanisms that support memory and ethanol sensitive behaviors. The basis for this overlap is far from understood. We therefore examined memory in arouser (aru) mutant flies, which have recently been identified as having ethanol sensitivity deficits. The aru mutant flies showed memory deficits in both short-term place memory and olfactory memory tests. Flies with a revertant aru allele had wild-type levels of memory performance, arguing that the aru gene, encoding an EPS8L3 product, has a role in Drosophila memory formation. Furthermore, and interestingly, flies with the aru8–128 insertion allele had deficits in only one of two genetic backgrounds in place and olfactory memory tests. Flies with an aru imprecise excision allele had deficits in tests of olfactory memory. Quantitative measurements of aru EPS8L3 mRNA expression levels correlate decreased expression with deficits in olfactory memory while over expression is correlated with place memory deficits. Thus, mutations of the aru EPS8L3 gene interact with the alleles of a particular genetic background to regulate arouser expression and reveals a role of this gene in memory

The conserved protein kinase-A target motif in synapsin of Drosophila is effectively modified by pre-mRNA editing.

RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are.BACKGROUND: Synapsins are abundant synaptic vesicle associated phosphoproteins that are involved in the fine regulation of neurotransmitter release. The Drosophila member of this protein family contains three conserved domains (A, C, and E) and is expressed in most or all synaptic terminals. Similar to mouse mutants, synapsin knock-out flies show no obvious structural defects but are disturbed in complex behaviour, notably learning and memory. RESULTS: We demonstrate that the N-terminal phosphorylation consensus motif RRxS that is conserved in all synapsins investigated so far, is modified in Drosophila by pre-mRNA editing. In mammals this motif represents the target site P1 of protein kinase A (PKA) and calcium/calmodulin dependent protein kinase I/IV. The result of this editing, by which RRFS is modified to RGFS, can be observed in cDNAs of larvae and adults and in both isolated heads and bodies. It is also seen in several newly collected wild-type strains and thus does not represent an adaptation to laboratory culture conditions. A likely editing site complementary sequence is found in a downstream intron indicating that the synapsin pre-mRNA can form a double-stranded RNA structure that is required for editing by the adenosine deaminase acting on RNA (ADAR) enzyme. A deletion in the Drosophila Adar gene generated by transposon remobilization prevents this modification, proving that the ADAR enzyme is responsible for the pre-mRNA editing described here. We also provide evidence for a likely function of synapsin editing in Drosophila. The N-terminal synapsin undeca-peptide containing the genomic motif (RRFS) represents an excellent substrate for in-vitro phosphorylation by bovine PKA while the edited peptide (RGFS) is not significantly phosphorylated. Thus pre-mRNA editing by ADAR could modulate the function of ubiquitously expressed synapsin in a cell-specific manner during development and adulthood. CONCLUSION: Similar to several other neuronal proteins of Drosophila, synapsin is modified by ADAR-mediated recoding at the pre-mRNA level. This editing likely reduces or abolishes synapsin phosphorylation by PKA. Since synapsin in Drosophila is required for various forms of behavioural plasticity, it will be fascinating to investigate the effect of this recoding on learning and memory.Published versio

Using simple nervous systems to investigate the neural basis of behavior

Neuroscience - Vision and Functional Brain Imaging Poster SessionThe human brain is remarkable, both in the sense that it helps us with a lifetime of decisions and memories, but also that it allows us to contemplate how the brain itself works. One concludes, however, pretty quickly that the human brain is quite complicated. The brain has an estimated 1011 neurons, and more than a thousand times more connections. How these neurons and connections work together in systems is a grand challenge in the neurosciences. Fortunately, we can use organisms with simpler nervous systems to understand basic principles of nervous system function. For example, the first insights into the generation of nerve cell action potentials were determined in a squid giant neuron. Principles derived from these neurons are incorporated into most or all computational models used today. Thus, one expects lessons learned in simpler nervous systems to have application in more complex organisms, including humans. A successful approach in understanding nervous system function is to examine the role that different neural systems play in regulating behavior. Broadly speaking these include processes that support sensory encoding, motor activity, and multisensory and sensory-motor integration. Animals have developed sensory systems to sense the world around them. Audition and temperature perception are two of a few of the sensory modalities that are critical for communication and detecting ideal environments. Katydid hearing systems solve perceptual problems that are common to all hearing systems, such as the recognition of complex temporal patterns, or the detection of important signals in noisy backgrounds. Remarkably, katydids solve these problems with a sensory system encompassing only few neurons. In other studies, the ability to sense temperatures has been addressed in the fruit fly Drosophila. One can differentiate between neural systems important for sensing relatively cool and warm temperatures. Motor systems are critical for several animal behaviors, from regulating gut activity to locomotion. Studies of nervous system ganglia in the crab and lobster have identified principles of nerve cell interactions and modulation. Furthermore, mechanisms regulating brain circuits that initiate swimming behavior in the lamprey tell us that they are similar in a wide variety of vertebrates. Finally, one can begin to understand cellular mechanisms of nervous system regeneration after spinal cord injury in simpler vertebrates that are able to behaviorally recover following such injuries. Multisensory and sensory-motor integration provide essential elements for plasticity in the nervous system. The trigeminal system in the lamprey provide a starting point to determine how sensory inputs feed into brain locomotor command systems to initiate behavior. Also, plasticity underlying longer-lived changes in behavior with learning can be addressed in studies of memory formation. In Drosophila, several molecular and neural systems underlying multiple forms of memory have been identified, including implications of cAMP / PKA activity and serotonin reinforcement. Thus, one can use relatively simple organisms, from insects and crustaceans to lamprey, in determining principles of nervous system function. Results at the sensory, motor, and integrative levels are expected to influence our understanding of more complex systems

The Radish Gene Reveals a Memory Component with Variable Temporal Properties

Memory phases, dependent on different neural and molecular mechanisms, strongly influence memory performance. Our understanding, however, of how memory phases interact is far from complete. In Drosophila, aversive olfactory learning is thought to progress from short-term through long-term memory phases. Another memory phase termed anesthesia resistant memory, dependent on the radish gene, influences memory hours after aversive olfactory learning. How does the radish-dependent phase influence memory performance in different tasks? It is found that the radish memory component does not scale with the stability of several memory traces, indicating a specific recruitment of this component to influence different memories, even within minutes of learning

The serotonergic central nervous system of the Drosophila larva: anatomy and behavioral function.

The Drosophila larva has turned into a particularly simple model system for studying the neuronal basis of innate behaviors and higher brain functions. Neuronal networks involved in olfaction, gustation, vision and learning and memory have been described during the last decade, often up to the single-cell level. Thus, most of these sensory networks are substantially defined, from the sensory level up to third-order neurons. This is especially true for the olfactory system of the larva. Given the wealth of genetic tools in Drosophila it is now possible to address the question how modulatory systems interfere with sensory systems and affect learning and memory. Here we focus on the serotonergic system that was shown to be involved in mammalian and insect sensory perception as well as learning and memory. Larval studies suggested that the serotonergic system is involved in the modulation of olfaction, feeding, vision and heart rate regulation. In a dual anatomical and behavioral approach we describe the basic anatomy of the larval serotonergic system, down to the single-cell level. In parallel, by expressing apoptosis-inducing genes during embryonic and larval development, we ablate most of the serotonergic neurons within the larval central nervous system. When testing these animals for naïve odor, sugar, salt and light perception, no profound phenotype was detectable; even appetitive and aversive learning was normal. Our results provide the first comprehensive description of the neuronal network of the larval serotonergic system. Moreover, they suggest that serotonin per se is not necessary for any of the behaviors tested. However, our data do not exclude that this system may modulate or fine-tune a wide set of behaviors, similar to its reported function in other insect species or in mammals. Based on our observations and the availability of a wide variety of genetic tools, this issue can now be addressed

TrpA1 Regulates Thermal Nociception in Drosophila

Pain is a significant medical concern and represents a major unmet clinical need. The ability to perceive and react to tissue-damaging stimuli is essential in order to maintain bodily integrity in the face of environmental danger. To prevent damage the systems that detect noxious stimuli are therefore under strict evolutionary pressure. We developed a high-throughput behavioral method to identify genes contributing to thermal nociception in the fruit fly and have reported a large-scale screen that identified the Ca2+ channel straightjacket (stj) as a conserved regulator of thermal nociception. Here we present the minimal anatomical and neuronal requirements for Drosophila to avoid noxious heat in our novel behavioral paradigm. Bioinformatics analysis of our whole genome data set revealed 23 genes implicated in Ca2+ signaling that are required for noxious heat avoidance. One of these genes, the conserved thermoreceptor TrpA1, was confirmed as a bona fide “pain” gene in both adult and larval fly nociception paradigms. The nociceptive function of TrpA1 required expression within the Drosophila nervous system, specifically within nociceptive multi-dendritic (MD) sensory neurons. Therefore, our analysis identifies the channel TRPA1 as a conserved regulator of nociception