Short-term memories in Drosophila are governed by general and specific genetic systems

Mass Spectrometry Imaging Shows Modafinil, A Student Study Drug, Changes the Lipid Composition of the Fly Brain

Modafinil, a widely used psychoactive drug, has been shown to exert a positive impact on cognition and is used to treat sleep disorders and hyperactivity. Using time-of-flight secondary ion mass spectrometric imaging, we studied the changes of brain lipids of Drosophila melanogaster induced by modafinil to gain insight into the functional mechanism of modafinil in the brain. We found that upon modafinil treatment, the abundance of phosphatidylcholine and sphingomyelin species in the central brain of Drosophila is significantly decreased, whereas the levels of phosphatidylethanolamine and phosphatidylinositol in the brains show significant enhancement compared to the control flies. The alteration of brain lipids caused by modafinil is consistent with previous studies about cognition-related drugs and offers a plausible mechanism regarding the action of modafinil in the brain as well as a potential target for the treatment of certain disorders.

Cellular and circuit mechanisms of olfactory associative learning in Drosophila

Recent years have witnessed significant progress in understanding how memories are encoded, from the molecular to the cellular and the circuit/systems levels. With a good compromise between brain complexity and behavioral sophistication, the fruit fly Drosophila melanogaster is one of the preeminent animal models of learning and memory. Here we review how memories are encoded in Drosophila, with a focus on short-term memory and an eye toward future directions. Forward genetic screens have revealed a large number of genes and transcripts necessary for learning and memory, some acting cell-autonomously. Further, the relative numerical simplicity of the fly brain has enabled the reverse engineering of learning circuits with remarkable precision, in some cases ascribing behavioral phenotypes to single neurons. Functional imaging and physiological studies have localized and parsed the plasticity that occurs during learning at some of the major loci. Connectomics projects are significantly expanding anatomical knowledge of the nervous system, filling out the roadmap for ongoing functional/physiological and behavioral studies, which are being accelerated by simultaneous tool development. These developments have provided unprecedented insight into the fundamental neural principles of learning, and lay the groundwork for deep understanding in the near future.

Working Memory: It's a Gas, Gas, Gas

The ellipsoid body, a doughnut-shaped part of the fly brain, is essential for visual working memory. Gaseous second messengers establish a functional ellipsoid body and act as a short-term aid in orientation behavior.

Learning Situations in Nursing Education: A Concept Analysis

Background and purpose:

The nursing student requires opportunities to learn within authentic contexts so as to enable safe and competent practice. One strategy to facilitate such learning is the creation of learning situations. A lack of studies on the learning situation in nursing and other health care fields has resulted in insufficient knowledge of the characteristics of the learning situation, its antecedents, and consequences. Nurse educators need to have comprehensive and practical knowledge of the definition and characteristics of the learning situation so as to enable their students to achieve enhanced learning outcomes. The aim of this study was to clarify the concept of the learning situation as it relates to the education of nurses and improve understanding of its characteristics, antecedents, and consequences.

Methods:

The Bonis method of concept analysis, as derived from the Rodgers’ evolutionary method, provided the framework for analysis. Data collection and analysis were undertaken in two phases: “interdisciplinary” and “intra-disciplinary.” The data source was a search of the literature, encompassing nursing and allied health care professions, published from 1975 to 2016.

Results:

No agreement on the conceptual phenomenon was discovered in the international literature. The concept of a learning situation was used generally in two ways and thus classified into the themes of: “formal/informal learning situation” and “biologic/nonbiologic learning situation.” Antecedents to the creation of a learning situation included personal and environmental factors. The characteristics of a learning situation were described in terms of being complex, dynamic, and offering potential and effective learning opportunities. Consequences of the learning situation included enhancement of the students’ learning, professionalization, and socialization into the professional role.

Implication for Practice:

The nurse educator, when considering the application of the concept of a learning situation in their educational planning, must acknowledge that the application of this concept will include the student’s clinical learning experiences. More studies are required to determine factors influencing the creation of a successful learning situation from the perspectives of nurse educators and nursing students, clinical nurses and patients.

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.

A Presynaptic Function of Shank Protein in Drosophila

Human genetic studies support that loss-of-function mutations in the SH3 domain and ankyrin repeat containing family proteins (SHANK1-3), the large synaptic scaffolding proteins enriched at the postsynaptic density of excitatory synapses, are causative for autism spectrum disorder and other neuropsychiatric disorders in humans. To better understand the in vivo functions of Shank and facilitate dissection of neuropathology associated with SHANK mutations in human, we generated multiple mutations in the Shank gene, the only member of the SHANK family in Drosophila melanogaster Both male and female Shank null mutants were fully viable and fertile with no apparent morphological or developmental defects. Expression analysis revealed apparent enrichment of Shank in the neuropils of the CNS. Specifically, Shank coexpressed with another PSD scaffold protein, Homer, in the calyx of mushroom bodies in the brain. Consistent with high expression in mushroom body calyces, Shank mutants show an abnormal calyx structure and reduced olfactory acuity. These morphological and functional phenotypes were fully rescued by pan-neuronal reexpression of Shank, and only partially rescued by presynaptic but no rescue by postsynaptic reexpression of Shank. Our findings thus establish a previously unappreciated presynaptic function of Shank.SIGNIFICANCE STATEMENT Mutations in SHANK family genes are causative for idiopathic autism spectrum disorder. To understand the neural function of Shank, a large scaffolding protein enriched at the postsynaptic densities, we examined the role of Drosophila Shank in synapse development at the peripheral neuromuscular junctions and the central mushroom body calyx. Our results demonstrate that, in addition to its conventional postsynaptic function, Shank also acts presynaptically in synapse development in the brain. This study offers novel insights into the synaptic role of Shank.

The Drosophila melanogaster tribbles pseudokinase is necessary for proper memory formation

The tribbles (trbl) pseudokinases play important roles in signaling and physiology in multiple contexts, ranging from innate immunity to cancer, suggesting fundamental cellular functions for the trbls' gene products. Despite expression of the trbl pseudokinases in the nervous systems of invertebrate and vertebrate animals, and evidence that they have a function within mouse and human dopamine neurons, there is no clear case for a function of a Trbl protein that influences behavior. Indeed, the first and only evidence for this type of function comes from Drosophila melanogaster, where a mutation of the single trbl gene was identified in a genetic screen for short-term memory mutant flies. The current study tested flies containing multiple trbl mutant alleles and potential transgenic rescue in both operant place memory and classical olfactory memory paradigms. Genetic complementation tests and transgenic rescue of memory phenotypes in both paradigms show that the D. melanogaster trbl pseudokinase is essential for proper memory formation. Expression analysis with a polyclonal antiserum against Trbl shows that the protein is expressed widely in the fly brain, with higher expression in the cellular rind than the neuropil. Rescue of the behavioral phenotype with transgenic expression indicates the trbl function can be localized to a subset of the nervous system. Thus, we provide the first compelling case for the function of a trbl pseudokinase in the regulation of behavior.

The Gyc76C Receptor Guanylyl Cyclase and the Foraging cGMP-Dependent Kinase Regulate Extracellular Matrix Organization and BMP Signaling in the Developing Wing of Drosophila melanogaster

The developing crossveins of the wing of Drosophila melanogaster are specified by long-range BMP signaling and are especially sensitive to loss of extracellular modulators of BMP signaling such as the Chordin homolog Short gastrulation (Sog). However, the role of the extracellular matrix in BMP signaling and Sog activity in the crossveins has been poorly explored. Using a genetic mosaic screen for mutations that disrupt BMP signaling and posterior crossvein development, we identify Gyc76C, a member of the receptor guanylyl cyclase family that includes mammalian natriuretic peptide receptors. We show that Gyc76C and the soluble cGMP-dependent kinase Foraging, likely linked by cGMP, are necessary for normal refinement and maintenance of long-range BMP signaling in the posterior crossvein. This does not occur through cell-autonomous crosstalk between cGMP and BMP signal transduction, but likely through altered extracellular activity of Sog. We identify a novel pathway leading from Gyc76C to the organization of the wing extracellular matrix by matrix metalloproteinases, and show that both the extracellular matrix and BMP signaling effects are largely mediated by changes in the activity of matrix metalloproteinases. We discuss parallels and differences between this pathway and other examples of cGMP activity in both Drosophila melanogaster and mammalian cells and tissues.

Signaling between cells regulates many processes, including the choices cells make between different fates during development and regeneration, and misregulation of such signaling underlies many human pathologies. To understand how such signals control developmental decisions, it is necessary to elucidate both how cells regulate and respond to different levels of signaling, and how different types of signals combine and regulate each other. We have used genetic screening in the fruitfly Drosophila melanogaster to identify mutations that reduce or eliminate signals carried by Bone Morphogenetic Proteins (BMPs), and show that BMP signaling is sensitive Gyc76C, a peptide receptor that stimulates the production of cGMP in cells. We identify downstream intracellular effectors of this cGMP activity, but provide evidence that the effects on the BMP pathway are not mediated at the intracellular level, but rather through cGMP’s effects upon the extracellular matrix and matrix-remodeling proteinases, which in turn affects the activity of extracellular BMP-binding proteins. We discuss differences and parallels with other examples of cGMP activity in Drosophila melanogaster and mammals.

Shared mushroom body circuits underlie visual and olfactory memories in Drosophila

In nature, animals form memories associating reward or punishment with stimuli from different sensory modalities, such as smells and colors. It is unclear, however, how distinct sensory memories are processed in the brain. We established appetitive and aversive visual learning assays for Drosophila that are comparable to the widely used olfactory learning assays. These assays share critical features, such as reinforcing stimuli (sugar reward and electric shock punishment), and allow direct comparison of the cellular requirements for visual and olfactory memories. We found that the same subsets of dopamine neurons drive formation of both sensory memories. Furthermore, distinct yet partially overlapping subsets of mushroom body intrinsic neurons are required for visual and olfactory memories. Thus, our results suggest that distinct sensory memories are processed in a common brain center. Such centralization of related brain functions is an economical design that avoids the repetition of similar circuit motifs.

DOI:http://dx.doi.org/10.7554/eLife.02395.001

Animals tend to associate good and bad things with certain visual scenes, smells and other kinds of sensory information. If we get food poisoning after eating a new food, for example, we tend to associate the taste and smell of the new food with feelings of illness. This is an example of a negative ‘associative memory’, and it can persist for months, even when we know that our sickness was not caused by the new food itself but by some foreign body that should not have been in the food. The same is true for positive associative memories.

It is known that many associative memories contain information from more than one of the senses. Our memory of a favorite food, for instance, includes its scent, color and texture, as well as its taste. However, little is known about the ways in which information from the different senses is processed in the brain. Does each sense have its own dedicated memory circuit, or do multiple senses converge to the same memory circuit?

A number of studies have used olfactory (smell) and visual stimuli to study the basic neuroscience that underpins associative memories in fruit flies. The olfactory experiments traditionally use sugar and electric shocks to induce positive and negative associations with various scents. However, the visual experiments use other methods to induce associations with colors. This means that it is difficult to combine and compare the results of olfactory and visual experiments.

Now, Vogt, Schnaitmann et al. have developed a transparent grid that can be used to administer electric shocks in visual experiments. This allows direct comparisons to be made between the neuronal processing of visual associative memories and the neural processing of olfactory associative memories.

Vogt, Schnaitmann et al. showed that both visual and olfactory stimuli are modulated in the same subset of dopamine neurons for positive associative memories. Similarly, another subset of dopamine neurons was found to drive negative memories of both the visual and olfactory stimuli. The work of Vogt, Schnaitmann et al. shows that associative memories are processed by a centralized circuit that receives both visual and olfactory inputs, thus reducing the number of memory circuits needed for such memories.

DOI:http://dx.doi.org/10.7554/eLife.02395.002

Maggot learning and Synapsin function

Drosophila larvae are focused on feeding and have few neurons. Within these bounds, however, there still are behavioural degrees of freedom. This review is devoted to what these elements of flexibility are, and how they come about. Regarding odour-food associative learning, the emerging working hypothesis is that when a mushroom body neuron is activated as a part of an odour-specific set of mushroom body neurons, and coincidently receives a reinforcement signal carried by aminergic neurons, the AC-cAMP-PKA cascade is triggered. One substrate of this cascade is Synapsin, and therefore this review features a general and comparative discussion of Synapsin function. Phosphorylation of Synapsin ensures an alteration of synaptic strength between this mushroom body neuron and its target neuron(s). If the trained odour is encountered again, the pattern of mushroom body neurons coding this odour is activated, such that their modified output now allows conditioned behaviour. However, such an activated memory trace does not automatically cause conditioned behaviour. Rather, in a process that remains off-line from behaviour, the larvae compare the value of the testing situation (based on gustatory input) with the value of the odour-activated memory trace (based on mushroom body output). The circuit towards appetitive conditioned behaviour is closed only if the memory trace suggests that tracking down the learned odour will lead to a place better than the current one. It is this expectation of a positive outcome that is the immediate cause of appetitive conditioned behaviour. Such conditioned search for reward corresponds to a view of aversive conditioned behaviour as conditioned escape from punishment, which is enabled only if there is something to escape from - much in the same way as we only search for things that are not there, and run for the emergency exit only when there is an emergency. One may now ask whether beyond 'value' additional information about reinforcement is contained in the memory trace, such as information about the kind and intensity of the reinforcer used. The Drosophila larva may allow us to develop satisfyingly detailed accounts of such mnemonic richness - if it exists.

Parallel pathways for cross-modal memory retrieval in Drosophila

Memory-retrieval processing of cross-modal sensory preconditioning is vital for understanding the plasticity underlying the interactions between modalities. As part of the sensory preconditioning paradigm, it has been hypothesized that the conditioned response to an unreinforced cue depends on the memory of the reinforced cue via a sensory link between the two cues. To test this hypothesis, we studied cross-modal memory-retrieval processing in a genetically tractable model organism, Drosophila melanogaster. By expressing the dominant temperature-sensitive shibire(ts1) (shi(ts1)) transgene, which blocks synaptic vesicle recycling of specific neural subsets with the Gal4/UAS system at the restrictive temperature, we specifically blocked visual and olfactory memory retrieval, either alone or in combination; memory acquisition remained intact for these modalities. Blocking the memory retrieval of the reinforced olfactory cues did not impair the conditioned response to the unreinforced visual cues or vice versa, in contrast to the canonical memory-retrieval processing of sensory preconditioning. In addition, these conditioned responses can be abolished by blocking the memory retrieval of the two modalities simultaneously. In sum, our results indicated that a conditioned response to an unreinforced cue in cross-modal sensory preconditioning can be recalled through parallel pathways.

The propensity for consuming ethanol in Drosophila requires rutabaga adenylyl cyclase expression within mushroom body neurons

Alcohol activates reward systems through an unknown mechanism, in some cases leading to alcohol abuse and dependence. Herein, we utilized a two-choice Capillary Feeder assay to address the neural and molecular basis for ethanol self-administration in Drosophila melanogaster. Wild-type Drosophila shows a significant preference for food containing between 5% and 15% ethanol. Preferred ethanol self-administration does not appear to be due to caloric advantage, nor due to perceptual biases, suggesting a hedonic bias for ethanol exists in Drosophila. Interestingly, rutabaga adenylyl cyclase expression within intrinsic mushroom body neurons is necessary for robust ethanol self-administration. The expression of rutabaga in mushroom bodies is also required for both appetitive and aversive olfactory associative memories, suggesting that reinforced behavior has an important role in the ethanol self-administration in Drosophila. However, rutabaga expression is required more broadly within the mushroom bodies for the preference for ethanol-containing food than for olfactory memories reinforced by sugar reward. Together these data implicate cAMP signaling and behavioral reinforcement for preferred ethanol self-administration in D. melanogaster.

Mutations in NSUN2 cause autosomal-recessive intellectual disability

With a prevalence between 1 and 3%, hereditary forms of intellectual disability (ID) are among the most important problems in health care. Particularly, autosomal-recessive forms of the disorder have a very heterogeneous molecular basis, and genes with an increased number of disease-causing mutations are not common. Here, we report on three different mutations (two nonsense mutations, c.679C>T [p.Gln227(∗)] and c.1114C>T [p.Gln372(∗)], as well as one splicing mutation, g.6622224A>C [p.Ile179Argfs(∗)192]) that cause a loss of the tRNA-methyltransferase-encoding NSUN2 main transcript in homozygotes. We identified the mutations by sequencing exons and exon-intron boundaries within the genomic region where the linkage intervals of three independent consanguineous families of Iranian and Kurdish origin overlapped with the previously described MRT5 locus. In order to gain further evidence concerning the effect of a loss of NSUN2 on memory and learning, we constructed a Drosophila model by deleting the NSUN2 ortholog, CG6133, and investigated the mutants by using molecular and behavioral approaches. When the Drosophila melanogaster NSUN2 ortholog was deleted, severe short-term-memory (STM) deficits were observed; STM could be rescued by re-expression of the wild-type protein in the nervous system. The humans homozygous for NSUN2 mutations showed an overlapping phenotype consisting of moderate to severe ID and facial dysmorphism (which includes a long face, characteristic eyebrows, a long nose, and a small chin), suggesting that mutations in this gene might even induce a syndromic form of ID. Moreover, our observations from the Drosophila model point toward an evolutionarily conserved role of RNA methylation in normal cognitive development.

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 influence of natural variation at the foraging gene on thermotolerance in adult Drosophila in a narrow temperature range

Poikilothermic organisms such as insects have mechanisms to protect neural function under high temperature stress. Natural variation at the foraging (for) locus of the fruit fly, Drosophila melanogaster, encoding a cGMP-dependent protein kinase (PKG), influences neural thermotolerance in Drosophila larvae. The current study re-examines thermotolerance of adult flies to account for inconsistencies in the documented role of for during hyperthermia. We found that adult for (R) (rover) flies with high PKG activity were incapacitated faster under hyperthermic conditions of 39°C compared to their lower PKG activity counterparts for (s) and for (s2) (sitters), but not at higher temperatures. This indicates that lowered PKG activity promotes tolerance to heat stress, and that the for gene influences thermotolerance for a narrow range of temperatures in adult flies.

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 aru^8–128 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.

Lack of prediction for high-temperature exposures enhances Drosophila place learning

Animals receive rewards and punishments in different patterns. Sometimes stimuli or behaviors can become predictors of future good or bad events. Through learning, experienced animals can then avoid new but similar bad situations, or actively seek those conditions that give rise to good results. Not all good or bad events, however, can be accurately predicted. Interestingly, unpredicted exposure to presumed rewards or punishments can inhibit or enhance later learning, thus linking the two types of experiences. In Drosophila, place memories can be readily formed; indeed, memory was enhanced by exposing flies to high temperatures that are unpaired from place or behavioral contingencies. Whether it is the exposure to high temperatures per se or the lack of prediction about the exposure that is crucial for memory enhancement is unknown. Through yoking experiments, we show that the uncertainty about exposure to high temperatures positively biases later place memory. However, the unpredicted exposures to high temperature do not alter thermosensitivity. Thus, the uncertainty bias does not alter thermosensory processes. An unidentified system is proposed to buffer the high-temperature reinforcement information to influence place learning when accurate predictions can be identified.

Learning and memory in Drosophila: behavior, genetics, and neural systems

The rich behavioral repertoire that Drosophila use to navigate in their natural environment suggests that flies can use memories to inform decisions. Development of paradigms to examine memories that restrict behavioral choice was essential in furthering our understanding of the genetics and neural systems of memory formation in the fly. Olfactory, visual, and place memory paradigms have proven influential in determining principles for the mechanisms of memory formation. Several parts of the nervous system have been shown to be important for different types of memories, including the mushroom bodies and the central complex. Thus far, about 40 genes have been linked to normal olfactory short-term memory. A subset of these genes have also been tested for a role in visual and place memory. Some genes have a common function in memory formation, specificity of action comes from where in the nervous system these genes act. Alternatively, some genes have a more restricted role in different types of memories.