J. Douglas Armstrong

A Neural Circuit Mechanism Integrating Motivational State with Memory Expression in Drosophila

Behavioral expression of food-associated memory in fruit flies is constrained by satiety and promoted by hunger, suggesting an influence of motivational state. Here, we identify a neural mechanism that integrates the internal state of hunger and appetitive memory. We show that stimulation of neurons that express neuropeptide F (dNPF), an ortholog of mammalian NPY, mimics food deprivation and promotes memory performance in satiated flies. Robust appetitive memory performance requires the dNPF receptor in six dopaminergic neurons that innervate a distinct region of the mushroom bodies. Blocking these dopaminergic neurons releases memory performance in satiated flies, whereas stimulation suppresses memory performance in hungry flies. Therefore, dNPF and dopamine provide a motivational switch in the mushroom body that controls the output of appetitive memory.

Subdivision of the drosophila mushroom bodies by enhancer-trap expression patterns

Phylogenetically conserved brain centers known as mushroom bodies are implicated in insect associative learning and in several other aspects of insect behavior. Kenyon cells, the intrinsic neurons of mushroom bodies, have been generally considered to be disposed as homogenous arrays. Such a simple picture imposes constraints on interpreting the diverse behavioral and computational properties that mushroom bodies are supposed to perform. Using a P[GAL4] enhancer-trap approach, we have revealed axonal processes corresponding to intrinsic cells of the Drosophila mushroom bodies. Rather than being homogenous, we find the Drosophila mushroom bodies to be compound neuropils in which parallel subcomponents exhibit discrete patterns of gene expression. Different patterns correspond to hitherto unobserved differences in Kenyon cell trajectory and placement. On the basis of this unexpected complexity, we propose a model for mushroom body function in which parallel channels of information flow, perhaps with different computational properties, subserve different behavioral roles.

Simple Neurite Tracer

MOTIVATION Advances in techniques to sparsely label neurons unlock the potential to reconstruct connectivity from 3D image stacks acquired by light microscopy. We present an application for semi-automated tracing of neurons to quickly annotate noisy datasets and construct complex neuronal topologies, which we call the Simple Neurite Tracer. AVAILABILITY Simple Neurite Tracer is open source software, licensed under the GNU General Public Licence (GPL) and based on the public domain image processing software ImageJ. The software and further documentation are available via http://fiji.sc/Simple_Neurite_Tracer as part of the package Fiji, and can be used on Windows, Mac OS and Linux. Documentation and introductory screencasts are available at the same URL. CONTACT longair@ini.phys.ethz.ch; longair@ini.phys.ethz.ch.

The amnesiac gene product is expressed in two neurons in the Drosophila brain that are critical for memory.

Mutations in the amnesiac gene in Drosophila affect both memory retention and ethanol sensitivity. The predicted amnesiac gene product, AMN, is an apparent preproneuropeptide, and previous studies suggest that it stimulates cAMP synthesis. Here we show that, unlike other learning-related Drosophila proteins, AMN is not preferentially expressed in mushroom bodies. Instead, it is strongly expressed in two large neurons that project over all the lobes of the mushroom bodies, a finding that suggests a modulatory role for AMN in memory formation. Genetically engineered blockade of vesicle recycling in these cells abbreviates memory as in the amnesiac mutant. Moreover, restoration of amn gene expression to these cells reestablishes normal olfactory memory in an amn deletion background. These results indicate that AMN neuropeptide release onto the mushroom bodies is critical for normal olfactory memory.

A Systematic Nomenclature for the Insect Brain

Despite the importance of the insect nervous system for functional and developmental neuroscience, descriptions of insect brains have suffered from a lack of uniform nomenclature. Ambiguous definitions of brain regions and fiber bundles have contributed to the variation of names used to describe the same structure. The lack of clearly determined neuropil boundaries has made it difficult to document precise locations of neuronal projections for connectomics study. To address such issues, a consortium of neurobiologists studying arthropod brains, the Insect Brain Name Working Group, has established the present hierarchical nomenclature system, using the brain of Drosophila melanogaster as the reference framework, while taking the brains of other taxa into careful consideration for maximum consistency and expandability. The following summarizes the consortiums nomenclature system and highlights examples of existing ambiguities and remedies for them. This nomenclature is intended to serve as a standard of reference for the study of the brain of Drosophila and other insects.

Targeted tandem affinity purification of PSD-95 recovers core postsynaptic complexes and schizophrenia susceptibility proteins

The molecular complexity of mammalian proteomes demands new methods for mapping the organization of multiprotein complexes. Here, we combine mouse genetics and proteomics to characterize synapse protein complexes and interaction networks. New tandem affinity purification (TAP) tags were fused to the carboxyl terminus of PSD‐95 using gene targeting in mice. Homozygous mice showed no detectable abnormalities in PSD‐95 expression, subcellular localization or synaptic electrophysiological function. Analysis of multiprotein complexes purified under native conditions by mass spectrometry defined known and new interactors: 118 proteins comprising crucial functional components of synapses, including glutamate receptors, K+ channels, scaffolding and signaling proteins, were recovered. Network clustering of protein interactions generated five connected clusters, with two clusters containing all the major ionotropic glutamate receptors and one cluster with voltage‐dependent K+ channels. Annotation of clusters with human disease associations revealed that multiple disorders map to the network, with a significant correlation of schizophrenia within the glutamate receptor clusters. This targeted TAP tagging strategy is generally applicable to mammalian proteomics and systems biology approaches to disease.

Genetic analysis of the Drosophila ellipsoid body neuropil: Organization and development of the central complex

The central complex is an important center for higher-order brain function in insects. It is an intricate neuropil composed of four substructures. Each substructure contains repeated neuronal elements which are connected by processes such that topography is maintained. Although the neuronal architecture has been described in several insects and the behavioral role investigated in various experiments, the exact function of this neuropil has proven elusive. To describe the architecture of the central complex, we study 15 enhancer-trap lines that label various ellipsoid body neuron types. We find evidence for restriction of gene expression that is correlated with specific neuronal types: such correlations suggest functional classifications as well. We show that some enhancer-trap patterns reveal a single ellipsoid body neuron type, while others label multiple types. We describe the development of the ellipsoid body neuropil in wild-type animals and propose developmental mechanisms based on animals displaying structural mutations of this neuropil. The experiments performed here demonstrate the degree of resolution possible from the analysis of enhancer-trap lines and form a useful library of tools for future structure/function studies of the ellipsoid body.

Evolutionary expansion and anatomical specialization of synapse proteome complexity

Understanding the origins and evolution of synapses may provide insight into species diversity and the organization of the brain. Using comparative proteomics and genomics, we examined the evolution of the postsynaptic density (PSD) and membrane-associated guanylate kinase (MAGUK)-associated signaling complexes (MASCs) that underlie learning and memory. PSD and MASC orthologs found in yeast carry out basic cellular functions to regulate protein synthesis and structural plasticity. We observed marked changes in signaling complexity at the yeast-metazoan and invertebrate-vertebrate boundaries, with an expansion of key synaptic components, notably receptors, adhesion/cytoskeletal proteins and scaffold proteins. A proteomic comparison of Drosophila and mouse MASCs revealed species-specific adaptation with greater signaling complexity in mouse. Although synaptic components were conserved amongst diverse vertebrate species, mapping mRNA and protein expression in the mouse brain showed that vertebrate-specific components preferentially contributed to differences between brain regions. We propose that the evolution of synapse complexity around a core proto-synapse has contributed to invertebrate-vertebrate differences and to brain specialization.

Functional dissection of the drosophila mushroom bodies by selective feminization ofagenetically defined subcompartments

Relatively little is known about the neural circuitry underlying sex-specific behaviors. We have expressed the feminizing gene transformer in genetically defined subregions of the brain of male Drosophila, and in particular within different domains of the mushroom bodies. Mushroom bodies are phylogenetically conserved insect brain centers implicated in associative learning and various other aspects of behavior. Expression of transformer in lines that mark certain subsets of mushroom body intrinsic neurons, and in a line that marks a component of the antennal lobe, causes males to exhibit nondiscriminatory sexual behavior: they court mature males in addition to females. Expression of transformer in other mushroom body domains, and in control lines, has no such effect. Our data support the view that genetically defined subsets of mushroom body intrinsic neurons perform different functional roles.

The proteomes of neurotransmitter receptor complexes form modular networks with distributed functionality underlying plasticity and behaviour

Neuronal synapses play fundamental roles in information processing, behaviour and disease. Neurotransmitter receptor complexes, such as the mammalian N‐methyl‐D‐aspartate receptor complex (NRC/MASC) comprising 186 proteins, are major components of the synapse proteome. Here we investigate the organisation and function of NRC/MASC using a systems biology approach. Systematic annotation showed that the complex contained proteins implicated in a wide range of cognitive processes, synaptic plasticity and psychiatric diseases. Protein domains were evolutionarily conserved from yeast, but enriched with signalling domains associated with the emergence of multicellularity. Mapping of protein–protein interactions to create a network representation of the complex revealed that simple principles underlie the functional organisation of both proteins and their clusters, with modularity reflecting functional specialisation. The known functional roles of NRC/MASC proteins suggest the complex co‐ordinates signalling to diverse effector pathways underlying neuronal plasticity. Importantly, using quantitative data from synaptic plasticity experiments, our model correctly predicts robustness to mutations and drug interference. These studies of synapse proteome organisation suggest that molecular networks with simple design principles underpin synaptic signalling properties with important roles in physiology, behaviour and disease.