Neuroanatomy: Decoding the Fly Brain

SummaryDespite their relatively small brains, with only about 100,000 neurons, fruit flies show many complex behaviours. Understanding how these behaviours are generated will require a wiring diagram of the brain, and significant progress is being made towards this goal. One study has labelled 16,000 individual neurons and generated a coarse wiring diagram of the whole fly brain, identifying subnetworks that may carry out local information processing

NeuroAnatomy Toolbox v1.5.2

<p>nat v1.5.2</p> <p>This is the current stable release on github. Changes since the last stable release on CRAN (v1.4.10) are detailed below.</p> <p>Changes in version 1.5.2:</p> <ul> <li>add seglengths function for neurons</li> <li>add segmentgraph function to produced a simplified graph representation of neurons with one edge per segment</li> <li>add potential_synapses.dotprops method</li> <li>add as.seglist.neuron method</li> <li>teach plot3d.hxsurf and subset.hxsurf to accept regexes</li> <li>always drop unused vertices in as.mesh3d.hxsurf</li> <li>fix bug in write.neurons when subdir not specified</li> <li>fix colouring of vectors by plot3d.dotprops</li> <li>dev: switch to roxygygen2 v4</li> </ul> <p>Changes in version 1.5.1:</p> <ul> <li>add potential_synapses (from nat.as)</li> <li>surfaces: add subset.hxsurf and as.mesh3d</li> <li>Teach read.im3d to read Vaa3d raw format</li> <li>add plot.neuronlist (for 2d plotting)</li> <li>add c.neuronlist function to combine neuronlists</li> <li>add db argument to plot3d.character</li> <li>make WithNodes=FALSE the default for plot3d.neuronlist</li> <li>make asp=1 the default for image.im3d</li> <li>write.cmtkreg warns if versions specified by cmtkreg attribute and argument differ (to avoid writing old registrations as if they were new or vice versa)</li> <li>fix: prune.neuronlist method signature (and therefore dispatch)</li> </ul

IBNWB Template Brain

<p>An extended, whole-brain version of the original IBN template brain made available from:</p> <p><strong>A Systematic Nomenclature for the Insect Brain</strong><br> Kei Ito, Kazunori Shinomiya, Masayoshi Ito, J. Douglas Armstrong, George Boyan, Volker Hartenstein, Steffen Harzsch, Martin Heisenberg, Uwe Homberg, Arnim Jenett, Haig Keshishian, Linda L. Restifo, Wolfgang Rössler, Julie H. Simpson, Nicholas J. Strausfeld, Roland Strauss, Leslie B. Vosshall, Insect Brain Name Working Group<br> http://dx.doi.org/10.1016/j.neuron.2013.12.017</p> <p>The green channel (n-syb-GFP) of the tricolour confocal data provided was taken, duplicated and flipped about the medio-lateral axis using Fiji. The Fiji plugin 'Pairwise stitching' was used to stitch the two stacks together with an offset of 392 pixels. This offset was chosen by eye as the one from the range of offsets 385–400 pixels that produced the most anatomically correct result. The overlapping region's intensity was set using the 'linear blend' method.</p

Glomerular Maps without Cellular Redundancy at Successive Levels of the Drosophila Larval Olfactory CircuitGlomerular Maps without Cellular Redundancy at Successive Levels of the Drosophila Larval Olfactory Circuit

Background: Drosophila larvae possess only 21 odorant-receptor neurons (ORNs), whereas adults have 1,300. Does this suggest that the larval olfactory system is built according to a different design than its adult counterpart, or is it just a miniature version thereof? Results: By genetically labeling single neurons with FLP-out and MARCM techniques, we analyze the connectivity of the larval olfactory circuit. We show that each of the 21 ORNs is unique and projects to one of 21 morphologically identifiable antennal-lobe glomeruli. Each glomerulus seems to be innervated by a single projection neuron. Each projection neuron sends its axon to one or two of about 28 glomeruli in the mushroom-body calyx. We have discovered at least seven types of projection neurons that stereotypically link an identified antennal-lobe glomerulus with an identified calycal glomerulus and thus create an olfactory map in a higher brain center. Conclusions: The basic design of the larval olfactory system is similar to the adult one. However, ORNs and projection neurons lack cellular redundancy and do not exhibit any convergent or divergent connectivity; 21 ORNs confront essentially similar numbers of antennal-lobe glomeruli, projection neurons, and calycal glomeruli. Hence, we propose the Drosophila larva as an “elementary” olfactory model system

Representation of the Glomerular Olfactory Map in the Drosophila Brain

AbstractWe explored how the odor map in the Drosophila antennal lobe is represented in higher olfactory centers, the mushroom body and lateral horn. Systematic single-cell tracing of projection neurons (PNs) that send dendrites to specific glomeruli in the antennal lobe revealed their stereotypical axon branching patterns and terminal fields in the lateral horn. PNs with similar axon terminal fields tend to receive input from neighboring glomeruli. The glomerular classes of individual PNs could be accurately predicted based solely on their axon projection patterns. The sum of these patterns defines an “axon map” in higher olfactory centers reflecting which olfactory receptors provide input. This map is characterized by spatial convergence and divergence of PN axons, allowing integration of olfactory information

Cellular Organization of the Neural Circuit that Drives Drosophila Courtship Behavior

SummaryBackgroundCourtship behavior in Drosophila has been causally linked to the activity of the heterogeneous set of ∼1500 neurons that express the sex-specific transcripts of the fruitless (fru) gene, but we currently lack an appreciation of the cellular diversity within this population, the extent to which these cells are sexually dimorphic, and how they might be organized into functional circuits.ResultsWe used genetic methods to define 100 distinct classes of fru neuron, which we compiled into a digital 3D atlas at cellular resolution. We determined the polarity of many of these neurons and computed their likely patterns of connectivity, thereby assembling them into a neural circuit that extends from sensory input to motor output. The cellular organization of this circuit reveals neuronal pathways in the brain that are likely to integrate multiple sensory cues from other flies and to issue descending control signals to motor circuits in the thoracic ganglia. We identified 11 anatomical dimorphisms within this circuit: neurons that are male specific, are more numerous in males than females, or have distinct arborization patterns in males and females.ConclusionsThe cellular organization of the fru circuit suggests how multiple distinct sensory cues are integrated in the fly's brain to drive sex-specific courtship behavior. We propose that sensory processing and motor control are mediated through circuits that are largely similar in males and females. Sex-specific behavior may instead arise through dimorphic circuits in the brain and nerve cord that differentially couple sensory input to motor output

Olfactory Neurons and Brain Centers Directing Oviposition Decisions in Drosophila

Summary: The sense of smell influences many behaviors, yet how odors are represented in the brain remains unclear. A major challenge to studying olfaction is the lack of methods allowing activation of specific types of olfactory neurons in an ethologically relevant setting. To address this, we developed a genetic method in Drosophila called olfactogenetics in which a narrowly tuned odorant receptor, Or56a, is ectopically expressed in different olfactory neuron types. Stimulation with geosmin (the only known Or56a ligand) in an Or56a mutant background leads to specific activation of only target olfactory neuron types. We used this approach to identify olfactory sensory neurons (OSNs) that directly guide oviposition decisions. We identify 5 OSN-types (Or71a, Or47b, Or49a, Or67b, and Or7a) that, when activated alone, suppress oviposition. Projection neurons partnering with these OSNs share a region of innervation in the lateral horn, suggesting that oviposition site selection might be encoded in this brain region. : Linking olfactory neurons to discrete behaviors is challenging. To address this, Chin et al. develop a genetic method in Drosophila that uses an odor to selectively activate different olfactory neurons. From a behavioral screen, they identify olfactory neurons and brain regions that might underlie aversive egg-laying decisions. Keywords: olfaction, oviposition, olfactory, olfactogenetics, geosmin, vinegar fly, genetics, genetic technique, odorant receptors, projection neuron