@article {5686, title = {The Drosophila larval visual system: high-resolution analysis of a simple visual neuropil.}, journal = {Developmental Biology}, volume = {358}, year = {2011}, month = {2011 Oct 1}, pages = {33-43}, abstract = {

The task of the visual system is to translate light into neuronal encoded information. This translation of photons into neuronal signals is achieved by photoreceptor neurons (PRs), specialized sensory neurons, located in the eye. Upon perception of light the PRs will send a signal to target neurons, which represent a first station of visual processing. Increasing complexity of visual processing stems from the number of distinct PR subtypes and their various types of target neurons that are contacted. The visual system of the fruit fly larva represents a simple visual system (larval optic neuropil, LON) that consists of 12 PRs falling into two classes: blue-senstive PRs expressing Rhodopsin 5 (Rh5) and green-sensitive PRs expressing Rhodopsin 6 (Rh6). These afferents contact a small number of target neurons, including optic lobe pioneers (OLPs) and lateral clock neurons (LNs). We combine the use of genetic markers to label both PR subtypes and the distinct, identifiable sets of target neurons with a serial EM reconstruction to generate a high-resolution map of the larval optic neuropil. We find that the larval optic neuropil shows a clear bipartite organization consisting of one domain innervated by PRs and one devoid of PR axons. The topology of PR projections, in particular the relationship between Rh5 and Rh6 afferents, is maintained from the nerve entering the brain to the axon terminals. The target neurons can be subdivided according to neurotransmitter or neuropeptide they use as well as the location within the brain. We further track the larval optic neuropil through development from first larval instar to its location in the adult brain as the accessory medulla.

}, keywords = {Animals, Confocal, Drosophila, Drosophila Proteins, Electron, Immunohistochemistry, Invertebrate, Larva, Microscopy, Neuropil, Ocular, Photoreceptor Cells, Rhodopsin, Synapses, Transmission, Vision}, issn = {1095-564X}, doi = {10.1016/j.ydbio.2011.07.006}, author = {Sprecher, Simon G and Cardona, Albert and Hartenstein, Volker.} } @article {5689, title = {Identifying neuronal lineages of Drosophila by sequence analysis of axon tracts.}, journal = {The Journal of Neuroscience}, volume = {30}, year = {2010}, month = {2010 Jun 2}, pages = {7538-53}, abstract = {

The Drosophila brain is formed by an invariant set of lineages, each of which is derived from a unique neural stem cell (neuroblast) and forms a genetic and structural unit of the brain. The task of reconstructing brain circuitry at the level of individual neurons can be made significantly easier by assigning neurons to their respective lineages. In this article we address the automation of neuron and lineage identification. We focused on the Drosophila brain lineages at the larval stage when they form easily recognizable secondary axon tracts (SATs) that were previously partially characterized. We now generated an annotated digital database containing all lineage tracts reconstructed from five registered wild-type brains, at higher resolution and including some that were previously not characterized. We developed a method for SAT structural comparisons based on a dynamic programming approach akin to nucleotide sequence alignment and a machine learning classifier trained on the annotated database of reference SATs. We quantified the stereotypy of SATs by measuring the residual variability of aligned wild-type SATs. Next, we used our method for the identification of SATs within wild-type larval brains, and found it highly accurate (93-99\%). The method proved highly robust for the identification of lineages in mutant brains and in brains that differed in developmental time or labeling. We describe for the first time an algorithm that quantifies neuronal projection stereotypy in the Drosophila brain and use the algorithm for automatic neuron and lineage recognition.

}, keywords = {Algorithms, Animals, Automatic Data Processing, Axons, Brain, Brain Mapping, Caspase 3, Cell Lineage, Computer-Assisted, Confocal, Dendrites, Drosophila, Drosophila Proteins, Embryo, Genetically Modified, Green Fluorescent Proteins, Image Processing, Microscopy, Models, Neurological, Neurons, Nonmammalian, Reproducibility of Results, Software}, issn = {1529-2401}, doi = {10.1523/JNEUROSCI.0186-10.2010}, author = {Cardona, Albert and Saalfeld, Stephan and Arganda, Ignacio and Pereanu, Wayne and Schindelin, Johannes and Hartenstein, Volker.} } @article {5687, title = {An integrated micro- and macroarchitectural analysis of the Drosophila brain by computer-assisted serial section electron microscopy.}, journal = {PLoS Biology}, volume = {8}, year = {2010}, month = {2010}, abstract = {

The analysis of microcircuitry (the connectivity at the level of individual neuronal processes and synapses), which is indispensable for our understanding of brain function, is based on serial transmission electron microscopy (TEM) or one of its modern variants. Due to technical limitations, most previous studies that used serial TEM recorded relatively small stacks of individual neurons. As a result, our knowledge of microcircuitry in any nervous system is very limited. We applied the software package TrakEM2 to reconstruct neuronal microcircuitry from TEM sections of a small brain, the early larval brain of Drosophila melanogaster. TrakEM2 enables us to embed the analysis of the TEM image volumes at the microcircuit level into a light microscopically derived neuro-anatomical framework, by registering confocal stacks containing sparsely labeled neural structures with the TEM image volume. We imaged two sets of serial TEM sections of the Drosophila first instar larval brain neuropile and one ventral nerve cord segment, and here report our first results pertaining to Drosophila brain microcircuitry. Terminal neurites fall into a small number of generic classes termed globular, varicose, axiform, and dendritiform. Globular and varicose neurites have large diameter segments that carry almost exclusively presynaptic sites. Dendritiform neurites are thin, highly branched processes that are almost exclusively postsynaptic. Due to the high branching density of dendritiform fibers and the fact that synapses are polyadic, neurites are highly interconnected even within small neuropile volumes. We describe the network motifs most frequently encountered in the Drosophila neuropile. Our study introduces an approach towards a comprehensive anatomical reconstruction of neuronal microcircuitry and delivers microcircuitry comparisons between vertebrate and insect neuropile.

}, keywords = {Animals, Brain, Computer-Assisted, Drosophila melanogaster, Electron, Humans, Image Processing, Imaging, Microscopy, Neurons, Neuropil, Software, Synapses, Three-Dimensional, Transmission}, issn = {1545-7885}, doi = {10.1371/journal.pbio.1000502}, author = {Cardona, Albert and Saalfeld, Stephan and Preibisch, Stephan and Schmid, Benjamin and Cheng, Anchi and Pulokas, Jim and Tomancak, Pavel and Hartenstein, Volker.} } @article {5688, title = {Structure of the central nervous system of a juvenile acoel, Symsagittifera roscoffensis.}, journal = {Development Genes \& Evolution}, volume = {220}, year = {2010}, month = {2010 Sep}, pages = {61-76}, abstract = {

The neuroarchitecture of Acoela has been at the center of morphological debates. Some authors, using immunochemical tools, suggest that the nervous system in Acoela is organized as a commissural brain that bears little resemblance to the central, ganglionic type brain of other flatworms, and bilaterians in general. Others, who used histological staining on paraffin sections, conclude that it is a compact structure (an endonal brain; e.g., Raikova 2004; von Graff 1891; Delage Arch Zool Exp G{\'e}n 4:109-144, 1886). To address this question with modern tools, we have obtained images from serial transmission electron microscopic sections of the entire hatchling of Symsagittifera roscoffensis. In addition, we obtained data from wholemounts of hatchlings labeled with markers for serotonin and tyrosinated tubulin. Our data show that the central nervous system of a juvenile S. roscoffensis consists of an anterior compact brain, formed by a dense, bilobed mass of neuronal cell bodies surrounding a central neuropile. The neuropile flanks the median statocyst and contains several types of neurites, classified according to their types of synaptic vesicles. The neuropile issues three pairs of nerve cords that run at different dorso-ventral positions along the whole length of the body. Neuronal cell bodies flank the cords, and neuromuscular synapses are abundant. The TEM analysis also reveals different classes of peripheral sensory neurons and provides valuable information about the spatial relationships between neurites and other cell types within the brain and nerve cords. We conclude that the acoel S. roscoffensis has a central brain that is comparable in size and architecture to the brain of other (rhabditophoran) flatworms.

}, keywords = {Anatomic, Animals, Brain, Central Nervous System, Electron, Imaging, Microscopy, Models, Muscles, Nerve Fibers, Nerve Net, Neurites, Neuropil, Platyhelminths, Sensory Receptor Cells, Synapses, Three-Dimensional, Transmission}, issn = {1432-041X}, doi = {10.1007/s00427-010-0328-2}, author = {Bery, Amandine and Cardona, Albert and Martinez, Pedro and Hartenstein, Volker.} } @article {5693, title = {Neuronal fiber tracts connecting the brain and ventral nerve cord of the early Drosophila larva.}, journal = {The Journal of Comparative Neurology}, volume = {515}, year = {2009}, month = {2009 Aug 1}, pages = {427-40}, abstract = {

By using a combination of dye injections, clonal labeling, and molecular markers, we have reconstructed the axonal connections between brain and ventral nerve cord of the first-instar Drosophila larva. Out of the approximately 1,400 neurons that form the early larval brain hemisphere, less than 50 cells have axons descending into the ventral nerve cord. Descending neurons fall into four topologically defined clusters located in the anteromedial, anterolateral, dorsal, and basoposterior brain, respectively. The anterolateral cluster represents a lineage derived from a single neuroblast. Terminations of descending neurons are almost exclusively found in the anterior part of the ventral nerve cord, represented by the gnathal and thoracic neuromeres. This region also contains small numbers of neurons with axons ascending into the brain. Terminals of the ascending axons are found in the same basal brain regions that also contain descending neurons. We have mapped ascending and descending axons to the previously described scaffold of longitudinal fiber tracts that interconnect different neuromeres of the ventral nerve cord and the brain. This work provides a structural framework for functional and genetic studies addressing the control of Drosophila larval behavior by brain circuits.

}, keywords = {Animals, Brain, Cell Count, Drosophila, Drosophila Proteins, Ganglia, Genetically Modified, Green Fluorescent Proteins, Imaging, Invertebrate, Larva, Models, Neural Pathways, Neurological, Neurons, Spinal Cord, Three-Dimensional}, issn = {1096-9861}, doi = {10.1002/cne.22086}, author = {Cardona, Albert and Larsen, Camilla and Hartenstein, Volker.} }