Reconstruction of Virtual Neural Circuits in an Insect Brain

The reconstruction of large-scale nervous systems represents a major scientific and engineering challenge in current neuroscience research that needs to be resolved in order to understand the emergent properties of such systems. We focus on insect nervous systems because they represent a good compromise between architectural simplicity and the ability to generate a rich behavioral repertoire. In insects, several sensory maps have been reconstructed so far. We provide an overview over this work including our reconstruction of population activity in the primary olfactory network, the antennal lobe. Our reconstruction approach, that also provides functional connectivity data, will be refined and extended to allow the building of larger scale neural circuits up to entire insect brains, from sensory input to motor output

Development of a Scheme and Tools to Construct a Standard Moth Brain for Neural Network Simulations

Understanding the neural mechanisms for sensing environmental information and controlling behavior in natural environments is a principal aim in neuroscience. One approach towards this goal is rebuilding neural systems by simulation. Despite their relatively simple brains compared with those of mammals, insects are capable of processing various sensory signals and generating adaptive behavior. Nevertheless, our global understanding at network system level is limited by experimental constraints. Simulations are very effective for investigating neural mechanisms when integrating both experimental data and hypotheses. However, it is still very difficult to construct a computational model at the whole brain level owing to the enormous number and complexity of the neurons. We focus on a unique behavior of the silkmoth to investigate neural mechanisms of sensory processing and behavioral control. Standard brains are used to consolidate experimental results and generate new insights through integration. In this study, we constructed a silkmoth standard brain and brain image, in which we registered segmented neuropil regions and neurons. Our original software tools for segmentation of neurons from confocal images, KNEWRiTE, and the registration module for segmented data, NeuroRegister, are shown to be very effective in neuronal registration for computational neuroscience studies

Odorant Concentration Differentiator for Intermittent Olfactory Signals

Animals need to discriminate differences in spatiotemporally distributed sensory signals in terms of quality as well as quantity for generating adaptive behavior. Olfactory signals characterized by odor identity and concentration are intermittently distributed in the environment. From these intervals of stimulation, animals process odorant concentration to localize partners or food sources. Although concentration–response characteristics in olfactory neurons have traditionally been investigated using single stimulus pulses, their behavior under intermittent stimulus regimens remains largely elusive. Using the silkmoth (Bombyx mori) pheromone processing system, a simple and behaviorally well-defined model for olfaction, we investigated the neuronal representation of odorant concentration upon intermittent stimulation in the naturally occurring range. To the first stimulus in a series, the responses of antennal lobe (AL) projection neurons (PNs) showed a concentration dependence as previously shown in many olfactory systems. However, PN response amplitudes dynamically changed upon exposure to intermittent stimuli of the same odorant concentration and settled to a constant, largely concentration-independent level. As a result, PN responses emphasized odorant concentration changes rather than encoding absolute concentration in pulse trains of stimuli. Olfactory receptor neurons did not contribute to this response transformation which was due to long-lasting inhibition affecting PNs in the AL. Simulations confirmed that inhibition also provides advantages when stimuli have naturalistic properties. The primary olfactory center thus functions as an odorant concentration differentiator to efficiently detect concentration changes, thereby improving odorant source orientation over a wide concentration range.UTokyo Research掲載「匂いの濃度を効率的に表現する脳の計算メカニズムの発見」 URI: http://www.u-tokyo.ac.jp/ja/utokyo-research/research-news/a-novel-neuronal-mechanism-to-efficiently-code-odorant-concentration/UTokyo Research "A novel neuronal mechanism to efficiently code odorant concentration" URI: http://www.u-tokyo.ac.jp/en/utokyo-research/research-news/a-novel-neuronal-mechanism-to-efficiently-code-odorant-concentration

Postsynaptic Odorant Concentration Dependent Inhibition Controls Temporal Properties of Spike Responses of Projection Neurons in the Moth Antennal Lobe

<div><p>Although odorant concentration-response characteristics of olfactory neurons have been widely investigated in a variety of animal species, the effect of odorant concentration on neural processing at circuit level is still poorly understood. Using calcium imaging in the silkmoth (<i>Bombyx mori</i>) pheromone processing circuit of the antennal lobe (AL), we studied the effect of odorant concentration on second-order projection neuron (PN) responses. While PN calcium responses of dendrites showed monotonic increases with odorant concentration, calcium responses of somata showed decreased responses at higher odorant concentrations due to postsynaptic inhibition. Simultaneous calcium imaging and electrophysiology revealed that calcium responses of PN somata but not dendrites reflect spiking activity. Inhibition shortened spike response duration rather than decreasing peak instantaneous spike frequency (ISF). Local interneurons (LNs) that were specifically activated at high odorant concentrations at which PN responses were suppressed are the putative source of inhibition. Our results imply the existence of an intraglomerular mechanism that preserves time resolution in olfactory processing over a wide odorant concentration range.</p></div

Inhibition Controls Temporal Properties of Spike Responses of Projection Neurons in the Moth Antennal Lobe

Fujiwara T, Kazawa T, Haupt S, Kanzaki R. Inhibition Controls Temporal Properties of Spike Responses of Projection Neurons in the Moth Antennal Lobe. PLOS ONE. 2014;9(2):Online-Ressource.{Although odorant concentration-response characteristics of olfactory neurons have been widely investigated in a variety of animal species, the effect of odorant concentration on neural processing at circuit level is still poorly understood. Using calcium imaging in the silkmoth (Bombyx mori) pheromone processing circuit of the antennal lobe (AL), we studied the effect of odorant concentration on second-order projection neuron (PN) responses. While PN calcium responses of dendrites showed monotonic increases with odorant concentration, calcium responses of somata showed decreased responses at higher odorant concentrations due to postsynaptic inhibition. Simultaneous calcium imaging and electrophysiology revealed that calcium responses of PN somata but not dendrites reflect spiking activity. Inhibition shortened spike response duration rather than decreasing peak instantaneous spike frequency (ISF). Local interneurons (LNs) that were specifically activated at high odorant concentrations at which PN responses were suppressed are the putative source of inhibition. Our results imply the existence of an intraglomerular mechanism that preserves time resolution in olfactory processing over a wide odorant concentration range.

Different concentration-response characteristics in dendrites and somata of antennal lobe (AL) projection neurons (PNs).

<p><b>A,</b> Schematic diagram of loading a calcium indicator into PNs with a micropipette by local electroporation (left). The toroid glomerulus processing bombykol is delineated by a dashed line. Fluorescence images of labeled PNs (middle) and the response to 1000 ng bombykol in false colors (right) are shown. Dendritic and somatic regions of interest (ROIs) are indicated by boxes. D: dorsal, M: medial. Scale bar: 50 µm. <b>B,</b> Representative time courses of PN responses to bombykol stimuli in the dendrites (left) and a soma (right). Black bars under time courses indicate the stimulus. <b>C,</b> Concentration-response characteristics of PN dendrites (magenta) and somata (green). Calcium responses were integrated over 3 s from stimulus onset. (P<0.05 for significant differences indicated by different letters associated with the data groups shown as means±SEM, n = 6 for dendrites and n = 17 for somata, one-way repeated measures ANOVA followed by Tukey-Kramer test).</p

Concentration-response characteristics of PNs under picrotoxin (PTX) treatment.

<p><b>A,</b> Representative time courses of PN responses to bombykol stimuli in the dendrites (left) and a soma (right) under PTX treatment. Black bars under time courses indicate stimulus. <b>B,</b> Concentration-response characteristics in PN dendrites (left) and somata (right) before (black) and under PTX treatment (magenta). Calcium responses were integrated over 3 s following stimulus onset (P<0.05 for significant differences indicated by different letters associated with the data groups shown as means±SEM, n = 6 at dendrites and n = 17 at somata, one-way repeated measures ANOVA followed by Tukey-Kramer test).</p

Calcium responses of local interneurons (LNs) to bombykol stimuli.

<p><b>A,</b> Schematic diagram of loading the calcium indicator into LNs with a micropipette by local electroporation. The toroid glomerulus is delineated by a dashed line. <b>B,</b> Two-dimensional projection of confocal sections (left, extending over 180 µm from the AL surface) and a single confocal optical section (middle) of labeled LNs. Scale bars: 100 µm. The arrowhead in the projection image indicates the injection site. LN branches innervating the MGC are resolved in the optical section. Stack projection images of the medial cell cluster (MC, right, top, extending over 60 µm in depth) and the lateral cell cluster (LC, right, bottom, extending over 60 µm in depth) are enlarged. Brightness and contrast of the images were adjusted at the same level for both cell clusters. The outlines of both cell clusters are delineated by dashed lines. Scale bars: 10 µm. <b>C,</b> Representative calcium response of LNs to 5000 ng bombykol in false colors. <b>D,</b> Representative time courses of LN calcium responses, same sample as in (C). Black bar under time courses indicates stimulus. <b>E,</b> Concentration-response characteristics of LNs in MGC (magenta) and in the OGR (green). Calcium responses were integrated over 3 s following stimulus onset (*: P<0.05, between both regions at given concentration, n = 7, Wilcoxon signed-rank test, means±SEM). D: dorsal, M: medial, MGC: macroglomerular complex, OGR: ordinary glomerular region. The outline of the AL is delineated by dashed lines.</p