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Anatomical Organization of Multiple Modulatory Inputs in a Rhythmic Motor System.

Swallie SE, Monti AM, Blitz DM - PLoS ONE (2015)

Bottom Line: The POC neuron terminals form a defined neuroendocrine organ (anterior commissural organ: ACO) that utilizes peptidergic paracrine signaling to act on MCN1.The MCN1 arborization consistently coincided with the ACO structure, despite morphological variation between preparations.Contrary to a previous 2D study, our 3D analysis revealed that GPR axons did not terminate in a compact bundle, but arborized more extensively near MCN1, arguing against sparse connectivity of GPR onto MCN1.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Miami University, Oxford, OH, United States of America.

ABSTRACT
In rhythmic motor systems, descending projection neuron inputs elicit distinct outputs from their target central pattern generator (CPG) circuits. Projection neuron activity is regulated by sensory inputs and inputs from other regions of the nervous system, relaying information about the current status of an organism. To gain insight into the organization of multiple inputs targeting a projection neuron, we used the identified neuron MCN1 in the stomatogastric nervous system of the crab, Cancer borealis. MCN1 originates in the commissural ganglion and projects to the stomatogastric ganglion (STG). MCN1 activity is differentially regulated by multiple inputs including neuroendocrine (POC) and proprioceptive (GPR) neurons, to elicit distinct outputs from CPG circuits in the STG. We asked whether these defined inputs are compact and spatially segregated or dispersed and overlapping relative to their target projection neuron. Immunocytochemical labeling, intracellular dye injection and three-dimensional (3D) confocal microscopy revealed overlap of MCN1 neurites and POC and GPR terminals. The POC neuron terminals form a defined neuroendocrine organ (anterior commissural organ: ACO) that utilizes peptidergic paracrine signaling to act on MCN1. The MCN1 arborization consistently coincided with the ACO structure, despite morphological variation between preparations. Contrary to a previous 2D study, our 3D analysis revealed that GPR axons did not terminate in a compact bundle, but arborized more extensively near MCN1, arguing against sparse connectivity of GPR onto MCN1. Consistent innervation patterns suggest that integration of the sensory GPR and peptidergic POC inputs occur through more distributed and more tightly constrained anatomical interactions with their common modulatory projection neuron target than anticipated.

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GPR projects dorsally and reaches the level of the ACO.(A) The GPR axons (filled arrowheads) entered the CoG ventrally, projected into the anterior region of the CoG, and then turned to project dorsally where the ACO (arrow) was located (268 slices, 0.8 μm interval). The CoG was imaged from the dorsal surface and the 3D rendering rotated to obtain this side view. (B) In a view from the dorsal surface of the same CoG as in (A) fine branches of the GPR axons (green: open arrowheads) after the axons defasciculated occurred in gaps in the ACO structure (red) (30 slices, 0.8 μm interval).
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pone.0142956.g011: GPR projects dorsally and reaches the level of the ACO.(A) The GPR axons (filled arrowheads) entered the CoG ventrally, projected into the anterior region of the CoG, and then turned to project dorsally where the ACO (arrow) was located (268 slices, 0.8 μm interval). The CoG was imaged from the dorsal surface and the 3D rendering rotated to obtain this side view. (B) In a view from the dorsal surface of the same CoG as in (A) fine branches of the GPR axons (green: open arrowheads) after the axons defasciculated occurred in gaps in the ACO structure (red) (30 slices, 0.8 μm interval).

Mentions: The tissue was scanned using a Zeiss 710 laser scanning confocal microscope using dry objectives (10x, NA = 0.30; 20x, NA = 0.80; 40x, NA = 0.75). Images were obtained on a 1,024 x 1,024 grid field of view. Differential interference contrast (DIC) was used to take single slice images at various depths through the ganglion to view the outline of the tissue. Zen software (ZEN 2009, Zeiss) was used for image processing including contrast enhancements, maximum intensity projections, 3D analysis, volume rendering and depth coding. For some images, small uniform increases in brightness and contrast were applied with Corel Photo-paint (Corel Corporation) to brighten images (Figs 6D–6F, 7, 10 and 11). To optimally visualize 3D relationships within the volume of an image, maximum projections or volume renderings were used. Specifically, maximum intensity projection refers to 2D images in which each pixel contained the maximum intensity in that pixel location when compared across all slices within a z-stack. For volume rendering, 3D images were calculated with a transparent effect and rendered as 2D images using Zen software. Depth coding applied a pseudocolor code based on the z plane of each optical slice within a z-stack (Zen software). Images in figures are single optical slices, maximum projections or volume renderings of an image stack as indicated.


Anatomical Organization of Multiple Modulatory Inputs in a Rhythmic Motor System.

Swallie SE, Monti AM, Blitz DM - PLoS ONE (2015)

GPR projects dorsally and reaches the level of the ACO.(A) The GPR axons (filled arrowheads) entered the CoG ventrally, projected into the anterior region of the CoG, and then turned to project dorsally where the ACO (arrow) was located (268 slices, 0.8 μm interval). The CoG was imaged from the dorsal surface and the 3D rendering rotated to obtain this side view. (B) In a view from the dorsal surface of the same CoG as in (A) fine branches of the GPR axons (green: open arrowheads) after the axons defasciculated occurred in gaps in the ACO structure (red) (30 slices, 0.8 μm interval).
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4643987&req=5

pone.0142956.g011: GPR projects dorsally and reaches the level of the ACO.(A) The GPR axons (filled arrowheads) entered the CoG ventrally, projected into the anterior region of the CoG, and then turned to project dorsally where the ACO (arrow) was located (268 slices, 0.8 μm interval). The CoG was imaged from the dorsal surface and the 3D rendering rotated to obtain this side view. (B) In a view from the dorsal surface of the same CoG as in (A) fine branches of the GPR axons (green: open arrowheads) after the axons defasciculated occurred in gaps in the ACO structure (red) (30 slices, 0.8 μm interval).
Mentions: The tissue was scanned using a Zeiss 710 laser scanning confocal microscope using dry objectives (10x, NA = 0.30; 20x, NA = 0.80; 40x, NA = 0.75). Images were obtained on a 1,024 x 1,024 grid field of view. Differential interference contrast (DIC) was used to take single slice images at various depths through the ganglion to view the outline of the tissue. Zen software (ZEN 2009, Zeiss) was used for image processing including contrast enhancements, maximum intensity projections, 3D analysis, volume rendering and depth coding. For some images, small uniform increases in brightness and contrast were applied with Corel Photo-paint (Corel Corporation) to brighten images (Figs 6D–6F, 7, 10 and 11). To optimally visualize 3D relationships within the volume of an image, maximum projections or volume renderings were used. Specifically, maximum intensity projection refers to 2D images in which each pixel contained the maximum intensity in that pixel location when compared across all slices within a z-stack. For volume rendering, 3D images were calculated with a transparent effect and rendered as 2D images using Zen software. Depth coding applied a pseudocolor code based on the z plane of each optical slice within a z-stack (Zen software). Images in figures are single optical slices, maximum projections or volume renderings of an image stack as indicated.

Bottom Line: The POC neuron terminals form a defined neuroendocrine organ (anterior commissural organ: ACO) that utilizes peptidergic paracrine signaling to act on MCN1.The MCN1 arborization consistently coincided with the ACO structure, despite morphological variation between preparations.Contrary to a previous 2D study, our 3D analysis revealed that GPR axons did not terminate in a compact bundle, but arborized more extensively near MCN1, arguing against sparse connectivity of GPR onto MCN1.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Miami University, Oxford, OH, United States of America.

ABSTRACT
In rhythmic motor systems, descending projection neuron inputs elicit distinct outputs from their target central pattern generator (CPG) circuits. Projection neuron activity is regulated by sensory inputs and inputs from other regions of the nervous system, relaying information about the current status of an organism. To gain insight into the organization of multiple inputs targeting a projection neuron, we used the identified neuron MCN1 in the stomatogastric nervous system of the crab, Cancer borealis. MCN1 originates in the commissural ganglion and projects to the stomatogastric ganglion (STG). MCN1 activity is differentially regulated by multiple inputs including neuroendocrine (POC) and proprioceptive (GPR) neurons, to elicit distinct outputs from CPG circuits in the STG. We asked whether these defined inputs are compact and spatially segregated or dispersed and overlapping relative to their target projection neuron. Immunocytochemical labeling, intracellular dye injection and three-dimensional (3D) confocal microscopy revealed overlap of MCN1 neurites and POC and GPR terminals. The POC neuron terminals form a defined neuroendocrine organ (anterior commissural organ: ACO) that utilizes peptidergic paracrine signaling to act on MCN1. The MCN1 arborization consistently coincided with the ACO structure, despite morphological variation between preparations. Contrary to a previous 2D study, our 3D analysis revealed that GPR axons did not terminate in a compact bundle, but arborized more extensively near MCN1, arguing against sparse connectivity of GPR onto MCN1. Consistent innervation patterns suggest that integration of the sensory GPR and peptidergic POC inputs occur through more distributed and more tightly constrained anatomical interactions with their common modulatory projection neuron target than anticipated.

Show MeSH
Related in: MedlinePlus