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Selective Requirement for Maintenance of Synaptic Contacts onto Motoneurons by Target-Derived trkB Receptors.

Zhu X, Ward PJ, English AW - Neural Plast. (2016)

Bottom Line: Selective knockout of the trkB gene resulted in a marked reduction in contacts made by VGLUT2- and GAD67-immunoreactive structures in both sexes and a significant reduction in contacts containing only glycine in male mice.No reduction was found for glycinergic contacts in female mice or for VGLUT1 immunoreactive contacts in either sex.Signaling through postsynaptic trkB receptors is considered to be an essential part of a cellular mechanism for maintaining the contacts of some, but not all, synaptic contacts onto motoneurons.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322, USA.

ABSTRACT
Synaptic contacts onto motoneurons were studied in mice in which the gene for the trkB neurotrophin receptor was knocked out selectively in a subset of spinal motoneurons. The extent of contacts by structures immunoreactive for either of two different vesicular glutamate transporters (VGLUT1 and VGLUT2), the vesicular GABA transporter, or glutamic acid decarboxylase 67 (GAD67) with the somata of motoneurons, was studied in wild type and trkB knockout cells in tamoxifen treated male and female SLICK-trkB(-/-) mice. Selective knockout of the trkB gene resulted in a marked reduction in contacts made by VGLUT2- and GAD67-immunoreactive structures in both sexes and a significant reduction in contacts containing only glycine in male mice. No reduction was found for glycinergic contacts in female mice or for VGLUT1 immunoreactive contacts in either sex. Signaling through postsynaptic trkB receptors is considered to be an essential part of a cellular mechanism for maintaining the contacts of some, but not all, synaptic contacts onto motoneurons.

No MeSH data available.


Related in: MedlinePlus

(a) Two motoneurons in a single optical section in lamina IX of the ventral horn of the lumbar spinal cord of a tamoxifen treated SLICK::trkBf/f mouse are shown. Both neurons are marked by the presence of a red fluorescent retrograde tracer, cholera toxin B-Alexa Fluor 546, that had been injected into the gastrocnemius muscles three days prior to tissue harvesting, identifying these cells as motoneurons. One of the cells also expresses yellow fluorescent protein (YFP) and was assumed to be  for the gene for trkB. Cyan structures are immunoreactive for glutamic acid decarboxylase 67 (GAD67). (b) Profile plots are shown for GAD67 immunoreactivity along the perimeters of these cells. In each plot, the average fluorescence intensity + one standard deviation is shown as a threshold by the horizontal dashed line. Fluorescence intensity values greater than this threshold are assumed to represent contacts between the perimeter of the cell and structures immunoreactive for GAD67. The numbers next to each plot indicate the percent of the perimeter of the cell in such contact.
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fig2: (a) Two motoneurons in a single optical section in lamina IX of the ventral horn of the lumbar spinal cord of a tamoxifen treated SLICK::trkBf/f mouse are shown. Both neurons are marked by the presence of a red fluorescent retrograde tracer, cholera toxin B-Alexa Fluor 546, that had been injected into the gastrocnemius muscles three days prior to tissue harvesting, identifying these cells as motoneurons. One of the cells also expresses yellow fluorescent protein (YFP) and was assumed to be for the gene for trkB. Cyan structures are immunoreactive for glutamic acid decarboxylase 67 (GAD67). (b) Profile plots are shown for GAD67 immunoreactivity along the perimeters of these cells. In each plot, the average fluorescence intensity + one standard deviation is shown as a threshold by the horizontal dashed line. Fluorescence intensity values greater than this threshold are assumed to represent contacts between the perimeter of the cell and structures immunoreactive for GAD67. The numbers next to each plot indicate the percent of the perimeter of the cell in such contact.

Mentions: From the selected images of presumed motoneurons, the extent of contacts made by different types of synaptic inputs was measured using the computer program FIJI. A region of interest (ROI) was created to select the perimeter of each labeled motoneuron soma and very most proximal dendrites in the red channel of the RGB images, using the thresholding function of the software. The ROIs included only proximal-most dendrites, extending no longer than 25 μm from the center of the cell somata, as the majority of the synapse withdrawal observed immediately following peripheral axotomy occurs in this region [1]. At more prolonged survival times, more subtle changes in VGLUT1+ synaptic contacts occur at more distal sites, as preterminal axon branches withdraw [4]. These changes were not investigated in this study. A plot profile (Figure 2(b), red and green lines), indicating the intensity of immunofluorescence for synapse-associated proteins beneath this outline (±1 micrometer width) of the boundary of the cell studied, was then generated from the blue channel of the RGB image, the component of the RGB image obtained using far red optics. Mean fluorescence intensity along this perimeter was determined and an intensity threshold was set at this mean plus one standard deviation about that mean [2, 36] (horizontal dashed lines in Figure 2(b)). All profile plot values greater than this threshold were assumed to indicate contact of the motoneuron soma by structures immunoreactive for one of the synapse-specific proteins. The proportion of the entire cell perimeter so contacted, that is, the proportion of the cell perimeter with fluorescence intensity values greater than threshold, was found for each cell and expressed as percent synaptic coverage.


Selective Requirement for Maintenance of Synaptic Contacts onto Motoneurons by Target-Derived trkB Receptors.

Zhu X, Ward PJ, English AW - Neural Plast. (2016)

(a) Two motoneurons in a single optical section in lamina IX of the ventral horn of the lumbar spinal cord of a tamoxifen treated SLICK::trkBf/f mouse are shown. Both neurons are marked by the presence of a red fluorescent retrograde tracer, cholera toxin B-Alexa Fluor 546, that had been injected into the gastrocnemius muscles three days prior to tissue harvesting, identifying these cells as motoneurons. One of the cells also expresses yellow fluorescent protein (YFP) and was assumed to be  for the gene for trkB. Cyan structures are immunoreactive for glutamic acid decarboxylase 67 (GAD67). (b) Profile plots are shown for GAD67 immunoreactivity along the perimeters of these cells. In each plot, the average fluorescence intensity + one standard deviation is shown as a threshold by the horizontal dashed line. Fluorescence intensity values greater than this threshold are assumed to represent contacts between the perimeter of the cell and structures immunoreactive for GAD67. The numbers next to each plot indicate the percent of the perimeter of the cell in such contact.
© Copyright Policy - open-access
Related In: Results  -  Collection

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fig2: (a) Two motoneurons in a single optical section in lamina IX of the ventral horn of the lumbar spinal cord of a tamoxifen treated SLICK::trkBf/f mouse are shown. Both neurons are marked by the presence of a red fluorescent retrograde tracer, cholera toxin B-Alexa Fluor 546, that had been injected into the gastrocnemius muscles three days prior to tissue harvesting, identifying these cells as motoneurons. One of the cells also expresses yellow fluorescent protein (YFP) and was assumed to be for the gene for trkB. Cyan structures are immunoreactive for glutamic acid decarboxylase 67 (GAD67). (b) Profile plots are shown for GAD67 immunoreactivity along the perimeters of these cells. In each plot, the average fluorescence intensity + one standard deviation is shown as a threshold by the horizontal dashed line. Fluorescence intensity values greater than this threshold are assumed to represent contacts between the perimeter of the cell and structures immunoreactive for GAD67. The numbers next to each plot indicate the percent of the perimeter of the cell in such contact.
Mentions: From the selected images of presumed motoneurons, the extent of contacts made by different types of synaptic inputs was measured using the computer program FIJI. A region of interest (ROI) was created to select the perimeter of each labeled motoneuron soma and very most proximal dendrites in the red channel of the RGB images, using the thresholding function of the software. The ROIs included only proximal-most dendrites, extending no longer than 25 μm from the center of the cell somata, as the majority of the synapse withdrawal observed immediately following peripheral axotomy occurs in this region [1]. At more prolonged survival times, more subtle changes in VGLUT1+ synaptic contacts occur at more distal sites, as preterminal axon branches withdraw [4]. These changes were not investigated in this study. A plot profile (Figure 2(b), red and green lines), indicating the intensity of immunofluorescence for synapse-associated proteins beneath this outline (±1 micrometer width) of the boundary of the cell studied, was then generated from the blue channel of the RGB image, the component of the RGB image obtained using far red optics. Mean fluorescence intensity along this perimeter was determined and an intensity threshold was set at this mean plus one standard deviation about that mean [2, 36] (horizontal dashed lines in Figure 2(b)). All profile plot values greater than this threshold were assumed to indicate contact of the motoneuron soma by structures immunoreactive for one of the synapse-specific proteins. The proportion of the entire cell perimeter so contacted, that is, the proportion of the cell perimeter with fluorescence intensity values greater than threshold, was found for each cell and expressed as percent synaptic coverage.

Bottom Line: Selective knockout of the trkB gene resulted in a marked reduction in contacts made by VGLUT2- and GAD67-immunoreactive structures in both sexes and a significant reduction in contacts containing only glycine in male mice.No reduction was found for glycinergic contacts in female mice or for VGLUT1 immunoreactive contacts in either sex.Signaling through postsynaptic trkB receptors is considered to be an essential part of a cellular mechanism for maintaining the contacts of some, but not all, synaptic contacts onto motoneurons.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322, USA.

ABSTRACT
Synaptic contacts onto motoneurons were studied in mice in which the gene for the trkB neurotrophin receptor was knocked out selectively in a subset of spinal motoneurons. The extent of contacts by structures immunoreactive for either of two different vesicular glutamate transporters (VGLUT1 and VGLUT2), the vesicular GABA transporter, or glutamic acid decarboxylase 67 (GAD67) with the somata of motoneurons, was studied in wild type and trkB knockout cells in tamoxifen treated male and female SLICK-trkB(-/-) mice. Selective knockout of the trkB gene resulted in a marked reduction in contacts made by VGLUT2- and GAD67-immunoreactive structures in both sexes and a significant reduction in contacts containing only glycine in male mice. No reduction was found for glycinergic contacts in female mice or for VGLUT1 immunoreactive contacts in either sex. Signaling through postsynaptic trkB receptors is considered to be an essential part of a cellular mechanism for maintaining the contacts of some, but not all, synaptic contacts onto motoneurons.

No MeSH data available.


Related in: MedlinePlus