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Experience-Dependent, Layer-Specific Development of Divergent Thalamocortical Connectivity.

Crocker-Buque A, Brown SM, Kind PC, Isaac JT, Daw MI - Cereb. Cortex (2014)

Bottom Line: Here, we show that, in neonates, the input to layer 6 is as strong as that to layer 4.This strengthening consists of an increase in axon branching and the divergence of connectivity in layer 4 without a change in the strength of individual connections.We propose that experience-driven LTP stabilizes transient TC synapses in layer 4 to increase strength and divergence specifically in layer 4 over layer 6.

View Article: PubMed Central - PubMed

Affiliation: Centre for Integrative Physiology, University of Edinburgh, Edinburgh, UK.

No MeSH data available.


TC axon branching is reduced in deprived cortex. (A) Example images showing DiI labeling (red) of TC axons in cortex with overlaid Topro labeling (right image, blue) to identify cortical layers. (B) Example traced axons in L4 from the spared hemisphere. Middle tracing taken from image shown in A. (C) Example axon traces from L4 in the deprived hemisphere. (D) Example axon traces from L6 in the spared hemisphere. (E) Example axon traces from L6 in the deprived hemisphere. (F) Bar graph showing mean total TC axon length in L4 and L6 in both deprived and spared hemispheres. (G) Bar graph showing the mean lateral spread of TC axons in both deprived and spared hemispheres. (H) Bar graph showing the mean number of TC axon branches in L4 in deprived and spared hemispheres. * P < 0.05, **P < 0.005.
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BHU031F7: TC axon branching is reduced in deprived cortex. (A) Example images showing DiI labeling (red) of TC axons in cortex with overlaid Topro labeling (right image, blue) to identify cortical layers. (B) Example traced axons in L4 from the spared hemisphere. Middle tracing taken from image shown in A. (C) Example axon traces from L4 in the deprived hemisphere. (D) Example axon traces from L6 in the spared hemisphere. (E) Example axon traces from L6 in the deprived hemisphere. (F) Bar graph showing mean total TC axon length in L4 and L6 in both deprived and spared hemispheres. (G) Bar graph showing the mean lateral spread of TC axons in both deprived and spared hemispheres. (H) Bar graph showing the mean number of TC axon branches in L4 in deprived and spared hemispheres. * P < 0.05, **P < 0.005.

Mentions: Small crystals of 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate (DiI; Life Technologies, Carlsbad, CA, USA) were placed into the ventral posteromedial nucleus of the thalamus and left free floating in PBS for 14 days. L4 and barrel boundaries were identified by examining morphology and density of cells counterstained with TOPRO3 (1 : 1000; T3605; Invitrogen, Fig. 7A) Sections were imaged on an LSM510 Axiovert confocal microscope (Carl Zeiss). Three-micrometer confocal stacks were taken through L4 of the primary somatosensory cortex. DiI-labeled axons that left the section in the z-plane were not analyzed. The period of DiI transport required to fully label axons in L4 resulted in dense labeling in L6 such that individual axons were difficult to trace. We therefore analyzed individual TC axon branches entering L4 rather than entire TC axon arbors. This also required that axons in L6 were imaged in a separate set of experiments with shorter transport time. Sections containing back-labeled cells were discarded and only axons originating in the white matter were traced. As the L5/L6 border was not always readily identifiable in these sections, axons were traced from the white matter to 50% of the distance between the white matter and the more easily identified L4/L5 border. A maximum of 4 axons (mean 2.4 ± 0.2 axons) from each hemisphere were traced to provide a mean measurement for a single hemisphere. Inferential statistics were used to compare means derived from individual hemispheres; the number of replicates for each condition (n) was the number of hemispheres not the number of axons traced. Axons were reconstructed and measured using Simple Neurite Tracer plugin (Longair et al. 2011) in ImageJ (US National Institute of Health, Bethesda, MD, USA). Microscopy was done in the IMPACT Imaging Facility at the University of Edinburgh. The experimenter was blind to which hemisphere had been deprived until after analysis.


Experience-Dependent, Layer-Specific Development of Divergent Thalamocortical Connectivity.

Crocker-Buque A, Brown SM, Kind PC, Isaac JT, Daw MI - Cereb. Cortex (2014)

TC axon branching is reduced in deprived cortex. (A) Example images showing DiI labeling (red) of TC axons in cortex with overlaid Topro labeling (right image, blue) to identify cortical layers. (B) Example traced axons in L4 from the spared hemisphere. Middle tracing taken from image shown in A. (C) Example axon traces from L4 in the deprived hemisphere. (D) Example axon traces from L6 in the spared hemisphere. (E) Example axon traces from L6 in the deprived hemisphere. (F) Bar graph showing mean total TC axon length in L4 and L6 in both deprived and spared hemispheres. (G) Bar graph showing the mean lateral spread of TC axons in both deprived and spared hemispheres. (H) Bar graph showing the mean number of TC axon branches in L4 in deprived and spared hemispheres. * P < 0.05, **P < 0.005.
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BHU031F7: TC axon branching is reduced in deprived cortex. (A) Example images showing DiI labeling (red) of TC axons in cortex with overlaid Topro labeling (right image, blue) to identify cortical layers. (B) Example traced axons in L4 from the spared hemisphere. Middle tracing taken from image shown in A. (C) Example axon traces from L4 in the deprived hemisphere. (D) Example axon traces from L6 in the spared hemisphere. (E) Example axon traces from L6 in the deprived hemisphere. (F) Bar graph showing mean total TC axon length in L4 and L6 in both deprived and spared hemispheres. (G) Bar graph showing the mean lateral spread of TC axons in both deprived and spared hemispheres. (H) Bar graph showing the mean number of TC axon branches in L4 in deprived and spared hemispheres. * P < 0.05, **P < 0.005.
Mentions: Small crystals of 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate (DiI; Life Technologies, Carlsbad, CA, USA) were placed into the ventral posteromedial nucleus of the thalamus and left free floating in PBS for 14 days. L4 and barrel boundaries were identified by examining morphology and density of cells counterstained with TOPRO3 (1 : 1000; T3605; Invitrogen, Fig. 7A) Sections were imaged on an LSM510 Axiovert confocal microscope (Carl Zeiss). Three-micrometer confocal stacks were taken through L4 of the primary somatosensory cortex. DiI-labeled axons that left the section in the z-plane were not analyzed. The period of DiI transport required to fully label axons in L4 resulted in dense labeling in L6 such that individual axons were difficult to trace. We therefore analyzed individual TC axon branches entering L4 rather than entire TC axon arbors. This also required that axons in L6 were imaged in a separate set of experiments with shorter transport time. Sections containing back-labeled cells were discarded and only axons originating in the white matter were traced. As the L5/L6 border was not always readily identifiable in these sections, axons were traced from the white matter to 50% of the distance between the white matter and the more easily identified L4/L5 border. A maximum of 4 axons (mean 2.4 ± 0.2 axons) from each hemisphere were traced to provide a mean measurement for a single hemisphere. Inferential statistics were used to compare means derived from individual hemispheres; the number of replicates for each condition (n) was the number of hemispheres not the number of axons traced. Axons were reconstructed and measured using Simple Neurite Tracer plugin (Longair et al. 2011) in ImageJ (US National Institute of Health, Bethesda, MD, USA). Microscopy was done in the IMPACT Imaging Facility at the University of Edinburgh. The experimenter was blind to which hemisphere had been deprived until after analysis.

Bottom Line: Here, we show that, in neonates, the input to layer 6 is as strong as that to layer 4.This strengthening consists of an increase in axon branching and the divergence of connectivity in layer 4 without a change in the strength of individual connections.We propose that experience-driven LTP stabilizes transient TC synapses in layer 4 to increase strength and divergence specifically in layer 4 over layer 6.

View Article: PubMed Central - PubMed

Affiliation: Centre for Integrative Physiology, University of Edinburgh, Edinburgh, UK.

No MeSH data available.