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Corticofugal projection patterns of whisker sensorimotor cortex to the sensory trigeminal nuclei.

Smith JB, Watson GD, Alloway KD, Schwarz C, Chakrabarti S - Front Neural Circuits (2015)

Bottom Line: We confirmed our anterograde tracing results by injecting retrograde tracers at various rostro-caudal levels within the trigeminal sensory nuclei to determine the position of retrogradely labeled cortical cells with respect to S1 barrel cortex.Our results demonstrate that S1 and S2 projections terminate in largely overlapping regions but show some significant differences.Contrary to the view that sensory gating could be mediated by differential activation of inhibitory interconnections between the spinal trigeminal subnuclei, we observed that projections from S1 and S2 are largely overlapping in these subnuclei despite the differences noted earlier.

View Article: PubMed Central - PubMed

Affiliation: Department of Engineering Science and Mechanics, Pennsylvania State University University Park, PA, USA ; Center for Neural Engineering, Huck Institute of Life Sciences, Pennsylvania State University University Park, PA, USA.

ABSTRACT
The primary (S1) and secondary (S2) somatosensory cortices project to several trigeminal sensory nuclei. One putative function of these corticofugal projections is the gating of sensory transmission through the trigeminal principal nucleus (Pr5), and some have proposed that S1 and S2 project differentially to the spinal trigeminal subnuclei, which have inhibitory circuits that could inhibit or disinhibit the output projections of Pr5. Very little, however, is known about the origin of sensorimotor corticofugal projections and their patterns of termination in the various trigeminal nuclei. We addressed this issue by injecting anterograde tracers in S1, S2 and primary motor (M1) cortices, and quantitatively characterizing the distribution of labeled terminals within the entire rostro-caudal chain of trigeminal sub-nuclei. We confirmed our anterograde tracing results by injecting retrograde tracers at various rostro-caudal levels within the trigeminal sensory nuclei to determine the position of retrogradely labeled cortical cells with respect to S1 barrel cortex. Our results demonstrate that S1 and S2 projections terminate in largely overlapping regions but show some significant differences. Whereas S1 projection terminals tend to cluster within the principal trigeminal (Pr5), caudal spinal trigeminal interpolaris (Sp5ic), and the dorsal spinal trigeminal caudalis (Sp5c), S2 projection terminals are distributed in a continuum across all trigeminal nuclei. Contrary to the view that sensory gating could be mediated by differential activation of inhibitory interconnections between the spinal trigeminal subnuclei, we observed that projections from S1 and S2 are largely overlapping in these subnuclei despite the differences noted earlier.

No MeSH data available.


Related in: MedlinePlus

Pattern of corticofugal terminal distribution across trigeminal sensory nuclei in both dorsoventral and rostro-caudal dimensions. (A) Terminal counts from an anterograde tracer injection into S1 cortex, normalized by total S1 terminal counts tallied across all horizontal sections through the brainstem. The different horizontal sections are arranged along the y axis with the dorsal most section located at the top. The rostral and caudal boundaries of the different trigeminal sensory nuclei have been overlaid on top using dotted white lines. All rostrocaudal measurements were normalized to the rostral boundary of the Pr5 nucleus for each section. Three animals are represented in the three rows. The yellow dotted lines in the second row denote the section shown in Figure 1D. (B) Identical plots for terminals labeled with an anterograde tracer injected into S2. All rostrocaudal distances are in mm.
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Figure 4: Pattern of corticofugal terminal distribution across trigeminal sensory nuclei in both dorsoventral and rostro-caudal dimensions. (A) Terminal counts from an anterograde tracer injection into S1 cortex, normalized by total S1 terminal counts tallied across all horizontal sections through the brainstem. The different horizontal sections are arranged along the y axis with the dorsal most section located at the top. The rostral and caudal boundaries of the different trigeminal sensory nuclei have been overlaid on top using dotted white lines. All rostrocaudal measurements were normalized to the rostral boundary of the Pr5 nucleus for each section. Three animals are represented in the three rows. The yellow dotted lines in the second row denote the section shown in Figure 1D. (B) Identical plots for terminals labeled with an anterograde tracer injected into S2. All rostrocaudal distances are in mm.

Mentions: All plotted reconstructions, which contain plots of varicosities, retrogradely-labeled cells, and section outlines were transferred to the MATLAB (Mathworks, Natick, MA, USA, Ver. 2013b) environment where further analyses were performed. To quantify anterograde labeling in brainstem trigeminal sensory nuclei, each plotted section was loaded and aligned with the sections from other dorsoventral levels using a simple affine image transformation (Image Processing Toolbox). To quantify labeling in different nuclei, all labeled terminals within the respective nuclear boundaries were counted. To obtain three dimensional distributions (Figure 4), labeled terminals were counted in 200 μm rostro-caudal bins for each section (dorsoventral level, section thickness: 60 μm), aligned to the rostral border of Pr5 for each section, and displayed using a 3D surface plot. Dorsal sections where nuclear boundaries could not be discerned from the CO sections were not included (black rows). To obtain rostro-caudal distributions of labeled terminals (Figure 5), each trigeminal sensory nucleus was binned using 10 equal bins and the varicosity count calculated. All terminal counts were normalized by the total number of terminals resulting from that particular injection to account for differences in tracer volumes injected into different cortical areas.


Corticofugal projection patterns of whisker sensorimotor cortex to the sensory trigeminal nuclei.

Smith JB, Watson GD, Alloway KD, Schwarz C, Chakrabarti S - Front Neural Circuits (2015)

Pattern of corticofugal terminal distribution across trigeminal sensory nuclei in both dorsoventral and rostro-caudal dimensions. (A) Terminal counts from an anterograde tracer injection into S1 cortex, normalized by total S1 terminal counts tallied across all horizontal sections through the brainstem. The different horizontal sections are arranged along the y axis with the dorsal most section located at the top. The rostral and caudal boundaries of the different trigeminal sensory nuclei have been overlaid on top using dotted white lines. All rostrocaudal measurements were normalized to the rostral boundary of the Pr5 nucleus for each section. Three animals are represented in the three rows. The yellow dotted lines in the second row denote the section shown in Figure 1D. (B) Identical plots for terminals labeled with an anterograde tracer injected into S2. All rostrocaudal distances are in mm.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4588702&req=5

Figure 4: Pattern of corticofugal terminal distribution across trigeminal sensory nuclei in both dorsoventral and rostro-caudal dimensions. (A) Terminal counts from an anterograde tracer injection into S1 cortex, normalized by total S1 terminal counts tallied across all horizontal sections through the brainstem. The different horizontal sections are arranged along the y axis with the dorsal most section located at the top. The rostral and caudal boundaries of the different trigeminal sensory nuclei have been overlaid on top using dotted white lines. All rostrocaudal measurements were normalized to the rostral boundary of the Pr5 nucleus for each section. Three animals are represented in the three rows. The yellow dotted lines in the second row denote the section shown in Figure 1D. (B) Identical plots for terminals labeled with an anterograde tracer injected into S2. All rostrocaudal distances are in mm.
Mentions: All plotted reconstructions, which contain plots of varicosities, retrogradely-labeled cells, and section outlines were transferred to the MATLAB (Mathworks, Natick, MA, USA, Ver. 2013b) environment where further analyses were performed. To quantify anterograde labeling in brainstem trigeminal sensory nuclei, each plotted section was loaded and aligned with the sections from other dorsoventral levels using a simple affine image transformation (Image Processing Toolbox). To quantify labeling in different nuclei, all labeled terminals within the respective nuclear boundaries were counted. To obtain three dimensional distributions (Figure 4), labeled terminals were counted in 200 μm rostro-caudal bins for each section (dorsoventral level, section thickness: 60 μm), aligned to the rostral border of Pr5 for each section, and displayed using a 3D surface plot. Dorsal sections where nuclear boundaries could not be discerned from the CO sections were not included (black rows). To obtain rostro-caudal distributions of labeled terminals (Figure 5), each trigeminal sensory nucleus was binned using 10 equal bins and the varicosity count calculated. All terminal counts were normalized by the total number of terminals resulting from that particular injection to account for differences in tracer volumes injected into different cortical areas.

Bottom Line: We confirmed our anterograde tracing results by injecting retrograde tracers at various rostro-caudal levels within the trigeminal sensory nuclei to determine the position of retrogradely labeled cortical cells with respect to S1 barrel cortex.Our results demonstrate that S1 and S2 projections terminate in largely overlapping regions but show some significant differences.Contrary to the view that sensory gating could be mediated by differential activation of inhibitory interconnections between the spinal trigeminal subnuclei, we observed that projections from S1 and S2 are largely overlapping in these subnuclei despite the differences noted earlier.

View Article: PubMed Central - PubMed

Affiliation: Department of Engineering Science and Mechanics, Pennsylvania State University University Park, PA, USA ; Center for Neural Engineering, Huck Institute of Life Sciences, Pennsylvania State University University Park, PA, USA.

ABSTRACT
The primary (S1) and secondary (S2) somatosensory cortices project to several trigeminal sensory nuclei. One putative function of these corticofugal projections is the gating of sensory transmission through the trigeminal principal nucleus (Pr5), and some have proposed that S1 and S2 project differentially to the spinal trigeminal subnuclei, which have inhibitory circuits that could inhibit or disinhibit the output projections of Pr5. Very little, however, is known about the origin of sensorimotor corticofugal projections and their patterns of termination in the various trigeminal nuclei. We addressed this issue by injecting anterograde tracers in S1, S2 and primary motor (M1) cortices, and quantitatively characterizing the distribution of labeled terminals within the entire rostro-caudal chain of trigeminal sub-nuclei. We confirmed our anterograde tracing results by injecting retrograde tracers at various rostro-caudal levels within the trigeminal sensory nuclei to determine the position of retrogradely labeled cortical cells with respect to S1 barrel cortex. Our results demonstrate that S1 and S2 projections terminate in largely overlapping regions but show some significant differences. Whereas S1 projection terminals tend to cluster within the principal trigeminal (Pr5), caudal spinal trigeminal interpolaris (Sp5ic), and the dorsal spinal trigeminal caudalis (Sp5c), S2 projection terminals are distributed in a continuum across all trigeminal nuclei. Contrary to the view that sensory gating could be mediated by differential activation of inhibitory interconnections between the spinal trigeminal subnuclei, we observed that projections from S1 and S2 are largely overlapping in these subnuclei despite the differences noted earlier.

No MeSH data available.


Related in: MedlinePlus