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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

Representative example showing cortical labeling patterns following a retrograde tracer (fluorogold, FG) deposit into the Sp5ic nucleus. (A) Horizontal section through brainstem showing location of the FG injection site. (B) Adjacent horizontal section showing the presence of clusters of retrogradely labeled cells (arrows) located in Sp5ic and Sp5c. White boxes denote insets shown at greater magnification in panels (C–D). (E) Horizontal section through layer IV of the contralateral S1 cortex visualized for CO staining showing the spatial extents of the S1 barrel field, S2 and PPM/PC. (F,F′). Two horizontal sections through infragranular layers, processed for visualization of the tracer, showing retrogradely labeled cells in S1, S2 and PPC/PM. (G) Digital reconstructions of the positions of the retrogradely labeled cells shown superimposed upon outlines of layer IV barrels and inter-barrel septa obtained from the CO-stained section. The sections containing the CO stained barrel field and the retrogradely labeled cells were aligned using blood vessels running orthogonal to the cortical surface (panels (E,F,F′) arrows) as control points.
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Figure 6: Representative example showing cortical labeling patterns following a retrograde tracer (fluorogold, FG) deposit into the Sp5ic nucleus. (A) Horizontal section through brainstem showing location of the FG injection site. (B) Adjacent horizontal section showing the presence of clusters of retrogradely labeled cells (arrows) located in Sp5ic and Sp5c. White boxes denote insets shown at greater magnification in panels (C–D). (E) Horizontal section through layer IV of the contralateral S1 cortex visualized for CO staining showing the spatial extents of the S1 barrel field, S2 and PPM/PC. (F,F′). Two horizontal sections through infragranular layers, processed for visualization of the tracer, showing retrogradely labeled cells in S1, S2 and PPC/PM. (G) Digital reconstructions of the positions of the retrogradely labeled cells shown superimposed upon outlines of layer IV barrels and inter-barrel septa obtained from the CO-stained section. The sections containing the CO stained barrel field and the retrogradely labeled cells were aligned using blood vessels running orthogonal to the cortical surface (panels (E,F,F′) arrows) as control points.

Mentions: To complement our anterograde tracing data, we injected FG into various trigeminal nuclei at different rostro-caudal levels in eight rats. Figure 6 shows a representative example where the FG deposit was placed in the Sp5ic nucleus (Figure 6A). As reported before Furuta et al. (2010), one of the largest sources of projections to the trigeminal nuclei are other trigeminal nuclei and we observed a dense strip of retrogradely labeled cells stretching caudally from the injection site (Figure 6B). Retrogradely cells were found within the Sp5ic itself (Figure 6C) and in the Sp5c (Figure 6D). In cortex, retrogradely labeled cells were distributed across the S1 barrel cortex (Figures 6F,F′) spanning both barrel and septal columns (Figure 6G) as well as S2 and the PPC/PM (Figures 6F,F′). Barrel and septal columns were defined as regions in supra- and infragranular layers vertically aligned with layer IV barrels and septa respectively (Alloway et al., 2004; Chakrabarti and Alloway, 2006). Retrogradely labeled cells were located exclusively in the infragranular layers (layers V/VI). It is noteworthy to mention that there was a complete absence of retrogradely labeled cells within the M1 vibrissal representation as defined by stereotaxic coordinates. This is in accordance with previous reports (Miyashita et al., 1994; Urbain and Deschênes, 2007).


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)

Representative example showing cortical labeling patterns following a retrograde tracer (fluorogold, FG) deposit into the Sp5ic nucleus. (A) Horizontal section through brainstem showing location of the FG injection site. (B) Adjacent horizontal section showing the presence of clusters of retrogradely labeled cells (arrows) located in Sp5ic and Sp5c. White boxes denote insets shown at greater magnification in panels (C–D). (E) Horizontal section through layer IV of the contralateral S1 cortex visualized for CO staining showing the spatial extents of the S1 barrel field, S2 and PPM/PC. (F,F′). Two horizontal sections through infragranular layers, processed for visualization of the tracer, showing retrogradely labeled cells in S1, S2 and PPC/PM. (G) Digital reconstructions of the positions of the retrogradely labeled cells shown superimposed upon outlines of layer IV barrels and inter-barrel septa obtained from the CO-stained section. The sections containing the CO stained barrel field and the retrogradely labeled cells were aligned using blood vessels running orthogonal to the cortical surface (panels (E,F,F′) arrows) as control points.
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Related In: Results  -  Collection

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Figure 6: Representative example showing cortical labeling patterns following a retrograde tracer (fluorogold, FG) deposit into the Sp5ic nucleus. (A) Horizontal section through brainstem showing location of the FG injection site. (B) Adjacent horizontal section showing the presence of clusters of retrogradely labeled cells (arrows) located in Sp5ic and Sp5c. White boxes denote insets shown at greater magnification in panels (C–D). (E) Horizontal section through layer IV of the contralateral S1 cortex visualized for CO staining showing the spatial extents of the S1 barrel field, S2 and PPM/PC. (F,F′). Two horizontal sections through infragranular layers, processed for visualization of the tracer, showing retrogradely labeled cells in S1, S2 and PPC/PM. (G) Digital reconstructions of the positions of the retrogradely labeled cells shown superimposed upon outlines of layer IV barrels and inter-barrel septa obtained from the CO-stained section. The sections containing the CO stained barrel field and the retrogradely labeled cells were aligned using blood vessels running orthogonal to the cortical surface (panels (E,F,F′) arrows) as control points.
Mentions: To complement our anterograde tracing data, we injected FG into various trigeminal nuclei at different rostro-caudal levels in eight rats. Figure 6 shows a representative example where the FG deposit was placed in the Sp5ic nucleus (Figure 6A). As reported before Furuta et al. (2010), one of the largest sources of projections to the trigeminal nuclei are other trigeminal nuclei and we observed a dense strip of retrogradely labeled cells stretching caudally from the injection site (Figure 6B). Retrogradely cells were found within the Sp5ic itself (Figure 6C) and in the Sp5c (Figure 6D). In cortex, retrogradely labeled cells were distributed across the S1 barrel cortex (Figures 6F,F′) spanning both barrel and septal columns (Figure 6G) as well as S2 and the PPC/PM (Figures 6F,F′). Barrel and septal columns were defined as regions in supra- and infragranular layers vertically aligned with layer IV barrels and septa respectively (Alloway et al., 2004; Chakrabarti and Alloway, 2006). Retrogradely labeled cells were located exclusively in the infragranular layers (layers V/VI). It is noteworthy to mention that there was a complete absence of retrogradely labeled cells within the M1 vibrissal representation as defined by stereotaxic coordinates. This is in accordance with previous reports (Miyashita et al., 1994; Urbain and Deschênes, 2007).

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