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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

A representative example showing the laminar distribution of retrogradely labeled cells in cortex following a tracer deposit into the Sp5ic. (A) Horizontal section through the brainstem showing the location of the injection site in Sp5ic. (B) Coronal section through cortex showing the layer IV barrels (asterisks) in relation to the retrogradely labeled cells. The layer boundaries have been drawn from neighboring sections stained for CO and superimposed on this section. (C) Inset from (B), shown at higher magnification, showing the retrogradely labeled cells with the presence of apical dendrites (arrowhead).
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Figure 8: A representative example showing the laminar distribution of retrogradely labeled cells in cortex following a tracer deposit into the Sp5ic. (A) Horizontal section through the brainstem showing the location of the injection site in Sp5ic. (B) Coronal section through cortex showing the layer IV barrels (asterisks) in relation to the retrogradely labeled cells. The layer boundaries have been drawn from neighboring sections stained for CO and superimposed on this section. (C) Inset from (B), shown at higher magnification, showing the retrogradely labeled cells with the presence of apical dendrites (arrowhead).

Mentions: To determine the laminar origin of these corticofugal projections, two rats were injected with FG in the Sp5ic. In these cases, S1 and S2 were sectioned coronally instead of tangentially (Figure 8). As illustrated in Figure 8B, the retrogradely labeled cells reside in infragranular layer Vb. When comparing the position of the retrogradely labeled cells with the CO barrels, seen as lightly stained “ghost” structures in layer IV, it can be seen once again that the retrogradely labeled cells fall within both barrel and septal columns. The retrogradely labeled cells appeared to be large pyramidal neurons (Figure 8C) with an apical dendrite coursing towards the superficial layers (arrowhead).


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)

A representative example showing the laminar distribution of retrogradely labeled cells in cortex following a tracer deposit into the Sp5ic. (A) Horizontal section through the brainstem showing the location of the injection site in Sp5ic. (B) Coronal section through cortex showing the layer IV barrels (asterisks) in relation to the retrogradely labeled cells. The layer boundaries have been drawn from neighboring sections stained for CO and superimposed on this section. (C) Inset from (B), shown at higher magnification, showing the retrogradely labeled cells with the presence of apical dendrites (arrowhead).
© Copyright Policy
Related In: Results  -  Collection

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

Figure 8: A representative example showing the laminar distribution of retrogradely labeled cells in cortex following a tracer deposit into the Sp5ic. (A) Horizontal section through the brainstem showing the location of the injection site in Sp5ic. (B) Coronal section through cortex showing the layer IV barrels (asterisks) in relation to the retrogradely labeled cells. The layer boundaries have been drawn from neighboring sections stained for CO and superimposed on this section. (C) Inset from (B), shown at higher magnification, showing the retrogradely labeled cells with the presence of apical dendrites (arrowhead).
Mentions: To determine the laminar origin of these corticofugal projections, two rats were injected with FG in the Sp5ic. In these cases, S1 and S2 were sectioned coronally instead of tangentially (Figure 8). As illustrated in Figure 8B, the retrogradely labeled cells reside in infragranular layer Vb. When comparing the position of the retrogradely labeled cells with the CO barrels, seen as lightly stained “ghost” structures in layer IV, it can be seen once again that the retrogradely labeled cells fall within both barrel and septal columns. The retrogradely labeled cells appeared to be large pyramidal neurons (Figure 8C) with an apical dendrite coursing towards the superficial layers (arrowhead).

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