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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

Digital reconstructions of anterogradely-labeled terminals in five horizontal sections spanning the entire dorsoventral extent of the trigeminal sensory nuclei. Labeled S1 corticofugal terminals are shown in blue, S2 terminals in red. Sections are arranged from the most dorsal (A) to the most ventral (E). Outlines of the different trigeminal sensory nuclei, defined using adjacent CO sections are shown superimposed on the plotted terminals. Consecutive sections were 180 μm apart.
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Figure 2: Digital reconstructions of anterogradely-labeled terminals in five horizontal sections spanning the entire dorsoventral extent of the trigeminal sensory nuclei. Labeled S1 corticofugal terminals are shown in blue, S2 terminals in red. Sections are arranged from the most dorsal (A) to the most ventral (E). Outlines of the different trigeminal sensory nuclei, defined using adjacent CO sections are shown superimposed on the plotted terminals. Consecutive sections were 180 μm apart.

Mentions: These differences between S1 and S2 corticofugal labeling patterns were best visualized when examining trigeminal brainstem horizontal sections at different dorso-ventral levels. As seen in Figures 2A,B, at more dorsal levels, the labeled terminals from both S1 and S2 were distributed in discrete patches centered in Pr5, Sp5ic and Sp5c. These patches of labeling were mostly separated by zones of little or no labeling in between them. The S1 terminals were distributed in three separate clusters located in the Pr5, Sp5ic and Sp5c nuclei whereas the S2 terminals also innervated the Sp5o nucleus. In ventral sections, S1 labeling in Sp5c became scant with dense labeling in Pr5 and Sp5ic, and some labeled terminals in Sp5ir (Figure 2C), whereas the labeled projection terminals from S2 were more evenly distributed across all of the different trigeminal sensory nuclei (Figures 2C–E). Thus, Pr5, Sp5ic, Sp5c, received both S1 and S2 projections whereas Sp5o and Sp5ir received mainly S2 projections. Labeling in Pr5 frequently exhibited a discrete, mirrored pattern with S1 terminating in a lateral patch and S2 terminating in a medial patch. Corticofugal projections to Sp5c had a distinct dorso-ventral gradient with most S1 projections targeting dorsal Sp5c whereas S2 projections spanned the entire dorso-ventral extent of the nucleus.


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)

Digital reconstructions of anterogradely-labeled terminals in five horizontal sections spanning the entire dorsoventral extent of the trigeminal sensory nuclei. Labeled S1 corticofugal terminals are shown in blue, S2 terminals in red. Sections are arranged from the most dorsal (A) to the most ventral (E). Outlines of the different trigeminal sensory nuclei, defined using adjacent CO sections are shown superimposed on the plotted terminals. Consecutive sections were 180 μm apart.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 2: Digital reconstructions of anterogradely-labeled terminals in five horizontal sections spanning the entire dorsoventral extent of the trigeminal sensory nuclei. Labeled S1 corticofugal terminals are shown in blue, S2 terminals in red. Sections are arranged from the most dorsal (A) to the most ventral (E). Outlines of the different trigeminal sensory nuclei, defined using adjacent CO sections are shown superimposed on the plotted terminals. Consecutive sections were 180 μm apart.
Mentions: These differences between S1 and S2 corticofugal labeling patterns were best visualized when examining trigeminal brainstem horizontal sections at different dorso-ventral levels. As seen in Figures 2A,B, at more dorsal levels, the labeled terminals from both S1 and S2 were distributed in discrete patches centered in Pr5, Sp5ic and Sp5c. These patches of labeling were mostly separated by zones of little or no labeling in between them. The S1 terminals were distributed in three separate clusters located in the Pr5, Sp5ic and Sp5c nuclei whereas the S2 terminals also innervated the Sp5o nucleus. In ventral sections, S1 labeling in Sp5c became scant with dense labeling in Pr5 and Sp5ic, and some labeled terminals in Sp5ir (Figure 2C), whereas the labeled projection terminals from S2 were more evenly distributed across all of the different trigeminal sensory nuclei (Figures 2C–E). Thus, Pr5, Sp5ic, Sp5c, received both S1 and S2 projections whereas Sp5o and Sp5ir received mainly S2 projections. Labeling in Pr5 frequently exhibited a discrete, mirrored pattern with S1 terminating in a lateral patch and S2 terminating in a medial patch. Corticofugal projections to Sp5c had a distinct dorso-ventral gradient with most S1 projections targeting dorsal Sp5c whereas S2 projections spanned the entire dorso-ventral extent of the nucleus.

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