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A quantitative study of spinothalamic neurons in laminae I, III, and IV in lumbar and cervical segments of the rat spinal cord.

Al-Khater KM, Kerr R, Todd AJ - J. Comp. Neurol. (2008)

Bottom Line: Our results suggest that there are 90 lamina I spinothalamic neurons per side in C7 and 15 in L4 and that some of those in C7 only project to PoT.We found that 85% of the lamina III/IV NK1r-immunoreactive neurons in C6 and 17% of those in L5 belong to the spinothalamic tract, and these apparently project exclusively to the caudal thalamus, including PoT.Because PoT projects to second somatosensory and insular cortices, our results suggest that these are major targets for information conveyed by both these populations of spinothalamic neurons.

View Article: PubMed Central - PubMed

Affiliation: Spinal Cord Group, Institute of Biomedical & Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom. a.todd@bio.gla.ac.uk

ABSTRACT
The major ascending outputs from superficial spinal dorsal horn consist of projection neurons in lamina I, together with neurons in laminae III-IV that express the neurokinin 1 receptor (NK1r) and have dendrites that enter the superficial laminae. Some neurons in each of these populations belong to the spinothalamic tract, which conveys nociceptive information via the thalamus to cortical areas involved in pain. A projection from the cervical superficial dorsal horn to the posterior triangular nucleus (PoT) has recently been identified. PoT is at the caudal end of the thalamus and was not included in injection sites in many previous retrograde tracing studies. We have injected various tracers (cholera toxin B subunit, Fluoro-Gold, and fluorescent latex microspheres) into the thalamus to estimate the number of spinothalamic neurons in each of these two populations, and to investigate their projection targets. Most lamina I and lamina III/IV NK1r-immunoreactive spinothalamic neurons in cervical and lumbar segments could be labeled from injections centered on PoT. Our results suggest that there are 90 lamina I spinothalamic neurons per side in C7 and 15 in L4 and that some of those in C7 only project to PoT. We found that 85% of the lamina III/IV NK1r-immunoreactive neurons in C6 and 17% of those in L5 belong to the spinothalamic tract, and these apparently project exclusively to the caudal thalamus, including PoT. Because PoT projects to second somatosensory and insular cortices, our results suggest that these are major targets for information conveyed by both these populations of spinothalamic neurons.

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Retrograde labeling of lamina I neurons with fluorescent latex microspheres in parasagittal sections. The top row of images shows an example of a labeled lamina I neuron from C6 in experiment FLM3, and the bottom row shows a labeled neuron in L5 from experiment FLM2. In each case, separate images show the fluorescent latex microspheres (beads, red), NK1r (green) and NeuN (blue), with a merged image on the right. Note the presence of numerous beads in each neuron and that both neurons are NK1r-immunoreactive (arrow). Images are projections of seven (top row) or five (bottom row) confocal optical sections at 1-μm z-spacing. Scale bar = 20 μm in bottom right panel (applies to all).
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fig11: Retrograde labeling of lamina I neurons with fluorescent latex microspheres in parasagittal sections. The top row of images shows an example of a labeled lamina I neuron from C6 in experiment FLM3, and the bottom row shows a labeled neuron in L5 from experiment FLM2. In each case, separate images show the fluorescent latex microspheres (beads, red), NK1r (green) and NeuN (blue), with a merged image on the right. Note the presence of numerous beads in each neuron and that both neurons are NK1r-immunoreactive (arrow). Images are projections of seven (top row) or five (bottom row) confocal optical sections at 1-μm z-spacing. Scale bar = 20 μm in bottom right panel (applies to all).

Mentions: Examples of retrogradely labeled neurons are shown in Figures 11 and 12, and quantitative data are provided in Table 8. The numbers of microspheres in labeled neurons varied considerably: only cells that contained 5 or more were considered to be retrogradely labeled, and most such cells contained more than 10 microspheres. The optical properties of Gel-Mount were not as good as those of Vectashield, and although fluorescent latex microspherescould be identified through the depth of the section, it was difficult to follow NK1r-immunoreactive profiles deep within the sections. In the C6 segment, lamina I was found to contain between 15 and 46 retrogradely labeled cells, whereas 5–10 retrogradely labeled lamina III/IV NK1r-immunoreactive cells were observed, of which 1–6 had dendrites that could be followed into the superficial dorsal horn (Fig. 12a). Because of the difficulty in following NK1r-immunoreactive dendrites in these sections, only those cells that had dorsal dendrites that entered lamina II in the superficial part of the same section could be unequivocally identified as belonging to this type. In the L5 segment, no retrogradely labeled cells were detected in laminae I or III/IV in experiment FLM1, whereas in experiments FLM 2 and FLM3, 4 and 5 lamina I cells (respectively) and 4 and 6 lamina III/IV NK1r cells (respectively) were seen. Dorsal dendrites of two of the lamina III/IV NK1r-immunoreactive cells in experiment FLM3 could be followed into the superficial dorsal horn, and one of these is illustrated in Figure 12b. Although many of the retrogradely labeled lamina I cells in C6 and L5 could be identified as NK1r-immunoreactive (Fig. 11), when the cell was in the deepest part of the section, it was not possible to assess NK1r immunoreactivity, and therefore the proportion of cells that expressed the receptor was not quantified.Table 8


A quantitative study of spinothalamic neurons in laminae I, III, and IV in lumbar and cervical segments of the rat spinal cord.

Al-Khater KM, Kerr R, Todd AJ - J. Comp. Neurol. (2008)

Retrograde labeling of lamina I neurons with fluorescent latex microspheres in parasagittal sections. The top row of images shows an example of a labeled lamina I neuron from C6 in experiment FLM3, and the bottom row shows a labeled neuron in L5 from experiment FLM2. In each case, separate images show the fluorescent latex microspheres (beads, red), NK1r (green) and NeuN (blue), with a merged image on the right. Note the presence of numerous beads in each neuron and that both neurons are NK1r-immunoreactive (arrow). Images are projections of seven (top row) or five (bottom row) confocal optical sections at 1-μm z-spacing. Scale bar = 20 μm in bottom right panel (applies to all).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2658017&req=5

fig11: Retrograde labeling of lamina I neurons with fluorescent latex microspheres in parasagittal sections. The top row of images shows an example of a labeled lamina I neuron from C6 in experiment FLM3, and the bottom row shows a labeled neuron in L5 from experiment FLM2. In each case, separate images show the fluorescent latex microspheres (beads, red), NK1r (green) and NeuN (blue), with a merged image on the right. Note the presence of numerous beads in each neuron and that both neurons are NK1r-immunoreactive (arrow). Images are projections of seven (top row) or five (bottom row) confocal optical sections at 1-μm z-spacing. Scale bar = 20 μm in bottom right panel (applies to all).
Mentions: Examples of retrogradely labeled neurons are shown in Figures 11 and 12, and quantitative data are provided in Table 8. The numbers of microspheres in labeled neurons varied considerably: only cells that contained 5 or more were considered to be retrogradely labeled, and most such cells contained more than 10 microspheres. The optical properties of Gel-Mount were not as good as those of Vectashield, and although fluorescent latex microspherescould be identified through the depth of the section, it was difficult to follow NK1r-immunoreactive profiles deep within the sections. In the C6 segment, lamina I was found to contain between 15 and 46 retrogradely labeled cells, whereas 5–10 retrogradely labeled lamina III/IV NK1r-immunoreactive cells were observed, of which 1–6 had dendrites that could be followed into the superficial dorsal horn (Fig. 12a). Because of the difficulty in following NK1r-immunoreactive dendrites in these sections, only those cells that had dorsal dendrites that entered lamina II in the superficial part of the same section could be unequivocally identified as belonging to this type. In the L5 segment, no retrogradely labeled cells were detected in laminae I or III/IV in experiment FLM1, whereas in experiments FLM 2 and FLM3, 4 and 5 lamina I cells (respectively) and 4 and 6 lamina III/IV NK1r cells (respectively) were seen. Dorsal dendrites of two of the lamina III/IV NK1r-immunoreactive cells in experiment FLM3 could be followed into the superficial dorsal horn, and one of these is illustrated in Figure 12b. Although many of the retrogradely labeled lamina I cells in C6 and L5 could be identified as NK1r-immunoreactive (Fig. 11), when the cell was in the deepest part of the section, it was not possible to assess NK1r immunoreactivity, and therefore the proportion of cells that expressed the receptor was not quantified.Table 8

Bottom Line: Our results suggest that there are 90 lamina I spinothalamic neurons per side in C7 and 15 in L4 and that some of those in C7 only project to PoT.We found that 85% of the lamina III/IV NK1r-immunoreactive neurons in C6 and 17% of those in L5 belong to the spinothalamic tract, and these apparently project exclusively to the caudal thalamus, including PoT.Because PoT projects to second somatosensory and insular cortices, our results suggest that these are major targets for information conveyed by both these populations of spinothalamic neurons.

View Article: PubMed Central - PubMed

Affiliation: Spinal Cord Group, Institute of Biomedical & Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom. a.todd@bio.gla.ac.uk

ABSTRACT
The major ascending outputs from superficial spinal dorsal horn consist of projection neurons in lamina I, together with neurons in laminae III-IV that express the neurokinin 1 receptor (NK1r) and have dendrites that enter the superficial laminae. Some neurons in each of these populations belong to the spinothalamic tract, which conveys nociceptive information via the thalamus to cortical areas involved in pain. A projection from the cervical superficial dorsal horn to the posterior triangular nucleus (PoT) has recently been identified. PoT is at the caudal end of the thalamus and was not included in injection sites in many previous retrograde tracing studies. We have injected various tracers (cholera toxin B subunit, Fluoro-Gold, and fluorescent latex microspheres) into the thalamus to estimate the number of spinothalamic neurons in each of these two populations, and to investigate their projection targets. Most lamina I and lamina III/IV NK1r-immunoreactive spinothalamic neurons in cervical and lumbar segments could be labeled from injections centered on PoT. Our results suggest that there are 90 lamina I spinothalamic neurons per side in C7 and 15 in L4 and that some of those in C7 only project to PoT. We found that 85% of the lamina III/IV NK1r-immunoreactive neurons in C6 and 17% of those in L5 belong to the spinothalamic tract, and these apparently project exclusively to the caudal thalamus, including PoT. Because PoT projects to second somatosensory and insular cortices, our results suggest that these are major targets for information conveyed by both these populations of spinothalamic neurons.

Show MeSH
Related in: MedlinePlus