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Chemosensitive Neurons of the Locus Coeruleus and the Nucleus Tractus Solitarius: Three Dimensional Morphology and Association with the Vasculature

Graham, Cathy D.
http://rave.ohiolink.edu/etdc/view?acc_num=wright1409665728

Abstract Details

2014, Doctor of Philosophy (PhD), Wright State University, Biomedical Sciences PhD.
We studied the 3 dimensional structure of LC and cNTS neurons from neonatal rats. Neurons were identified as either chemosensitive or nonchemosensitive based on their firing rate response to hypercapnia, using whole-cell patch clamping and were passively loaded with Lucifer Yellow. The identified, loaded neurons were reconstructed and analyzed using Neurolucida Neuron Tracing Software. Chemosensitive LC neurons have less rounded soma than nonchemosensitive neurons, and they have dendrites arising from two poles to produce a fusiform appearance. The dendritic branches extend a greater distance from the soma of chemosensitive than nonchemosensitive neurons. Conversely, chemosensitive cNTS neurons were found to have ovoid multipolar somas with compact, complex arborization while nonchemosensitive neurons had bipolar somas with projections arising from opposite poles separated by ~ 180º. Chemosensitive LC neurons and cNTS neurons have at least one projection that makes a closer approach to the floor of the 4th ventricle than do nonchemosensitive neurons from both regions, but on average this closest approach is still greater than 50 microns. These data indicate that projection to the surface of the brainstem is not necessary for the chemosensitive response in the LC and the cNTS. To evaluate regional vascularity and neuronal populations, neurons and blood vessels were labeled using immunohistochemical techniques. Neurons were labeled with NeuN and blood vessels with Isolectin-GS-IB4 (a marker for endothelial cells). Confocal microscopy was used to collect images through 50 µm sections. Image J analysis of the confocal projections revealed that in the LC there is a higher density of blood vessels in the chemosensitive dorsal and intermediate regions compared to the nonchemosensitive ventral region of the LC. Interestingly, the dorsal and intermediate zones of the LC have a very high percentage of chemosensitive neurons while the ventral zone has mostly nonchemosensitive neurons, suggesting greater perfusion of chemosensitive neurons. In the cNTS, the densest neutrophil was observed in the medial area with less neuronal density in the commissural and lateral areas. The overall cNTS regional microvascular density was more homogenous and considerably less dense than that of the LC. Finally, we found that capillaries make direct contacts with the somata of chemosensitive neurons but not with the somata of nonchemosensitive neurons. In the cNTS, there is no pattern of association of blood vessels with individual neuronal structures though some contact was observed. Our findings demonstrate that there is not a single neuronal morphology typical of chemosensitive neurons but that there are morphological distinctions between chemosensitive vs. nonchemosensitive neurons which may be region specific. Our data indicate that association between the dendritic arbor and the surface of the floor of the fourth ventricle is not necessary for chemosensing in these two areas. The demonstrated close association between the somas of chemosensitive neurons and capillaries in the LC is consistent with chemosensitive signaling being based in the soma of LC neurons. When compared to cNTS, our findings do not support the hypothesis that this is a neuronal/vascular arrangement requisite for chemosensitive areas of the brainstem. Our data provide anatomically accurate information for the construction of physiologically relevant, multi-compartment computational models of chemosensitive neurons.
Robert Putnam, Ph.D. (Advisor)
Adrain Corbett, Ph.D. (Committee Member)
Lynn Hartzler, Ph.D. (Committee Member)
James Olson, Ph.D. (Committee Member)
Christopher Wyatt, Ph.D. (Committee Member)
223 p.
Biomedical Research; Morphology; Neurosciences; Physiology
chemosensitive; morphology; central chemosensitivity; locus coeruleus, LC, nucleus tractus solitarius; NTS; chemoreceptor; CO2 sensor; vasculature; blood vessels; capillaries; blood brain barrier; pH; blood gases

Recommended Citations

Citations

  • Graham, C. D. (2014). Chemosensitive Neurons of the Locus Coeruleus and the Nucleus Tractus Solitarius: Three Dimensional Morphology and Association with the Vasculature [Doctoral dissertation, Wright State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=wright1409665728

    APA Style (7th edition)

  • Graham, Cathy. Chemosensitive Neurons of the Locus Coeruleus and the Nucleus Tractus Solitarius: Three Dimensional Morphology and Association with the Vasculature . 2014. Wright State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=wright1409665728.

    MLA Style (8th edition)

  • Graham, Cathy. "Chemosensitive Neurons of the Locus Coeruleus and the Nucleus Tractus Solitarius: Three Dimensional Morphology and Association with the Vasculature ." Doctoral dissertation, Wright State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=wright1409665728

    Chicago Manual of Style (17th edition)

wright1409665728
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This open access ETD is published by Wright State University and OhioLINK.