The autonomic brainstem generates and modifies breathing rhythm by integrating inputs from chemo- and mechanosensors in the viscera while coordinating descending outputs from higher CNS structures. Hypoglossal motoneurons (XII MNs) receive inputs from respiratory premotor neurons in the medulla. Previous studies in rodents have demonstrated significant changes in breathing control during the first three weeks of life, with a sensitive period at 10 to 13 days post-birth (P10–P13) characterized by pronounced changes in neurotransmitters, receptors, excitation-inhibition balance, and breathing. However, age-dependent morphological changes of XII MNs during the first three weeks post-birth and especially during this sensitive period, have not been thoroughly studied. In this study, we comprehensively characterized and quantified the postnatal morphological changes in rat XII MNs. We hypothesized that morphological changes occur in XII MN morphology and arbor complexity corresponding to the functionally-defined sensitive period observed at P10–P13. To test this hypothesis, we used innovative statistical approaches to quantify and compare developmental changes in Golgi-Cox stained XII MNs at nine postnatal ages between P1–P21. Additionally, we performed 3D reconstructions of the neurons importing these geometries into the modeling environment NEURON to simulate the biophysical properties of XII MNs. Soma size increased ~40% from P1 to P21, with no significant change in shape. However, dendritic arborization increased in extent and complexity with branching of neurons significantly increasing from P1 through P13, with the greatest increase at P10–P13 based on the Sholl method. Three age groups 1) P1–P5, 2) P7–P12, and 3) P13–P21 were found as possible windows of development. We also found that at specific ages certain parameters such as soma size and dendritic complexity were non-normally distributed. I found support for differences in the density of selected voltage-gated ion channels with age and correlations between passive electrophysiological properties and morphology. Although a direct relationship was not found between morphology and the active properties, I did find support for an indirect relationship. Our detailed characterization of XII MN morphological development establishes a foundation for the study and elucidation of morphological changes caused by maternal and perinatal conditions using a rigorous approach.
","abstract_html":"<p>The autonomic brainstem generates and modifies breathing rhythm by integrating inputs from chemo- and mechanosensors in the viscera while coordinating descending outputs from higher CNS structures. Hypoglossal motoneurons (XII MNs) receive inputs from respiratory premotor neurons in the medulla. Previous studies in rodents have demonstrated significant changes in breathing control during the first three weeks of life, with a sensitive period at 10 to 13 days post-birth (P10–P13) characterized by pronounced changes in neurotransmitters, receptors, excitation-inhibition balance, and breathing. However, age-dependent morphological changes of XII MNs during the first three weeks post-birth and especially during this sensitive period, have not been thoroughly studied. In this study, we comprehensively characterized and quantified the postnatal morphological changes in rat XII MNs. We hypothesized that morphological changes occur in XII MN morphology and arbor complexity corresponding to the functionally-defined sensitive period observed at P10–P13. To test this hypothesis, we used innovative statistical approaches to quantify and compare developmental changes in Golgi-Cox stained XII MNs at nine postnatal ages between P1–P21. Additionally, we performed 3D reconstructions of the neurons importing these geometries into the modeling environment NEURON to simulate the biophysical properties of XII MNs. Soma size increased ~40% from P1 to P21, with no significant change in shape. However, dendritic arborization increased in extent and complexity with branching of neurons significantly increasing from P1 through P13, with the greatest increase at P10–P13 based on the Sholl method. Three age groups 1) P1–P5, 2) P7–P12, and 3) P13–P21 were found as possible windows of development. We also found that at specific ages certain parameters such as soma size and dendritic complexity were non-normally distributed. I found support for differences in the density of selected voltage-gated ion channels with age and correlations between passive electrophysiological properties and morphology. Although a direct relationship was not found between morphology and the active properties, I did find support for an indirect relationship. Our detailed characterization of XII MN morphological development establishes a foundation for the study and elucidation of morphological changes caused by maternal and perinatal conditions using a rigorous approach.</p>","abstract_has_math":false,"creators":["Williams, Paul Allen"],"institution":null,"degree_name":"Doctor of Philosophy (PhD)","degree_level":"Dissertation","degree_discipline":"Basic Sciences","degree_department":null,"school":null,"contributors":["Wilson, Christopher G.","Bellinger, Denise L.","Buchholz, John N.","Oberg, Kerby C.","Wilson, Sean M."],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2018,"date_issued":"2018-06-01T07:00:00Z","date_published":"2018-06-01T07:00:00Z","updated_at":"2026-07-24T02:52:52Z","subjects":["Medical Physiology","Medical Sciences","Medicine and Health Sciences","Cranial Nerves; Brain Stem; Rats; Motor Neurons","Autonomic Brainstem; Breathing Rhythm; Morphology"],"languages":["English"],"rights":["This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights."],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://scholarsrepository.llu.edu/etd/521","outbound_label":"Repository record","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Wilson, Christopher G.","Bellinger, Denise L.","Buchholz, John N.","Oberg, Kerby C.","Wilson, Sean M."]},{"key":"dc:creator","label":"Author","values":["Williams, Paul Allen"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"thesis:degree_discipline","label":"Discipline","values":["Basic Sciences"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Doctor of Philosophy (PhD)"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Medical Physiology","Medical Sciences","Medicine and Health Sciences","Cranial Nerves; Brain Stem; Rats; Motor Neurons","Autonomic Brainstem; Breathing Rhythm; Morphology"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["English"]},{"key":"dc:rights","label":"Dc Rights","values":["This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights."]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://scholarsrepository.llu.edu/etd/521"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["The autonomic brainstem generates and modifies breathing rhythm by integrating inputs from chemo- and mechanosensors in the viscera while coordinating descending outputs from higher CNS structures. Hypoglossal motoneurons (XII MNs) receive inputs from respiratory premotor neurons in the medulla. Previous studies in rodents have demonstrated significant changes in breathing control during the first three weeks of life, with a sensitive period at 10 to 13 days post-birth (P10–P13) characterized by pronounced changes in neurotransmitters, receptors, excitation-inhibition balance, and breathing. However, age-dependent morphological changes of XII MNs during the first three weeks post-birth and especially during this sensitive period, have not been thoroughly studied. In this study, we comprehensively characterized and quantified the postnatal morphological changes in rat XII MNs. We hypothesized that morphological changes occur in XII MN morphology and arbor complexity corresponding to the functionally-defined sensitive period observed at P10–P13. To test this hypothesis, we used innovative statistical approaches to quantify and compare developmental changes in Golgi-Cox stained XII MNs at nine postnatal ages between P1–P21. Additionally, we performed 3D reconstructions of the neurons importing these geometries into the modeling environment NEURON to simulate the biophysical properties of XII MNs. Soma size increased ~40% from P1 to P21, with no significant change in shape. However, dendritic arborization increased in extent and complexity with branching of neurons significantly increasing from P1 through P13, with the greatest increase at P10–P13 based on the Sholl method. Three age groups 1) P1–P5, 2) P7–P12, and 3) P13–P21 were found as possible windows of development. We also found that at specific ages certain parameters such as soma size and dendritic complexity were non-normally distributed. I found support for differences in the density of selected voltage-gated ion channels with age and correlations between passive electrophysiological properties and morphology. Although a direct relationship was not found between morphology and the active properties, I did find support for an indirect relationship. Our detailed characterization of XII MN morphological development establishes a foundation for the study and elucidation of morphological changes caused by maternal and perinatal conditions using a rigorous approach.
"]},{"key":"dc:title","label":"Title","values":["Changes in the Morphology of Hypoglossal Motor Neurons in the Brainstem of Developing Rats"]}]}],"canonical_facts":{"dc:contributor":["Wilson, Christopher G.","Bellinger, Denise L.","Buchholz, John N.","Oberg, Kerby C.","Wilson, Sean M."],"dc:creator":["Williams, Paul Allen"],"dc:description.abstract":["The autonomic brainstem generates and modifies breathing rhythm by integrating inputs from chemo- and mechanosensors in the viscera while coordinating descending outputs from higher CNS structures. Hypoglossal motoneurons (XII MNs) receive inputs from respiratory premotor neurons in the medulla. Previous studies in rodents have demonstrated significant changes in breathing control during the first three weeks of life, with a sensitive period at 10 to 13 days post-birth (P10–P13) characterized by pronounced changes in neurotransmitters, receptors, excitation-inhibition balance, and breathing. However, age-dependent morphological changes of XII MNs during the first three weeks post-birth and especially during this sensitive period, have not been thoroughly studied. In this study, we comprehensively characterized and quantified the postnatal morphological changes in rat XII MNs. We hypothesized that morphological changes occur in XII MN morphology and arbor complexity corresponding to the functionally-defined sensitive period observed at P10–P13. To test this hypothesis, we used innovative statistical approaches to quantify and compare developmental changes in Golgi-Cox stained XII MNs at nine postnatal ages between P1–P21. Additionally, we performed 3D reconstructions of the neurons importing these geometries into the modeling environment NEURON to simulate the biophysical properties of XII MNs. Soma size increased ~40% from P1 to P21, with no significant change in shape. However, dendritic arborization increased in extent and complexity with branching of neurons significantly increasing from P1 through P13, with the greatest increase at P10–P13 based on the Sholl method. Three age groups 1) P1–P5, 2) P7–P12, and 3) P13–P21 were found as possible windows of development. We also found that at specific ages certain parameters such as soma size and dendritic complexity were non-normally distributed. I found support for differences in the density of selected voltage-gated ion channels with age and correlations between passive electrophysiological properties and morphology. Although a direct relationship was not found between morphology and the active properties, I did find support for an indirect relationship. Our detailed characterization of XII MN morphological development establishes a foundation for the study and elucidation of morphological changes caused by maternal and perinatal conditions using a rigorous approach.
"],"dc:identifier":["https://scholarsrepository.llu.edu/etd/521"],"dc:language":["English"],"dc:rights":["This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights."],"dc:subject":["Medical Physiology","Medical Sciences","Medicine and Health Sciences","Cranial Nerves; Brain Stem; Rats; Motor Neurons","Autonomic Brainstem; Breathing Rhythm; Morphology"],"dc:title":["Changes in the Morphology of Hypoglossal Motor Neurons in the Brainstem of Developing Rats"],"thesis:degree_discipline":["Basic Sciences"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Doctor of Philosophy (PhD)"]},"updated_at":"2026-07-24T02:52:52Z"}