Development and Mechanism of Oxygen Sensitivity in Caudal Hypothalamic Neurons
Horn, Eric Michael
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Permalink
https://hdl.handle.net/2142/82542
Description
Title
Development and Mechanism of Oxygen Sensitivity in Caudal Hypothalamic Neurons
Author(s)
Horn, Eric Michael
Issue Date
2000
Doctoral Committee Chair(s)
Waldrop, Tony G.
Department of Study
Neuroscience
Discipline
Neuroscience
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Animal Physiology
Language
eng
Abstract
The goals of the studies described in this thesis were to elucidate the development of the hypoxic responses of rat caudal hypothalamic neurons and to determine the specific membrane properties responsible for these responses. Male Sprague-Dawley rats aged postnatal day 3 (P3) through P56 were exposed to hypoxia for a period of 3 hours. When compared to their normoxic counterparts, the rats exposed to hypoxia displayed a significant increase in the density of caudal hypothalamic neurons expressing the protein Fos. This increase, however, was not apparent until P12 and continued throughout P56. Peripheral chemoreceptor input was not required for this increase since a similar increase in the density of Fos protein induced by hypoxia was observed following section of the carotid sinus nerves in a subset of rats. Similarly, caudal hypothalamic neurons from more mature rats were more likely to respond to a brief period of hypoxia when compared to cells from immature rats in a brain slice preparation. The response of these cells to hypoxia was a depolarization and increased firing frequency that was due to a sustained inward current. Interestingly, this inward current response was no different in magnitude between neurons from immature and mature rats. Pharmacological analyses demonstrated that this inward current response was due to sodium and not calcium current. This sodium current was then studied in greater detail in acutely dissociated caudal hypothalamic neurons from mature rats. Whole-cell patch clamp recordings determined that both the fast-inactivating and persistent sodium current were significantly increased during hypoxia in these neurons. Taken together, hypoxia activates caudal hypothalamic neurons in conscious rats throughout development in a manner consistent with the development of the respiratory responses to hypoxia. This activation involves an inward current that is prevalent in a greater portion of mature caudal hypothalamic neurons. Enhancement of two types of sodium current is the likely mechanism of this hypoxia-induced inward current and most likely underlies the depolarization and increased firing frequency observed in these cells during hypoxia. This developmental activation of caudal hypothalamic neurons likely modulates the development of the respiratory responses to hypoxia.
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