The responses of ventrolateral medullary neurons to hypoxia
Nolan, Patrick Christopher
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Permalink
https://hdl.handle.net/2142/19759
Description
Title
The responses of ventrolateral medullary neurons to hypoxia
Author(s)
Nolan, Patrick Christopher
Issue Date
1995
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, Neuroscience
Biology, Animal Physiology
Language
eng
Abstract
These studies investigated the electrophysiological responses of individual ventrolateral medullary (VLM) neurons during brief exposures of hypoxia. Extracellular recordings of VLM neurons in anesthetized rats demonstrated a large proportion (64%) which were excited during brief hypoxia (10% O$\sb2$, 60 sec). A similar percentage of VLM neurons (65%) were similarly stimulated in subjects initially peripherally chemodenervated and barodenervated. The majority of VLM neurons in intact and denervated animals possessed basal discharges correlated with the cardiovascular and/or respiratory cycles. A large proportion of VLM neurons (73%) were also stimulated in an in vitro brainslice preparation during hypoxia (10% O$\sb2$/5% CO$\sb2$/85% N$\sb2$ or 5% CO$\sb2$/95% N$\sb2$, 90 sec). Pharmacological blockade of synaptic transmission did not alter these responses. Whole-cell patch recordings demonstrated the hypoxic excitatory response is mediated by a moderate depolarization (4-8 mV) and an increased membrane conductance. Patch recordings from neonatal and juvenile rats also demonstrated that neonatal neurons were less likely to display the excitatory response, and when this response was encountered, it was significantly attenuated compared to juvenile responses. VLM neurons were also investigated for their hypoxic responses in vitro following an initial period of in vivo hypoxic acclimatization (4-5 days or 9-10 days, 10% O$\sb2$). Neurons from subjects exposed to the short acclimatization showed a greater excitatory response to hypoxia. The neuronal responses from animals exposed to the longer acclimatizing period were similar to controls. Together these findings demonstrate that a significant population of neurons in an important cardiorespiratory integration region is rapidly excited during brief hypoxic exposures. This response probably plays a role in modulating the systemic cardiorespiratory response to hypoxia in the intact animal. These findings also indicate that, like the cardiorespiratory response to hypoxia, the neonatal response of VLM neurons to hypoxia is diminished. Further, the hypoxic induced excitation of VLM neurons is affected in the early period of acclimatization corresponding with other initial alterations in central nervous system activity. The responses of these neurons may be important in mediating the cardiovascular and respiratory responses observed during systemic hypoxia.
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