The objective of this project is to determine the cellular signals for plasticity in central nervous system components of ventilatory chemoreflexes during Chronic Sustained Hypoxia (CSH). The significance of this research is that it addresses a fundamental but unanswered question in pulmonary medicine: What are the neural mechanisms that increase ventilatory drive and enhance the reflex control of arterial O2 and CO2 during chronic hypoxemia from pulmonary disease? More specifically, we will test the hypothesis that some of the same molecular signals and cellular mechanisms described by others to explain Long Term Facilitation (LTF) with intermittent hypoxia (IH) also contribute to plasticity in ventilatory chemoreflexes during CSH. There has been tremendous progress on mechanisms of LTF recently, which allows us to efficiently test evaluate the model in CSH. Comparing and contrasting plasticity in CSH and IH is significant by allowing us to systematically evaluate potential therapeutic targets for the most important causes of chronic hypoxemia, namely COPD causing CSH and sleep disordered breathing causing IH. First we will establish that the molecular signals for enhanced glutamatergic neurotransmission reported for phrenic LTF in anesthetized rats occur with ventilatory LTF after IH in conscious mice. Then we will measure those molecular signals in mice after CSH and use pharmacology and conditional gene deletion to test their physiological significance for ventilatory acclimatization to CSH. Drugs or Cre-recombinase expressed by adeno-associated virus will be microinjected intrathecally to the spinal cord or stereotaxically in the brainstem of wildtype or transgenic mice to manipulate putative signals for plasticity in different populations of respiratory neurons. Experiments are designed to compare and contrast plasticity with IH vs. CSH. For example, we hypothesize that TrkB phosphorylation is a signal for plasticity in both IH and CSH but BDNF is only a signal in IH. Also, we hypothesize that increases in Reactive Oxygen Species (ROS) with both IH and CSH are an important signal for plasticity and we will measure the time course of ROS changes with different patterns of hypoxia and alter them to test physiological significance. Finally, we will test the hypothesis that CSH causes similar molecular signals for plasticity in a transgenic mouse model of emphysema (conditional deletion of the vascular endothelial growth factor gene in the lung). This is our first step towards addressing the important question of whether the neural plasticity studied in healthy animals acclimatized to environmental hypoxia occurs in diseases with chronic hypoxemia, or if chronic lung disease also involves abnormal plasticity.
This project studies changes in the reflex control of breathing caused by two different patterns of decreased blood oxygen: chronic intermittent hypoxia, which occurs with sleep disordered breathing and apnea, and chronic sustained hypoxia, which occurs with chronic obstructive pulmonary disease. We will use pharmacology and genetic engineering to determine similarities and differences in molecular signals for changes in the neural control of breathing with different patterns of hypoxia in conscious mice. Also, we will use a mouse model of chronic lung disease to distinguish the independent effects of low oxygen from other effects of lung disease.
|Pamenter, Matthew E; Carr, J Austin; Go, Ariel et al. (2014) Glutamate receptors in the nucleus tractus solitarius contribute to ventilatory acclimatization to hypoxia in rat. J Physiol 592:1839-56|
|Nichols, Nicole L; Powell, Frank L; Dean, Jay B et al. (2014) Substance P differentially modulates firing rate of solitary complex (SC) neurons from control and chronic hypoxia-adapted adult rats. PLoS One 9:e88161|
|Powell, Frank L (2012) Measuring the respiratory chemoreflexes in humans by J. Duffin. Respir Physiol Neurobiol 181:44-5|
|Popa, Dan; Fu, Zhenxing; Go, Ariel et al. (2011) Ibuprofen blocks time-dependent increases in hypoxic ventilation in rats. Respir Physiol Neurobiol 178:381-6|
|Hoshijima, Masahiko; Hayashi, Takeharu; Jeon, Young E et al. (2011) Delta-sarcoglycan gene therapy halts progression of cardiac dysfunction, improves respiratory failure, and prolongs life in myopathic hamsters. Circ Heart Fail 4:89-97|
|Wilkinson, Katherine A; Fu, Zhenxing; Powell, Frank L (2011) Ventilatory effects of substance P-saporin lesions in the nucleus tractus solitarii of chronically hypoxic rats. Am J Physiol Regul Integr Comp Physiol 301:R343-50|
|Powell, Frank L (2010) Studying biological responses to global change in atmospheric oxygen. Respir Physiol Neurobiol 173 Suppl:S6-12|
|Wilkinson, Katherine A; Huey, Kimberly; Dinger, Bruce et al. (2010) Chronic hypoxia increases the gain of the hypoxic ventilatory response by a mechanism in the central nervous system. J Appl Physiol 109:424-30|
|Nichols, Nicole L; Wilkinson, Katherine A; Powell, Frank L et al. (2009) Chronic hypoxia suppresses the CO2 response of solitary complex (SC) neurons from rats. Respir Physiol Neurobiol 168:272-80|
|Nichols, Nicole L; Mulkey, Daniel K; Wilkinson, Katherine A et al. (2009) Characterization of the chemosensitive response of individual solitary complex neurons from adult rats. Am J Physiol Regul Integr Comp Physiol 296:R763-73|
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