The fundamental hypothesis guiding this proposal is that chronic treatments, known to enhance serotonergic modulation of respiratory motor output, strengthen respiratory synaptic pathways to spinal (phrenic) motoneurons, thereby improving respiratory function during recovery from spinal cord injury. In specific, we will investigate the effects of Chronic Intermittent Hypoxia (CIH) and spinal deafferentation via Cervical Dorsal Rhizotomy (CDR) on synaptic pathways to phrenic motoneuronsprior to acute spinal hemisection orfollowing chronic spinal hemisection. Our laboratory has previously shown that both CIH and CDR enhance serotonergic modulation of phrenic motor output, but appear to do so by different mechanisms. We have also shown that spinal serotonin receptor activation enhances both functional and ineffective (crossed-spinal) synaptic pathways in rats. Thus, we will apply these unique models of serotonin-dependent respiratory plasticity to test the hypothesis that they will restore respiratory drive to phrenic motoneurons on the injured (hemisected) side, and enhance respiratory drive to phrenic motoneurons on the uninjured (non-hemisected) side.
In Aims 1 and 2, we will test the hypotheses that pretreatment with either CIH or CDR enhances evoked and spontaneous phrenic activity in intact and crossed-spinal pathways in anesthetized rats. In the:next three aims, we will apply CIH following chronic spinal hemisection to test the hypotheses that CIH enhances evoked and spontaneous phrenic activity in anesthetized rats (Aim 3), restores ventilatory responses to chemoreceptor stimulation in unanesthetized rats (Aim 4), and increases ventral spinal concentrations of brain derived neurotrophic factor below the hemisection (Aim 5). This study provides an unprecedented opportunity to determine whether two unique experimental treatments restore respiratory motor function below a well-defined cervical spinal injury, and provides the basis for highly novel therapeutic approaches in the treatment of respiratory insufficiency following spinal cord injury.
|Agosto-Marlin, Ibis M; Nichols, Nicole L; Mitchell, Gordon S (2017) Adenosine-dependent phrenic motor facilitation is inflammation resistant. J Neurophysiol 117:836-845|
|Nichols, Nicole L; Satriotomo, Irawan; Allen, Latoya L et al. (2017) Mechanisms of Enhanced Phrenic Long-Term Facilitation in SOD1G93A Rats. J Neurosci 37:5834-5845|
|Navarrete-Opazo, A; Dougherty, B J; Mitchell, G S (2017) Enhanced recovery of breathing capacity from combined adenosine 2A receptor inhibition and daily acute intermittent hypoxia after chronic cervical spinal injury. Exp Neurol 287:93-101|
|Dale, Erica A; Fields, Daryl P; Devinney, Michael J et al. (2017) Phrenic motor neuron TrkB expression is necessary for acute intermittent hypoxia-induced phrenic long-term facilitation. Exp Neurol 287:130-136|
|Satriotomo, I; Nichols, N L; Dale, E A et al. (2016) Repetitive acute intermittent hypoxia increases growth/neurotrophic factor expression in non-respiratory motor neurons. Neuroscience 322:479-88|
|Devinney, Michael J; Nichols, Nicole L; Mitchell, Gordon S (2016) Sustained Hypoxia Elicits Competing Spinal Mechanisms of Phrenic Motor Facilitation. J Neurosci 36:7877-85|
|Navarrete-Opazo, A; Vinit, S; Dougherty, B J et al. (2015) Daily acute intermittent hypoxia elicits functional recovery of diaphragm and inspiratory intercostal muscle activity after acute cervical spinal injury. Exp Neurol 266:1-10|
|Devinney, Michael J; Fields, Daryl P; Huxtable, Adrianne G et al. (2015) Phrenic long-term facilitation requires PKC? activity within phrenic motor neurons. J Neurosci 35:8107-17|
|Fields, D P; Springborn, S R; Mitchell, G S (2015) Spinal 5-HT7 receptors induce phrenic motor facilitation via EPAC-mTORC1 signaling. J Neurophysiol 114:2015-22|
|Dougherty, Brendan J; Fields, Daryl P; Mitchell, Gordon S (2015) Mammalian target of rapamycin is required for phrenic long-term facilitation following severe but not moderate acute intermittent hypoxia. J Neurophysiol 114:1784-91|
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