Cervical spinal cord injury (SCI) disrupts neural pathways to respiratory motor neurons, diminishing breathing capacity. Since even modest breathing impairment greatly increases susceptibility to life-threatening lung infections, restorin lost breathing capacity will improve the quality and duration of life. With funding from this MERIT Award, we discovered that repetitive acute intermittent hypoxia (rAIH) triggers plasticity in spared neural pathways to respiratory motor neurons, thereby restoring lost breathing capacity. We propose to extend these findings by addressing fundamental gaps in our knowledge concerning mechanisms of rAIH-induced functional recovery in rats with cervical SCI. The fundamental hypothesis guiding this proposal is that completely different cellular mechanisms underlie rAIH-induced functional recovery in early (<4 weeks) versus chronic SCI (>4 weeks). We propose that rAIH elicits plasticity via adenosinergic mechanisms in early SCI, but serotonin-dependent (adenosine-constrained) mechanisms in chronic SCI. This surprising idea will change the way we think about respiratory plasticity following SCI. Indeed, the realization that mechanisms giving rise to rAIH-induced plasticity and functional recovery are time-dependent will profoundly alter our ability to harness rAIH as a therapeutic intervention in humans with respiratory insufficiency due to chronic SCI. Since AIH-induced respiratory plasticity is impaired by systemic inflammation and constrained by cross-talk inhibition from competing mechanisms of phrenic motor facilitation, we hypothesize that functional outcomes may be improved by diminishing these factors in chronic (not early) SCI. We propose to investigate rAIH-induced functional recovery with a highly novel, multi-disciplinary approach including: 1) plethysmography to assess breathing capacity;2) EMG telemetry of respiratory muscles;3) flow cytometry to assess changes in identified respiratory motor neurons;4) immuno-fluorescence to assess key proteins in situ;and 5) manipulation of respiratory motor neuron gene expression via RNA interference in vivo.
Three specific aims are proposed to test the hypotheses that: 1) adenosine- (early) and serotonin-dependent (chronic) mechanisms dominate rAIH- induced functional recovery at different times post-injury;a corollary is that spinal adenosine 2A receptor inhibition augments rAIH-induced functional recovery in chronic (not early) SCI;2) the contributions of different inspiratory muscles shift with time post-injury; and 3) systemic inflammation impairs rAIH-induced functional recovery in chronic (not early) SCI. Although rAIH has potential to be a safe, non-invasive treatment for SCI- induced respiratory impairment, any rational translation of this promising therapy will require detailed understanding of its underlying mechanisms, including complexities such as shifting mechanisms with time post-injury and factors that degrade its therapeutic efficacy. rAIH represents a promising new strategy to enhance function in patients with chronic SCI, where the prognosis for functional gains is bleak.

Public Health Relevance

Cervical spinal injury disrupts neural pathways in the spinal cord, often leading to death from inadequate breathing capacity. The prognosis for meaningful functional recovery is bleak. Our goal is to understand simple procedures to stimulate spinal cord plasticity as a means of strengthening spared neural pathways to the spinal nerve cells that drive breathing, thereby restoring lost breathing capacity.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
2R01HL069064-11A1
Application #
8654482
Study Section
Special Emphasis Panel (ZRG1-CVRS-M (03))
Program Officer
Laposky, Aaron D
Project Start
2002-01-01
Project End
2018-01-31
Budget Start
2014-02-15
Budget End
2015-01-31
Support Year
11
Fiscal Year
2014
Total Cost
$719,953
Indirect Cost
$241,579
Name
University of Wisconsin Madison
Department
Biology
Type
Schools of Veterinary Medicine
DUNS #
161202122
City
Madison
State
WI
Country
United States
Zip Code
53715
Navarrete-Opazo, A; Mitchell, G S (2014) Recruitment and plasticity in diaphragm, intercostal, and abdominal muscles in unanesthetized rats. J Appl Physiol (1985) 117:180-8
Huxtable, A G; MacFarlane, P M; Vinit, S et al. (2014) Adrenergic ?? receptor activation is sufficient, but not necessary for phrenic long-term facilitation. J Appl Physiol (1985) 116:1345-52
Dale, Erica A; Mitchell, Gordon S (2013) Spinal vascular endothelial growth factor (VEGF) and erythropoietin (EPO) induced phrenic motor facilitation after repetitive acute intermittent hypoxia. Respir Physiol Neurobiol 185:481-8
Devinney, Michael J; Huxtable, Adrianne G; Nichols, Nicole L et al. (2013) Hypoxia-induced phrenic long-term facilitation: emergent properties. Ann N Y Acad Sci 1279:143-53
Huxtable, A G; Smith, S M C; Vinit, S et al. (2013) Systemic LPS induces spinal inflammatory gene expression and impairs phrenic long-term facilitation following acute intermittent hypoxia. J Appl Physiol (1985) 114:879-87
Nichols, N L; Punzo, A M; Duncan, I D et al. (2013) Cervical spinal demyelination with ethidium bromide impairs respiratory (phrenic) activity and forelimb motor behavior in rats. Neuroscience 229:77-87
Johnson, Stephen M; Turner, Sara M; Huxtable, Adrianne G et al. (2012) Isolated in vitro brainstem-spinal cord preparations remain important tools in respiratory neurobiology. Respir Physiol Neurobiol 180:1-7
Mitchell, Gordon S; Terada, Jiro (2011) Should we standardize protocols and preparations used to study respiratory plasticity? Respir Physiol Neurobiol 177:93-7
Baker-Herman, T L; Bavis, R W; Dahlberg, J M et al. (2010) Differential expression of respiratory long-term facilitation among inbred rat strains. Respir Physiol Neurobiol 170:260-7
Vinit, Stephane; Lovett-Barr, Mary Rachael; Mitchell, Gordon S (2009) Intermittent hypoxia induces functional recovery following cervical spinal injury. Respir Physiol Neurobiol 169:210-7

Showing the most recent 10 out of 22 publications