Intermittent Hypoxia-Induced Spinal Inflammation Impairs Respiratory Motor Plasticity by a Spinal p38 MAP Kinase-Dependent Mechanism.
Inflammation is characteristic of most clinical disorders that challenge the neural control of breathing. Since inflammation modulates neuroplasticity, we studied the impact of inflammation caused by prolonged intermittent hypoxia on an important form of respiratory plasticity, acute intermittent hypoxia (three, 5 min hypoxic episodes, 5 min normoxic intervals) induced phrenic long-term facilitation (pLTF). Because chronic intermittent hypoxia elicits neuroinflammation and pLTF is undermined by lipopolysaccharide-induced systemic inflammation, we hypothesized that one night of intermittent hypoxia (IH-1) elicits spinal inflammation, thereby impairing pLTF by a p38 MAP kinase-dependent mechanism. pLTF and spinal inflammation were assessed in anesthetized rats pretreated with IH-1 (2 min hypoxia, 2 min normoxia; 8 h) or sham normoxia and allowed 16 h for recovery. IH-1 (1) transiently increased IL-6 (1.5 ± 0.2-fold; p = 0.02) and inducible nitric oxide synthase (iNOS) (2.4 ± 0.4-fold; p = 0.01) mRNA in cervical spinal homogenates, (2) elicited a sustained increase in IL-1β mRNA (2.4 ± 0.2-fold; p < 0.001) in isolated cervical spinal microglia, and (3) abolished pLTF (-1 ± 5% vs 56 ± 10% in controls; p < 0.001). pLTF was restored after IH-1 by systemic NSAID administration (ketoprofen; 55 ± 9%; p < 0.001) or spinal p38 MAP kinase inhibition (58 ± 2%; p < 0.001). IH-1 increased phosphorylated (activated) p38 MAP kinase immunofluorescence in identified phrenic motoneurons and adjacent microglia. In conclusion, IH-1 elicits spinal inflammation and impairs pLTF by a spinal p38 MAP kinase-dependent mechanism. By targeting inflammation, we may develop strategies to manipulate respiratory motor plasticity for therapeutic advantage when the respiratory control system is compromised (e.g., sleep apnea, apnea of prematurity, spinal injury, or motor neuron disease).
Department of Comparative Biosciences, University of Wisconsin, Madison, Wisconsin 53706, and University of Oregon, Eugene, Oregon 97403.
Adrianne G
AG
Huxtable
Department of Comparative Biosciences, University of Wisconsin, Madison, Wisconsin 53706, and.
Stephanie M C
SM
Smith
Department of Comparative Biosciences, University of Wisconsin, Madison, Wisconsin 53706, and.
Timothy J
http://orcid.org/0000-0003-0995-3644
TJ
Peterson
Department of Comparative Biosciences, University of Wisconsin, Madison, Wisconsin 53706, and.
Jyoti J
JJ
Watters
Department of Comparative Biosciences, University of Wisconsin, Madison, Wisconsin 53706, and gsmitche@phhp.ufl.edu.
Gordon S
GS
Mitchell
D000818:Animals; D000893:Anti-Inflammatory Agents / Q000627:therapeutic use; D039481:CD11b Antigen / Q000378:metabolism; D016207:Cytokines / Q000235:genetics / Q000378:metabolism; D004195:Disease Models, Animal; D005786:Gene Expression Regulation / Q000187:drug effects; D000860:Hypoxia / Q000150:complications*; D007660:Ketoprofen / Q000627:therapeutic use; D008297:Male; D017628:Microglia / Q000187:drug effects / Q000378:metabolism; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology*; D009187:Myelitis / Q000150:complications* / Q000188:drug therapy / Q000209:etiology*; D009473:Neuronal Plasticity / Q000187:drug effects / Q000502:physiology*; D052247:Nitric Oxide Synthase Type II / Q000235:genetics / Q000378:metabolism; D010791:Phrenic Nerve / Q000503:physiopathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012120:Respiration Disorders / Q000209:etiology*; D013997:Time Factors; D014628:Vagotomy; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*
D000893:Anti-Inflammatory Agents; D039481:CD11b Antigen; D016207:Cytokines; D007660:Ketoprofen; D052247:Nitric Oxide Synthase Type II; D048051:p38 Mitogen-Activated Protein Kinases
inflammation; long-term facilitation; microglia; motor neuron; plasticity; spinal cord