title: Accessory respiratory muscles enhance ventilation in ALS model mice and are activated by excitatory V2a neurons.
abstract: Inspiratory accessory respiratory muscles (ARMs) enhance ventilation when demands are high, such as during exercise and/or pathological conditions. Despite progressive degeneration of phrenic motor neurons innervating the diaphragm, amyotrophic lateral sclerosis (ALS) patients and rodent models are able to maintain ventilation at early stages of disease. In order to assess the contribution of ARMs to respiratory compensation in ALS, we examined the activity of ARMs and ventilation throughout disease progression in SOD1G93AALS model mice at rest using a combination of electromyography and unrestrained whole body plethysmography. Increased ARM activity, accompanied by increased ventilation, is observed beginning at the onset of symptoms. However, ARM recruitment fails to occur at rest at late stages of disease, even though the same ARMs are used for other behaviors. Using a chemogenetic approach, we demonstrate that a glutamatergic class of neurons in the brainstem and spinal cord, the V2a class, is sufficient to drive increased ARM activity at rest in healthy mice. Additionally, we reveal pathology in the medial reticular formation of the brainstem of SOD1G93Amice using immunohistochemistry and confocal imaging. Both spinal and brainstem V2a neurons degenerate in ALS model mice, accompanied by regional activation of astrocytes and microglia. These results establish inspiratory ARM recruitment as one of the compensatory mechanisms that maintains breathing at early stages of disease and indicate that V2a neuron degeneration may contribute to ARM failure at late stages of disease.
authors.affiliation: Division of Neurosurgery, Cincinnati Children's Hospital Medical Center, 3333 Burnet Avenue, Cincinnati, OH 45229.
authors.forename: Shannon H
authors.initials: SH
authors.lastname: Romer
authors.affiliation: Division of Neurosurgery, Cincinnati Children's Hospital Medical Center, 3333 Burnet Avenue, Cincinnati, OH 45229.
authors.forename: Kari
authors.initials: K
authors.lastname: Seedle
authors.affiliation: Division of Neurosurgery, Cincinnati Children's Hospital Medical Center, 3333 Burnet Avenue, Cincinnati, OH 45229.
authors.forename: Sarah M
authors.initials: SM
authors.lastname: Turner
authors.affiliation: Pain Research Center, Dept. of Anesthesiology, University of Cincinnati Medical Center, 231 Albert Sabin Way, Cincinnati, OH 45267.
authors.forename: Jie
authors.initials: J
authors.lastname: Li
authors.affiliation: Pain Research Center, Dept. of Anesthesiology, University of Cincinnati Medical Center, 231 Albert Sabin Way, Cincinnati, OH 45267.
authors.forename: Mark L
authors.initials: ML
authors.lastname: Baccei
authors.affiliation: Division of Neurosurgery, Cincinnati Children's Hospital Medical Center, 3333 Burnet Avenue, Cincinnati, OH 45229; Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, 3333 Burnet Avenue, Cincinnati, OH 45229. Electronic address: Steven.Crone@cchmc.org.
authors.forename: Steven A
authors.initials: SA
authors.lastname: Crone
mesh_terms: D000690:Amyotrophic Lateral Sclerosis / Q000235:genetics / Q000473:pathology*; D000818:Animals; D015703:Antigens, CD / Q000378:metabolism; D015214:Antigens, Differentiation, Myelomonocytic / Q000378:metabolism; D001933:Brain Stem / Q000473:pathology; D003024:Clozapine / Q000031:analogs & derivatives / Q000494:pharmacology; D004195:Disease Models, Animal; D005786:Gene Expression Regulation / Q000187:drug effects / Q000235:genetics*; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007395:Interneurons / Q000502:physiology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000235:genetics; D051379:Mice; D008822:Mice, Transgenic; D050480:Plasma Membrane Neurotransmitter Transport Proteins / Q000235:genetics / Q000378:metabolism; D043587:Receptor, Muscarinic M3; D011976:Receptors, Muscarinic / Q000235:genetics / Q000378:metabolism; D012119:Respiration / Q000235:genetics; D012132:Respiratory Muscles / Q000503:physiopathology*; D013116:Spinal Cord / Q000473:pathology*; D013482:Superoxide Dismutase / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D000097382:CD68 Molecule
chemical_list: D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D003024:Clozapine; D005904:Glial Fibrillary Acidic Protein; D018398:Homeodomain Proteins; D050480:Plasma Membrane Neurotransmitter Transport Proteins; D043587:Receptor, Muscarinic M3; D011976:Receptors, Muscarinic; D013482:Superoxide Dismutase; D014157:Transcription Factors; C067980:CD68 antigen, human; D000097382:CD68 Molecule; C000595896:CHRM3 protein, human; C088975:Vsx2 protein, mouse; C109415:SOD1 G93A protein; C079149:clozapine N-oxide
keywords: Amyotrophic lateral sclerosis; Motor neuron disease; Neurodegeneration; Respiratory circuit; Respiratory muscle; Respiratory plasticity; V2a neuron; Ventilation failure