Accessory respiratory muscles enhance ventilation in ALS model mice and are activated by excitatory V2a neurons

• Published in: Experimental neurology Vol. 287; no. Pt 2; pp. 192 - 204
• Main Authors: Romer, Shannon H., Seedle, Kari, Turner, Sarah M., Li, Jie, Baccei, Mark L., Crone, Steven A.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.01.2017
• Subjects: Amyotrophic lateral sclerosis; Amyotrophic Lateral Sclerosis - genetics; Amyotrophic Lateral Sclerosis - pathology; Animals; Antigens, CD - metabolism; Antigens, Differentiation, Myelomonocytic - metabolism; Brain Stem - pathology; Clozapine - analogs & derivatives; Clozapine - pharmacology; Disease Models, Animal; Gene Expression Regulation - drug effects; Gene Expression Regulation - genetics; Glial Fibrillary Acidic Protein - metabolism; Homeodomain Proteins - genetics; Homeodomain Proteins - metabolism; Humans; Interneurons - physiology; Male; Membrane Potentials - drug effects; Membrane Potentials - genetics; Mice; Mice, Transgenic; Motor neuron disease; Neurodegeneration; Plasma Membrane Neurotransmitter Transport Proteins - genetics; Plasma Membrane Neurotransmitter Transport Proteins - metabolism; Receptor, Muscarinic M3; Receptors, Muscarinic - genetics; Receptors, Muscarinic - metabolism; Respiration - genetics; Respiratory circuit; Respiratory muscle; Respiratory Muscles - physiopathology; Respiratory plasticity; Spinal Cord - pathology; Superoxide Dismutase - genetics; Superoxide Dismutase - metabolism; Transcription Factors - genetics; Transcription Factors - metabolism; V2a neuron; Ventilation failure; mRF; TV; WBP; Ventilation failure; Motor neuron disease; ALS; MV; Amyotrophic lateral sclerosis; PIF; SOD1; V2a neuron; Respiratory plasticity; Respiratory muscle; Neurodegeneration; ARM; Respiratory circuit; EMG
• ISSN: 0014-4886; 1090-2430
• DOI: 10.1016/j.expneurol.2016.05.033

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 SOD1G93A ALS 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 SOD1G93A mice 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. •Accessory respiratory muscles are recruited early in disease in a mouse model of ALS•Accessory muscles are functional but not used for breathing at late disease stages•V2a neurons are sufficient to drive accessory respiratory muscle activity•V2a neurons degenerate in mouse models of ALS