Techniques and Approaches: From Molecules to Circuits to Whole Animal Physiology
The goal of the Crone Lab is to develop novel treatment strategies targeting neural circuits to restore breathing following injury or disease. The lab uses a variety of techniques to identify neurons important for the control of respiratory muscles and identify molecules in those neurons that have the potential to serve as drug targets to improve breathing.
RNA sequencing is used to better understand the diversity of gene expression within spinal neurons and determine how they are affected by disease and injury. A combination of transgenic mouse and viral tools (DREADDs, neuron ablation, optogenetics, etc.) are used to alter the activity or functions of specific classes of neurons in order to determine how they contribute to the control of respiratory muscles in healthy animals as well as following disease or injury.
Implantable transmitters are used to measure electromyography (EMG) to measure the activity of respiratory muscles and plethysmography to assess ventilation in awake or anesthetized mice.
Our current research focuses on restoring breathing after spinal cord injury, control of accessory respiratory muscles and preventing sudden death in epilepsy (SUDEP).
Harnessing Spinal Network Plasticity to Restore Diaphragm Function Following Spinal Cord Injury
Cervical spinal cord injuries can disrupt communication between the brainstem centers that generate the breathing rhythm and respiratory motor neurons in the spinal cord, leading to paralysis of breathing muscles. Some (but not all) patients will spontaneously recover breathing function over time, due in part to changes in spinal circuits that control respiratory motor neurons. We found that altering the firing activity of one class of spinal neuron (V2a neurons) can restore inspiratory activity to a previously paralyzed diaphragm in a mouse model of cervical spinal cord injury. Current work focuses on identifying genes expressed by V2a neurons that are important for respiratory circuit plasticity and could serve as drug targets to improve breathing following injury.
Control of Accessory Respiratory Muscles
Although the diaphragm is the primary muscle used for breathing, additional muscles in the chest, neck and abdomen (accessory respiratory muscles) are recruited to enhance ventilation when we run, cough, sigh or take deep breaths. These muscles are also critical for maintaining ventilation and preventing respiratory infections when diaphragm function is impaired, as occurs in patients with neuromuscular disease or following spinal cord injury. We found that the V2a class of neurons activates accessory respiratory muscles when needed as well as keeps them inactive at rest. They also discovered that these neurons degenerate in a mouse model of amyotrophic lateral sclerosis (ALS), suggesting that the loss of compensation by accessory respiratory muscles may contribute to ventilatory failure at late stages of disease. The lab is currently working to further elucidate circuits that control respiratory muscles in order to prevent ventilator dependence following disease or injury.
Preventing Respiratory Deficits Leading to Sudden Death in Epilepsy (SUDEP)
Each year, about 1 in 1,000 people with epilepsy die of SUDEP. The incidence climbs to more than 1 in 150 for epilepsy patients with uncontrolled seizures. The causes are unknown but are thought to be due to cardiorespiratory dysfunction. In collaboration with the Gross Lab, we are investigating breathing abnormalities observed in a mouse model of SUDEP using implantable telemetry devices to chronically measure diaphragm activity and electroencephalography. Their goal is to determine which signaling pathway(s) and brain regions are responsible for the breathing abnormalities and whether drugs targeting specific pathways can prevent breathing abnormalities and SUDEP.