A system for postural experiments and its effects on behavior in the rat model of spinal cord injury
Authors:   , Meyers Michael C. , Moxon Karen Anne 
Published: July 2024

Spinal cord injury is a condition in which the nerve tissue in the spinal canal is damaged, causing a loss of sensory and motor function below the level of the injury. In order to improve quality of life for people with spinal cord injury, a treatment to re-enable them to walk is needed. Several therapies have successfully produced locomotor-like movements of the legs after spinal cord injury, but they do not address the loss of balance control without which locomotor movements are of questionable value. To determine how balance is maintained and how this changes after spinal cord injury, experiments have been performed in which the subjects must maintain their body position and orientation in spite of a perturbation. These experiments have shown that there is a neural postural control system which controls the ground reaction force to maintain a stable body position, and that the basic elements of this system are located in the spinal cord with some involvement of brainstem and cortical structures. A recent experiment aimed to investigate the response of the motor cortex to a lateral tilting task and how this response changes after injury, in hopes of finding signals that could be used to drive a brain machine interface. The system used in the experiment mentioned above tilted rats in their frontal planes and recorded the response of the motor cortex. To relate this activity to the output of the postural control system, it was necessary to modify the system to record parameters of the ground reaction force. To evaluate this relationship in an animal with spinal cord injury, a weight support device and harness are required to suspend the hip girdle in the air, allowing the animal to stand and preventing it from falling off the platform. This is concerning because the postural control system being investigated achieves the same goal. Therefore there was a need to evaluate whether the use of a harness and weight support system changed the parameters of the ground reaction force distribution in an animal on the tilting platform. The first specific aim of this project was to make the modifications that enabled the tilting platform system to record ground reaction force data. The second specific aim was to determine if and how forces applied to the animal by the harness and weight support device changed the ground reaction force and center of pressure trajectory during tilting. The first aim was accomplished by incorporating uniaxial single-point load cells into the platform to measure the normal force. These added mass to the system and necessitated the selection of a more powerful motor. A new LabVIEW VI was also written to control the system. The system was tested and satisfied the required resolution, accuracy, and time-locking between force and neural data acquisition. The second aim was accomplished by recording ground reaction force data during tilting for rats attached to the weight support device, in the harness without the weight support device, and without the harness. It was found that the harness alone had only mild effects on the center of pressure and normal forces. The weight support device had a substantial impact, causing the center of pressure to resemble that of a passive mass on the platform. This suggested that the animals maintained their body positions and orientations using the weight support device rather than using ground reaction forces and engaging their postural control systems. Therefore, before the system can be used to investigate changes to postural systems after spinal cord injury, a new method of supporting the weight of the animals without artificially maintaining their body position is needed.