Evaluation of Calcium-Mediated Persistent Inward Currents in Spinal Motor Neurons of Awake Behaving Rodents

Abstract

In order to test the natural synaptic input of motor neurons, we developed and tested a protocol for training rats to perform a voluntary motor behavior during which electromyography (EMG) recordings could be collected during natural synaptic input. Four rats were successfully trained to perform voluntary plantar flexion in conjunction with EMG recordings and another set of four naïve rats were used to gain insight into our surgical method of intrathecal catheter (ITC) implantation. All four naïve rats survived surgery with little to no complications, which prompted us to attempt implantation of two of the trained animals to no avail. To further evaluate this ITC method, verification methods including Lidocaine injections and laminectomy dissections were performed. Results were often confounding but provided useful knowledge about further use of this technique, which requires additional investigation and a larger sample size to make a definitive conclusion. Regardless, preliminary EMG data obtained with a separate cohort of rats, which were generously implanted by surgical specialist Kerry Gilbraith of the University of Arizona Department of Pharmacology, suggests that pharmacological blockade of persistent inward currents (PICs) with nifedipine results in a decreased firing rate of individual motor units (MUs) and compensatory MU recruitment to achieve the same target force. Again, further verification data is needed to rule out confounding factors associated with this data.