Using Optogenetics and Fictive Locomotion to Investigate the Effects of Inhibiting Renshaw Cells on Normal Locomotion in P3 Mice

Sammanfattning: The circuit of recurring inhibition between motor neurons and Renshaw cells in the spinal cord has been known for around 70 years, though no determined function has been outlined as of yet. Renshaw cells are thought to be part of the central pattern generator in the spinal cord establishing them as an important part of the animal’s locomotive properties. In this study we aimed to investigate the role of Renshaw cells in locomotion with the help of optogenetics and electrophysiology. Halorhodopsin was inserted into the genome of mice and driven to expression with Cre recombinase in Renshaw cells. The spinal cord of P3 mice was extracted and by inducing fictive locomotion with appropriate neurotransmitters we could inhibit the Renshaw cells in action with a green laser, opening the halorhodopsin channels for Cl- ions. In previous experiments where the ability of Renshaw cells to release inhibitory neurotransmitters was inactivated, no effect was observed in either behavioral experiments or electrophysiological experiments. In a system where the effect of Renshaw cells was knocked out acutely with optogenetics there was no discernible change in fictive locomotion cycle length, frequency or amplitude. Nor was there an effect on alternation. The access of light to the Renshaw cells area might have been limited during the experiment considering the angle of light delivery and strength of the laser. Furthermore, the maturity of Renshaw cells at P3, the exclusive ability of the marker used to target Renshaw cells and the observed nature of neonatal inhibitory neurons acting as excitatory neurons could all be called into question about whether they contributed to these results or not.