Martin Hägglund, Lotta Borgius, Kimberly J Dougherty, Ole Kiehn

Central pattern generators (CPGs) are spinal neuronal networks required for locomotion. Glutamatergic neurons have been implicated as being important for intrinsic rhythm generation in the CPG and for the command signal for initiating locomotion, although this has not been demonstrated directly. We used a newly generated vesicular glutamate transporter 2-channelrhodopsin2-yellow fluorescent protein (Vglut2-ChR2-YFP) mouse to directly examine the functional role of glutamatergic neurons in rhythm generation and initiation of locomotion. This mouse line expressed ChR2-YFP in the spinal cord and hindbrain. ChR2-YFP was reliably expressed in Vglut2-positive cells and YFP-expressing cells could be activated by light. Photo-stimulation of either the lumbar spinal cord or the caudal hindbrain was sufficient to both initiate and maintain locomotor-like activity. Our results indicate that glutamatergic neurons in the spinal cord are critical for initiating or maintaining the rhythm and that activation of hindbrain areas containing the locomotor command regions is sufficient to directly activate the spinal locomotor network.