Activation of groups of excitatory neurons in the mammalian spinal cord or hindbrain evokes locomotion

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Abstract

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.

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Figure 1: Schematic representation of the BAC Vglut2-ChR2-YFP construct and resulting expression of ChR2-YFP in hindbrain and spinal cord.
Figure 2: ChR2-YFP is reliably expressed in excitatory neurons and neuronal classes that express Vglut2 in the spinal cord.
Figure 3: Spinal cord ChR2-YFP neurons depolarize in response to blue light.
Figure 4: Optical activation of Vglut2-expressing cells in the spinal cord generates coordinated locomotor-like activity.
Figure 5: Optical activation of the lower hindbrain is sufficient to generate locomotor-like activity in the lumbar spinal cord.
Figure 6: Blocking glutamatergic synapses in the hindbrain does not prevent light-induced hindbrain-evoked locomotor-activity.

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Acknowledgements

We thank K. Deisseroth for providing us with the ChR2 construct, D. Engblom for technical assistance with BAC cloning and the Karolinska Center for Transgenic Technologies for pronuclear injection. This work was supported by grants from the US National Institutes of Health (R01NS040795-08), the European Union (SPINAL CORD REPAIR), the National Science Foundation (0701166 to K.J.D.), and by the Swedish Medical Research Council, the Karolinska Institutet's foundation for support of graduate students (M.H.) and postdocs (L.B.), Söderbergs Foundation, and Friends of Karolinska Intitutet.

Author information

All of the authors contributed to the design of the experiments. M.H. and L.B. built the mouse construct and performed the expression validation. M.H., K.J.D. and O.K. performed the electrophysiological experiments and analyzed the results. All of the authors contributed to the drafting and writing of the paper.

Correspondence to Ole Kiehn.

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Hägglund, M., Borgius, L., Dougherty, K. et al. Activation of groups of excitatory neurons in the mammalian spinal cord or hindbrain evokes locomotion. Nat Neurosci 13, 246–252 (2010) doi:10.1038/nn.2482

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