The ability to manipulate specific neuronal populations of the spinal cord following spinal cord injury (SCI) could prove highly beneficial for rehabilitation in patients through maintaining and strengthening still existing neuronal connections and/or facilitating the formation of new connections. A non-invasive and highly specific approach to neuronal stimulation is bioluminescent-optogenetics (BL-OG), where genetically expressed light emitting luciferases are tethered to light sensitive channelrhodopsins (luminopsins, LMO); neurons are activated by the addition of the luciferase substrate coelenterazine (CTZ). This approach utilizes ion channels for current conduction while activating the channels through the application of a small chemical compound, thus allowing non-invasive stimulation and recruitment of all targeted neurons. Rats were transduced in the lumbar spinal cord with AAV2/9 to express the excitatory LMO3 under control of a pan-neuronal or motor neuron-specific promoter. A day after contusion injury of the thoracic spine, rats received either CTZ or vehicle every other day for 2 weeks. Activation of either neuron population below the level of injury significantly improved locomotor recovery lasting beyond the treatment window. Utilizing histological and gene expression methods we identified neuronal plasticity as a likely mechanism underlying the functional recovery. These findings provide a foundation for a rational approach to spinal cord injury rehabilitation, thereby advancing approaches for functional recovery after SCI. Summary Bioluminescent optogenetic activation of spinal neurons results in accelerated and enhanced locomotor recovery after spinal cord injury in rats.
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Ipsilateral and Contralateral Interactions in Spinal Locomotor Circuits Mediated by V1 Neurons: Insights from Computational Modeling
We describe and analyze a computational model of neural circuits in the mammalian spinal cord responsible for generating and shaping locomotor-like oscillations. The model represents interacting populations of spinal neurons, including the neurons that were genetically identified and characterized in a series of previous experimental studies. Here, we specifically focus on the ipsilaterally projecting V1 interneurons, their possible role in the spinal locomotor circuitry, and their involvement in the generation of locomotor oscillations. The proposed connections of these neurons and their involvement in different neuronal pathways in the spinal cord allow the model to reproduce the results of optogenetic manipulations of these neurons under different experimental conditions. We suggest the existence of two distinct populations of V1 interneurons mediating different ipsilateral and contralateral interactions within the spinal cord. The model proposes explanations for multiple experimental data concerning the effects of optogenetic silencing and activation of V1 interneurons on the frequency of locomotor oscillations in the intact cord and hemicord under different experimental conditions. Our simulations provide an important insight into the organization of locomotor circuitry in the mammalian spinal cord.
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- Award ID(s):
- 2113069
- NSF-PAR ID:
- 10344221
- Date Published:
- Journal Name:
- International Journal of Molecular Sciences
- Volume:
- 23
- Issue:
- 10
- ISSN:
- 1422-0067
- Page Range / eLocation ID:
- 5541
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Irrespective of the many strategies focused on dealing with spinal cord injury (SCI), there is still no way to restore motor function efficiently or an adequate regenerative therapy. One promising method that could potentially prove highly beneficial for rehabilitation in patients is to re-engage specific neuronal populations of the spinal cord following SCI. Targeted activation may maintain and strengthen existing neuronal connections and/or facilitate the reorganization and development of new connections. BioLuminescent-OptoGenetics (BL-OG) presents an avenue to non-invasively and specifically stimulate neurons; genetically targeted neurons express luminopsins (LMOs), light-emitting luciferases tethered to light-sensitive channelrhodopsins that are activated by adding the luciferase substrate coelenterazine (CTZ). This approach employs ion channels for current conduction while activating the channels through treatment with the small molecule CTZ, thus allowing non-invasive stimulation of all targeted neurons. We previously showed the efficacy of this approach for improving locomotor recovery following severe spinal cord contusion injury in rats expressing the excitatory luminopsin 3 (LMO3) under control of a pan-neuronal and motor-neuron-specific promoter with CTZ applied through a lateral ventricle cannula. The goal of the present study was to test a new generation of LMOs based on opsins with higher light sensitivity which will allow for peripheral delivery of the CTZ. In this construct, the slow-burn Gaussia luciferase variant (sbGLuc) is fused to the opsin CheRiff, creating LMO3.2. Taking advantage of the high light sensitivity of this opsin, we stimulated transduced lumbar neurons after thoracic SCI by intraperitoneal application of CTZ, allowing for a less invasive treatment. The efficacy of this non-invasive BioLuminescent-OptoGenetic approach was confirmed by improved locomotor function. This study demonstrates that peripheral delivery of the luciferin CTZ can be used to activate LMOs expressed in spinal cord neurons that employ an opsin with increased light sensitivity.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/ijms23105541
