468 Visualizing Plasticity of the Dorsal Column Nuclei Following Spinal Cord Injury Using Two Photon Microscopy

INTRODUCTION: The dorsal column nuclei represent the first relay point in the somatosensory pathways from the spinal cord to the cerebral cortex. Despite its obvious significance, however, we do not have a complete picture of the precise representation of the lower extremity in this nucleus, and how such representation can be modified following lesions. METHODS: 10 mice underwent suboccipital craniotomy with implantation of imaging window. In vivo imaging was performed using a two-photon microscope based on a movable objective microscope system controlled by ScanImage software. Images were collected at a depth of 0–250 μm from the dura surface for nucleus gracilis and cuneatus. For image analysis, movement artifacts were corrected. Then, the regions of interest (ROIs) containing the neurons were drawn manually, and the pixel values within each ROI were summed to estimate the fluorescence of the individual neuron. RESULTS: Two photon microscopy was able to reproduce a functional cellular map of the nucleus gracilis and cuneatus. Our data demonstrate precise but dynamic representation of sensory stimuli in the brainstem sensory nucleus. We discovered that the spatial representation of the individual figures are intermingled. Furthermore, the neural responses to forelimb stimulation emerged within the nucleus gracilis following T3 spinal cord injury, suggesting brainstem plasticity occurs early in the post-injury period. CONCLUSIONS: This work provides a proof of concept for real-time imaging of brainstem structures, including the dorsal column medial lemniscus pathway. Our data demonstrate precise but dynamic representation of sensory stimuli in the brainstem sensory nucleus that can be leveraged for future applications.