(K-428) A Chronic Study of Neuroplasticity in a Mouse Stroke Model Using Ultraflexible Neural Threads

Introduction:: In the field of neural engineering, ultraflexible nanoelectronic thread electrodes (NETs) developed at the Xie and Luan Labs have emerged as a highly effective device for longitudinal neural recording due to their superior biocompatibility.1 The NETs accomplish this through an orders-of-magnitude improvement in mechanical compliance and seamless integration with neural tissue, providing stable electrophysiological recordings of individual neurons over months. In my group's project, these advanced capabilities are being utilized to perform a longitudinal study of a stroke neuroplasticity model in the mouse barrel cortex. Specifically, our group aims to understand the changes in the neural populations and their activity of the area surrounding the stroke site (the peri-infarct region) in the weeks to months after the stroke. Previous literature that has worked to characterize neural population after stroke have used methodology that is inherently limited, such as 2-Photon imaging with low temporal resolution.2 We believe our analysis will create a more complete picture of the populational changes in neurons by utilizing the longitudinal, high spatial and temporal resolution recordings of NETs. This improved understanding of population level neural activity in the time after stroke can open up the doors to therapeutics that can improve the recovery of neural function in the peri-infarct.

Materials and Methods:: To perform this study, we have a developed a robust experimentation pipeline that utilizes the spatial whisker mapping of the mouse barrel cortex to understand the neural response of the space surrounding the target barrel. We implemented our ultraflexible neural thread technology (NETs) in a targeted region (C2 barrel). Four shanks, each bearing 32 electrodes, were embedded in the barrels surrounding the target barrel, each providing a comprehensive coverage of a cortical column. Photothrombotic stroke was induced a month post cranial surgery, and was confined to the C2 whisker barrel using a digital micromirror device and a precise 532 nm laser beam.

The study involved longitudinal neural recording of the peri-infarct region, capturing baseline data before and up to two months post stroke. Mechanically stimulating the C2 whisker enabled the monitoring of neural responses from surrounding neurons. (Figure 1) Using the software DeepLabCut, the behavioral videos of whisker stimulation were processed to train a model predicting whisker location, calculating angular velocity during the experiment. We utilized this model to effectively filter out trials with high levels of spontaneous whisking activity during baseline recordings. (Figure 2) A multi-modal optical imaging platform, incorporating Laser Speckle Contrast and Hyperspectral Intrinsic Optical Imaging, was utilized to cross correlate with electrophysiology recordings, providing a comprehensive understanding of the neural response post-stroke.

Data-processing pipeline consisted of spike-sorting with MountainSort, cluster merging using phy, and cell-type distinction using CellExplorer.

Results, Conclusions, and Discussions::
Results

Our results demonstrate significant changes in the neural populations and their activity in multiple ways. We characterized the population plasticity of different cell types after the stroke, where we found that inhibitory fast spiking/PV interneurons exhibit the strongest recovery post-stroke relative to pyramidal and wide interneurons (Figures 3 and 4). We have corroborated with previous studies that there is a significant increase in neural inhibition post-stroke.3 Neural adaptation is found to be significantly higher in the peri-infarct 7 days post-stroke using an adaptation index observing the response to the first whisker deflection relative to subsequent whisker deflections (Figure 5). Neural burst firing in pyramidal neurons using the bursting index is significantly higher >14 days post-stroke (Figure 5).




Conclusions




Our investigation provides a novel approach to the study of the neural response following stroke, employing advanced NET technology that enables longitudinal high temporal and spatial resolution. We utilized these capabilities to demonstrate significant changes in cell-type specific populations, neural adaptation, and bursting. Our findings elucidate complex changes in neural populations and mechanisms, and have the potential to guide future therapeutic strategies aimed at optimizing post-stroke recovery.




Discussions




Our study has significantly advanced our understanding of neural population dynamics in the peri-infarct region following a stroke, opening new avenues for exploring therapeutics to enhance recovery of neural function in the stroke-affected areas. Our results underscore the significant role of plasticity in cell-type specific populations in post-stroke recovery, corroborating previous findings on the increase in neural inhibition through increased GABA synapses during stroke recovery. Specifically, the strong recovery exhibited by inhibitory fast spiking/PV interneurons suggests that these cell types might be crucial targets in future therapeutic interventions aimed at optimizing stroke recovery. NETs enable us to look at neural mechanisms like adaptation and bursting due to their high temporal resolution. Our results on neural burst firing and adaptation has implications for the understanding of stroke recovery, but more research is needed to further understand the functional significance of these neural mechanisms in relation to stroke. Our future research will delve deeper into neural circuits and network connectivity.




Acknowledgements (Optional): :

References (Optional): : 1. Zhao, Z., Zhu, H., Li, X. et al. Ultraflexible electrode arrays for months-long high-density electrophysiological mapping of thousands of neurons in rodents. Nat. Biomed. Eng 7, 520–532 (2023).

2. Zeiger, W.A., Marosi, M., Saggi, S. et al. Barrel cortex plasticity after photothrombotic stroke involves potentiating responses of pre-existing circuits but not functional remapping to new circuits. Nat Commun 12, 3972 (2021). https://doi.org/10.1038/s41467-021-24211-8

3. Hiu, T., Farzampour, Z., Paz, J. T., Wang, E. H., Badgely, C., Olson, A., Micheva, K. D., Wang, G., Lemmens, R., Tran, K. V., Nishiyama, Y., Liang, X., Hamilton, S. A., O'Rourke, N., Smith, S. J., Huguenard, J. R., Bliss, T. M., & Steinberg, G. K. (2016). Enhanced phasic GABA inhibition during the repair phase of stroke: a novel therapeutic target. Brain : a journal of neurology, 139(Pt 2), 468–480. https://doi.org/10.1093/brain/awv360