Abstract WP231: Timecourse Characterization Of Neuronal Activation In The Contralesional Cortex After Stroke

Abstract

Introduction: Functional neuroimaging studies have reported increased activation in the contralesional cortex in both experimental and clinical settings of stroke. However, the dynamics of activation and neuronal subtypes involved is unclear. In this study we performed a time course analysis of neuronal activation and its subtypes in the contralesional cortex during post-stroke recovery using neuronal activity marker and cell type-specific markers. Methods: C57BL6 male mice (11-13 weeks old) underwent transient middle cerebral artery occlusion (MCAO, 30 minutes). Infarct was visualized by T2-weighted MRI and/or histology. Time course study used brains collected at PD1, 3, 7, 15, 21 and 28 and were processed for immunostaining using activity-dependent marker Early growth response 1 (Egr1). Egr1 positive cells were quantitatively assessed in the primary motor cortex (M1), pre-motor cortex (M2), and somatosensory cortex (SS) regions in the contralesional hemispheres. Cell type markers for NeuN (mature neurons), CaMKII and SATB2 (excitatory neurons), Parvalbumin (GABAergic neurons) and GFAP (astrocytes) were co-stained with Egr1 to identify its cell type specificity. Results: In the contralesional cortex, Egr1 predominantly co-localized with NeuN, indicating mature neurons. After stroke, contralesional cortical activity of Egr1 is detected at PD1-3 and peaks at PD7-15. Activity of Egr1 in contralesional cortex persisted at PD21-28 but begins to decrease in some regions. In-depth analysis of specific regions indicate that these changes occurred at contralesional M1, M2 and SS. Cell type co-localization analysis showed that Egr1 expressing cells are mostly colocalized with excitatory markers SATB2 and CaMKII but not inhibitory neuronal marker Parvalbumin, suggesting activated neurons in these contralesional cortical regions are mostly excitatory. Conclusion: Our results show that Egr1 expression is increased in excitatory neurons in the contralesional cortex after stroke, particularly in somatosensory and primary motor cortex. These data reveal dynamic changes of excitatory neuronal activity in the contralesional cortex post-stroke and highlight its involvement in post-stroke recovery.