Determining the efficacy of therapeutic interventions after stroke from cell specific functional connectomes - PROJECT SUMMARY/ABSTRACT Understanding circuit-level maneuvers that affect brain plasticity will inform the design of targeted interventions after stroke. Experiments outlined in this proposal will determine the contributions of excitatory/inhibitory circuits on brain repair processes after focal ischemia, and how changes in behavioral performance relate to cell-specific changes in connectivity. Stroke causes direct structural damage to local brain circuitry and indirect disruption of global networks resulting in behavioral deficits spanning multiple domains. Stroke recovery is associated with functional brain reorganization, a process involving the formation of new or alternative circuits. Along with behavioral recovery, damaged regions remap to adjacent tissue while patterns of resting-state functional connectivity (RS-FC) within and across resting-state networks gradually renormalize. While local and global changes in functional brain organization are consistently observed during recovery, how these processes relate to the underlying neuronal circuitry supporting recovery of function is unknown. This knowledge gap exists partially because stimulus-evoked and resting-state patterns reflect ensemble activity from many cell types, and patterns of RS-FC can be orchestrated through indirect pathways. Understanding how disconnected inhibitory and excitatory circuits reintegrate into global networks to support recovery requires examination of neural network connectivity structure as it evolves with neuroanatomical markers of circuit repair. While an integrated mechanism relating cellular plasticity with network plasticity has yet to be established, inhibitory circuits have been shown to play a key role. Stroke disrupts the brain’s balance of excitation and inhibition. Restoring this balance through non-invasive brain stimulation techniques can improve recovery. However, treatment efficacy using these methods is extremely varied, partially due to the imprecision and indiscriminate activation or inhibition of all cells near the stimulated site. Parvalbumin interneurons (PV-INs) are the most prevalent of all GABAergic interneurons, play key roles in shaping excitability over long distances, and regulate functional brain rhythms reflected in coherent patterns of RS-FC. Though their role in post-stroke plasticity is unknown, PV-INs are known to mediate several other forms of activity-dependent plasticity, making them compelling candidates for affecting repair processes after stroke. Using optogenetic targeting and wide field optical imaging of cortical calcium dynamics in awake mice, we will establish functional connectomes of excitatory (CamK2a-based) and inhibitory (PV-based) circuits and how they evolve following focal ischemia (Aim 1). We will utilize the well- characterized motor-barrel network in the mouse to directly test the influence of activity in cortical excitatory/inhibitory nodes exhibiting strong (Aim 2) or weak (Aim 3) inter- or intra-hemispheric connectivity with perilesional tissue, and how these manipulations affect neuroanatomical markers of circuit repair. At the conclusion of this grant, we will determine the contributions of CamK2a/PV circuits on post-stroke recovery, and further understand the components of connectivity restoration required for more complete behavioral recovery.
