Key resources table.

Physiological mechanisms of the key hyperacute (0–24 hours) stage of stroke are poorly understood, hampering the development of new therapies. Synaptic plasticity has been strongly implicated in early stages of neurodegenerative and neurodevelopmental disorders, yet its relevance in early stroke remains unclear. Here, we describe the emergence of distinct region-specific forms of synaptic remodeling following middle cerebral artery occlusion in rats, arising within the critical 4-hour period. Synapses within the severely ischemic core region were rapidly lost, while those in the mildly ischemic penumbra, albeit largely structurally intact, were functionally diminished. In contrast, the contralateral cortex exhibited increased synaptic staining and synaptic vesicle cycling. Systemic pharmacological blockade of NMDA-type glutamate receptors abolished contralateral synaptic increase and exacerbated synaptic decline in the penumbra. Proteomic and transcriptomic analyses showed that cross-brain synaptic plasticity is independent of local gene expression and revealed metabolic rearrangement and synaptic downregulation in the penumbra. These findings identify brain-wide synaptic rebalancing as a potential mechanism for rapid functional compensation in hyperacute stroke, highlighting the extent of brain response to acute perturbation.