Introduction: The mechanisms of functional recovery after stroke are thought to be based on structural and functional changes in brain circuits. Deciphering these changes at the synaptic level is key to understanding the re-organization of the synaptic circuitry. Quantitative information about such synapse rearrangements after stroke has been inadequate however, due to the technical limitations of available methodologies. Here we describe the use of array tomography, a new high-resolution proteomic imaging method, to determine the composition of glutamate and GABA synapses in the post-stroke mouse brain.
Methods: A cortical lesion was induced in 12-week-old C57BL/6J male mice using the distal middle cerebral artery occlusion model of ischemia. Small tissue sections were removed from the peri-infarct cortex and ribbons of serial ultrathin sections were obtained using an ultramicrotome. Ribbons were stained with antibodies for the synaptic markers. Analysis of the resultant staining pattern was used to identify subtypes of glutamatergic and GABAergic synapses. In addition, whole-cell patch clamp recordings from acute neocortical brain slices were performed to evaluate functions of neocortical pyramidal neurons in peri-infarct cortex.
Results: At 1 week post-stroke, an increase in the density and proportion of GABAergic synapses was observed in layer 5 of the peri-infarct cortex. Overall, total synapse number did not differ between stroke-injured and naïve animals. Changes in GABA synapses were transient and returned to basal levels by 1 month. These changes were only found in layer 5 but not layer 2/3. Furthermore, GABAA receptor-mediated currents were enhanced in layer 5 pyramidal neurons at 1 week post-stroke.
Conclusions: These results provide new information about the organization of synaptic circuitry and its plasticity after stroke. They suggest that stroke induces an increased expression in functional GABAA receptors and cortical plasticity changes after stroke are layer-specific.
Patient Care: We suggest homeostatic mechanisms during the initial stages of stroke recovery re-establish the activation of stroke-affected areas through both structural and functional changes to circuits.
Understanding the mechanisms of cortical plasticity can give some information about indentifying therapeutic targets for stroke patients.
Learning Objectives: By the conclusion of this session, participants should be able to understand the importance of detecting mechanisms, that re-establish the activation of stroke-affected areas through both structural and functional changes to circuits during the stroke recovery.