Research PaperReversible recovery of neuronal structures depends on the degree of neuronal damage after global cerebral ischemia in mice

- Recovery of neuronal structures is critically dependent on the duration of ischemia.
- Ischemic damage progressively spreads to deeper dendritic shafts.
- The timeframe for recovery of dendritic structures is within 3-6 h after stroke onset.
- Reversible recovery of neurons may determine the therapeutic time window for stroke.

It has been observed by in vivo imaging that damaged neuronal structures can be reversibly restored after ischemic insults with the application of timely therapeutic interventions. However, what degree of neuronal damage can be restored and the time frame for reversible recovery of neuronal structures remain unclear. Here, transcranial two-photon imaging, histological staining and electron microscopy were used to investigate the reversible recovery of neuronal structures from dendrites to soma after different durations of global cerebral ischemia in mice. Intravital imaging revealed that the damage to dendritic structures was reversible when ischemia time was < 1 h, but they became difficult to restore after > 3 h of ischemia. Data from fixed YFP brain slice and Golgi staining indicated that the damage of dendritic structures progressively extended to deeper dendritic shafts with the extension of ischemia time. Furthermore, longer duration of ischemia caused an increasing number of degenerating neurons. Importantly, significant chromatin margination and karyopyknosis of neuron were observed after 6 h of ischemia. These data suggested that neuronal structures could be reversibly restored when ischemia time was < 1 h, but irreversible and progressive damage to neurons occurred with longer duration of ischemia. Consistently, behavioral performance of post-ischemic animals experienced an ischemia time-dependent recovery. Taken together, our data suggested that recovery of neuronal structures following ischemia was dependent on the duration of ischemia, and prevention of neuronal loss is a key target for therapeutic interventions in ischemic stroke.