Blood-brain barrier leakage after status epilepticus in rapamycin-treated rats I: Magnetic resonance imaging

Objective The mammalian target of rapamycin (mTOR) pathway has received increasing attention as a potential antiepileptogenic target. Treatment with the mTOR inhibitor rapamycin after status epilepticus reduces the development of epilepsy in a rat model. To study whether rapamycin mediates this effect via restoration of blood–brain barrier (BBB) dysfunction, contrast‐enhanced magnetic resonance imaging (CE‐MRI) was used to determine BBB permeability throughout epileptogenesis. Methods Imaging was repeatedly performed until 6 weeks after kainic acid–induced status epilepticus in rapamycin (6 mg/kg for 6 weeks starting 4 h after SE) and vehicle‐treated rats, using gadobutrol as contrast agent. Seizures were detected using video monitoring in the week following the last imaging session. Results Gadobutrol leakage was widespread and extensive in both rapamycin and vehicle‐treated epileptic rats during the acute phase, with the piriform cortex and amygdala as the most affected regions. Gadobutrol leakage was higher in rapamycin‐treated rats 4 and 8 days after status epilepticus compared to vehicle‐treated rats. However, during the chronic epileptic phase, gadobutrol leakage was lower in rapamycin‐treated epileptic rats along with a decreased seizure frequency. This was confirmed by local fluorescein staining in the brains of the same rats. Total brain volume was reduced by this rapamycin treatment regimen. Significance The initial slow recovery of BBB function in rapamycin‐treated epileptic rats indicates that rapamycin does not reduce seizure activity by a gradual recovery of BBB integrity. The reduced BBB leakage during the chronic phase, however, could contribute to the decreased seizure frequency in post–status epilepticus rats treated with rapamycin. Furthermore, the data show that CE‐MRI (using step‐down infusion with gadobutrol) can be used as biomarker for monitoring the effect of drug therapy in rats