Abstracts

Rationale: Postischemic seizure occurs in 3-5% of the cerebral ischemic patients. Diabetes doubles the risk for postischemic seizure development. The molecular mechanism under this clinical relevant phenomenon remains unknown. Inhibition of mammalian target of rapamycin (mTOR) has been employed as a therapeutic approach in treating various types of epileptic seizures. The objectives of this study are to examine the preventive effects of rapamycin on postischemic seizures in diabetic rats and to explore the underlying molecular mechanisms.Methods: Fifty-two male Wistar rats were divided in to non-diabetic (n=16), diabetic (n=20) and diabetic+rapamycin treatment (n=16) groups. Diabetes was induced in male Wistar rats (250-300 g) by streptozotocin intraperitoneal injection. Transient forebrain ischemia of 10 min duration was induced 2 months after the induction of diabetes. Rapamycin 6mg/kg was ip injected 7 days prior to the induction of ischemia. Animals were observed for seizure incidence after reperfusion and brain tissues were sampled at 16 h of reperfusion. All experiments were conducted in accordance with the NIH Guide for the Care and Use of Laboratory Animals and approved the institutional IACUC.Results: The results showed that none of the 16 non-diabetic ischemic rats developed seizure up to 7 days of reperfusion. In contrast, 7 out of 10 diabetic rats developed postischemic epileptic seizures after 1-16 h of reperfusion. Seizures were presented as generalized tonic-clonic type. Rapamycin treatment blocked the development of postischemic seizure in 5 out 6 of rats (Figure 1). Histopathological studies revealed that diabetic ischemia caused severe neuronal death in the hippocampal CA1, CA3 and dentate gyrus regions, thalamus and cerebral cortex at 16 h of recovery. Rapamycin significantly reduced the neuronal death and TUNEL positive neurons. Protein analyses demonstrated (Figure 2) that diabetes mellitus per se significantly increased the phosphorylation of mTOR and P70S6K, but not p-S6. Ischemia reduced the levels of p-mTOR and p-P70S6K, but significantly increased the p-S6, comparing to diabetic control. Rapamycin suppressed the levels of p-mTOR, p-P70S6K, and p-S6 in both diabetic control and diabetic ischemic rats. Further, diabetic ischemia significantly increased the protein levels of p-ERK1/2 and rapamycin suppressed the increase.Conclusions: The development of postischemic seizure in diabetic animals is associated with activation of mTOR and ERK1/2 pathways. Rapamycin treatment inhibited the postischemic seizure and suppressed the mTOR and ERK1/2 signaling.