Abstracts

Rationale: The mammalian target of rapamycin (mTOR) pathway integrates signals from different metabolites, including amino acids and glucose. mTOR inhibitors decrease seizures in patients and genetically engineered mice with tuberous sclerosis mutations (Zeng et al., 2008; Krueger et al., 2010). Rapamycin, one mTOR inhibitor, decreases seizure frequency in some, but not all, chronic seizure models (Zeng et al., 2009; Ljungberg et al., 2009; Huang et al., 2010; Buckmaster et al., 2011). In contrast, in vitro studies have shown that rapamycin does not have a significant effect on neuronal excitability (Daoud et al., 2007; Ruegg et al., 2007). Thus, in considering potential mechanisms of action, it is unknown whether mTOR inhibitors exert anticonvulsant or antiepileptogenic effects. We investigated rapamycin s anticonvulsant effects using acute seizure tests in normal mice.Methods: Male NIH Swiss mice aged 4-5 weeks were given rapamycin 4.5 mg/kg/day or vehicle intraperitoneally for 3 days (identified in pilot studies as the minimum time and dose required for inhibition of S6 phosphorylation, a measure of mTOR activity; longer treatment periods were associated with significant differences in body weight between groups). Seizure tests included maximal electroshock threshold (MES-T), 6 Hz test (both of which were preceded by corneal topical anesthesia), and kainic acid. Because this was a metabolism-based intervention, blood glucose and ketones were measured prior to seizure testing.Results: Rapamycin protected against tonic hindlimb extension in the MES-T test (P = 0.02). In this test, mice treated with rapamycin also had seizures that were of shorter duration than vehicle-treated mice. In the kainic acid test, mice treated with rapamycin had less severe seizures overall (P < 0.0001), spent less time having convulsive seizures (P = 0.02) and had lower maximum seizure scores (P = 0.049). In the 6 Hz test, rapamycin-treated mice did not have a statistically significantly different CC50 (i.e., current where 50% of mice had a seizure) than those treated with vehicle, nor were there any differences in seizure duration or maximum score. There were no statistically significant differences between groups in glucose or ketone levels. Mice in both groups appeared to have normal activity levels.Conclusions: Rapamycin has anticonvulsant effects in normal mice. Interestingly, its acute seizure test profile differs from that of other metabolism-based therapies, including the ketogenic diet, intermittent fasting, and 2-deoxy-D-glucose. The anticonvulsant effects could not be attributed to differences in blood glucose and ketone levels. These data do not exclude the possibility that rapamycin also may have antiepileptogenic effects.