Abstracts

Rationale: Prolonged, low-frequency (6 Hz) electrical stimulation in mice induces complex partial seizures characterized by a stunned or immobilized posture and rearing, forelimb clonus, and twitching. This seizure model is interesting because it has a distinct profile of pharmacological sensitivity and may identify agents with a broader spectrum of clinical activity than conventional antiepileptic drug screening tests. Since the ketogenic diet has been used clinically in drug-resistant epilepsies, we sought to determine whether it is active in the 6 Hz model.Methods: Starting at 3 weeks of age (i.e., after weaning), male NIH Swiss mice were fed a normal or ketogenic diet (Bioserv F3666, Frenchtown, NJ) ad libitum and were evaluated in the 6 Hz test (stimulus duration 3 sec; pulse width 0.2 msec). Blood glucose and β-hydroxybutyrate levels were measured on the day of seizure testing.Results: The mean CS50 (current intensity producing seizures in 50% of mice tested) values in the 6 Hz test were 50.6 (95% C.L., 46.3–55.3) mA and 15 (95% C.L., 14.0–16.1) mA in mice fed for 12 days with the ketogenic diet and the normal diet, respectively (P < 0.001). The mean CS50 value also was elevated markedly in separate experiments in which the ketogenic diet and normal diet were fed for 16 days, but not for 2, 5 and 21 days. The mean CS50 values of the 5 groups fed the normal diet did not differ significantly, indicating the CS50 value does not vary with age (from 3 to 6 weeks) or weight (ranging from 12 to 24 g) during the rapid growth phase studied here. β-Hydroxybutyrate levels were significantly higher and glucose levels were significantly lower in mice fed the ketogenic diet than in those fed the normal diet. Blood glucose and β-hydroxybutyrate levels did not correlate with the CS50 values.Conclusions: The ketogenic diet strongly elevates the seizure threshold in the 6 Hz test in a time-specific manner, requiring more than 5 days of dietary treatment for seizure protection to be evident. The efficacy of the diet waned at 3 weeks, despite persistently elevated β-hydroxybutyrate and low blood glucose. Therefore, protection from seizures in this model appears to be unrelated to the level of ketosis. Seizure thresholds in mice fed the normal diet were insensitive to body weight and age, demonstrating that the 6 Hz model is appropriate to assess anticonvulsant regimens, including dietary therapies, where animal weight or age may be a confounding factor. The 6 Hz model may be useful in mechanistic studies of the ketogenic diet and also for experiments to determine why the ketogenic diet loses efficacy in some patients.