Abstracts

Rationale: Therapeutic intervention to reduce the frequency and magnitude of epileptic seizures remains a challenging clinical problem, particularly in children and in patients with medically-intractable epilepsy. One treatment option with minimal side effects that is often successful in difficult cases is a high fat, low carbohydrate ketogenic diet. The specific anticonvulsant mechanisms underlying the success of a ketogenic diet are unknown, but several lines of evidence point to an involvement of the cellular energy store ATP and the retaliatory metabolite adenosine, purines that together act to link alterations in metabolism to decreased neuronal excitability. Adenosine is a well known powerful inhibitory modulator in brain areas where seizures are initiated and propagated. Our research might provide insight into key factors associated with anticonvulsant properties of the ketogenic diet and spawn new therapeutic avenues and the development of more effective and/or less restrictive diets.Methods: At weaning matched groups of rats were placed on either a ketogenic diet or a control diet for at least 3 weeks. In a subset of animals we used a head-focused high-energy microwave system to snap-inactivate molecules and quantify levels of ATP, ADP, AMP, adenosine, phosphocreatine and creatine in discrete brain regions using HPLC. To assess functionally the influence of purines on synaptic transmission we performed electrophysiological recordings in hippocampal slices from both groups of animals and measured the influence of both exogenous and endogenous purines. Acute hippocampal slices were cut in ice-cold artificial cerebrospinal fluid bubbled with 95% oxygen/5% carbon dioxide. Field excitatory postsynaptic potentials were evoked and measured in area CA1. Every 30 sec paired pulse stimuli were delivered with an interstimulus interval of 70 msec.Results: We found changes in purines and high energy molecules in discrete brain regions, including increased ATP levels. Electrophysiological recordings from acute hippocampal slices demonstrated changes in paired pulse facilitation and pharmacological responses that were consistent with increased endogenous adenosine levels. We also observed changes in purinergic signalling over a number of hours in hippocampal slices from control versus ketogenic diet animals.Conclusions: Our data suggest that a ketogenic diet increases levels of purines and purine receptor-mediated anticonvulsant effects in forebrain areas known to initiate and propagate seizures. To date, the use of diet-based anticonvulsant therapies is limited by compliance issues, and developing analogous pharmacologic approaches is hampered by an incomplete understanding of mechanisms underlying the success of the diet. Given that improvements in therapeutic strategies to treat epilepsy will require a fundamental understanding of the underlying mechanisms, it is important and necessary to elucidate mechanisms underlying ketogenic diet-induced alterations in purine metabolism and accompanying changes in brain activity. Supported by NS29173, MH065431 and P20 RR17699 from NCRR a component of NIH.