Abstracts

Rationale: Mammalian Target of Rapamycin (mTOR) pathway is activated following trauma and during epileptogenesis, and inhibition of mTOR can reduce axonal sprouting and the number of seizures in some acquired epilepsy models. Binding of insulin and Insulin-like Growth Factor 1 (IGF-1) to their respective receptors in neurons can activate mTOR signaling through PI3K-Akt pathway in cortical impact model of brain trauma. We investigated whether insulin and IGF-1 play a role in epileptogenesis in the organotypic hippocampal culture model of post-traumatic epilepsy. Methods: Organotypic cultures were maintained in six-well plates on a rocking platform in a 37 °C, 5% CO2 incubator for four weeks. We maintained neurons in Neurobasal-A culture medium supplemented with bovine serum albumin (BSA), selenium, and varying concentrations of insulin or IGF-1. We also conducted experiments in Neurobasal-A supplemented with standard commercial culture supplement B27, with addition of different concentrations of picropodophyllotoxin (PPP), an IGF-1 receptor inhibitor. We quantified electrographic seizure activity with recordings of field potentials in CA1 and with measurements of lactate concentration in the used culture medium. Neuronal death was quantified by Nissl-staining and surviving neuron counts, and measurements of LDH release into culture medium. Results: We found that addition of insulin or IGF-1 to culture medium was neuroprotective immediately following injury, DIV 0 - 3, but caused increased spontaneous electrographic seizures and cell death between DIV 7 and DIV 28. We also found that chronic application of PPP reduced ictal-like activity and cell death between DIV 7-28. Conclusions: Insulin and IGF-1 are neuroprotective immediately following trauma, but promote epileptogenesis in the long term. Therapy design for head trauma patients should take differential action of these hormones into account - early treatment may need to focus on neuroprotection, while later treatment can emphasize inhibition of epileptogenesis.