Abstracts

Rationale: Whether epilepsy could be considered a progressive disorder is a long-debated issue. To investigate possible effects of severe epilepsy on the malformed brain and the cellular and molecular basis of epileptogenicity, we performed a parallel analysis of surgical samples from type IIB focal cortical displasia (FCD) patients and a rat model of acquired FCD (methyl-axozymethanol [MAM]/pilocarpine rats: MP rats; Colciaghi et al, 2011Brian:134:2828-43).Methods: We analyzed epileptogenic/dysplastic areas from surgical samples from type IIB FCD patients (n=8), adjacent areas (with no overt cytological abnormalities) from the same patients, as internal controls, and samples from non-dysplastic controls (n=9). We also analyzed epileptic MP rats at different time points: 3-5 days (early-chronic, MP-EC: n=8), 3 months (MP-3m: n=17) and 6 months (MP-6m: n=9) after epilepsy onset. As controls, we used MAM rats receiving diazepam (DZP) before pilocarpine, not experiencing either SE or spontaneous seizures (MDP rats). In both human and rats samples, we carried out a morphologic/morphometric analysis of dysplastic neurons, investigated the glutamatergic synaptic input and the expression of N-methyl-D-aspartate (NMDA) receptor subunits and associated membrane-associated guanylate kinase (MAGUK).Results: Our findings indicated that the dysplastic areas giving rise to epileptic discharges of all FCDIIB patients were characterized by i) largest dysmorphic neurons and ii) increased glutamatergic inputs compared to adjacent areas with normal cytology (***p<0.001). In addition, the duration of epilepsy was found to correlate with largest dysmorphic neuron size (Pearson s r=0.94, **p<0.01). Consistent with the increased glutamatergic input, western blot revealed that NMDA regulatory subunits and related MAGUK proteins were up-regulated in epileptogenic/dysplastic areas of all FCD patients. Neuronal soma size of cortical pyramidal neurons was also significantly increased in MP-3m and MP-6m when compared to MDP and MP-EC rats (**p<0.01), associated with significant reduction of average total dendrite length and spine density (*p<0.05 and **p<0.01, respectively). We also found an imbalance between excitatory and inhibitory input in both neocortex and hippocampus of MP vs MDP rats, with clear preponderance of glutamatergic synapses. At the post-synaptic level, a persistent hyper-activation of the NR2B subunit was found in epileptic MP versus non-epileptic MDP brains at different time-points after epilepsy onset. Conclusions: Data from human FCD samples and our rat model indicate in both conditions: i) that SE and/or seizures can further modify the cellular/molecular settings of the malformed epileptic cortex; ii) the predominance of excitation vs inhibition; iii) the dysregulation of the NMDA/MAGUK expression. Taken together, these results support the hypothesis that epilepsy itself, at least in the malformed brain, can alter morphology and possibly function of the epileptic cortex, and suggest that glutamate/NMDA/MAGUK dysregulation might be the underlying intracellular trigger.