NMDA Receptor Composition Differs Among Anatomically Diverse Malformations of Cortical Development

Abstract

Altered excitatory synaptic activity is likely a key factor in the neuronal hyperexcitability of developmental cerebral malformations. Using a combined morphologic and molecular approach, we investigated the NMDA receptor and related protein composition in human epileptic patients affected by periventricular nodular heterotopia, subcortical band heterotopia, or focal cortical dysplasia. Our results indicate that expression levels of specific NMDA receptor subunits are altered in both cerebral heterotopia and cortical dysplasia. A selective increase in the NR2B subunit was present in all cortical dysplasia, whereas the expression level of NR2A and NR2B subunits was significantly downregulated in all patients with heterotopia. NR2B upregulation in cortical dysplasia was greater in the total homogenate than the postsynaptic membrane fraction, suggesting that mechanisms other than increased ionic influx through the postsynaptic membrane may sustain hyperexcitability in dysplastic neurons. In cerebral heterotopia, the NR2A and NR2B downregulation was accompanied by less evident reduction of the SAP97 and PSD-95 proteins of the MAGUK family, thus suggesting that NMDA impairment was associated with altered molecular structure of the postsynaptic membrane. Our results demonstrate that diverse human developmental malformations are associated with different alterations of the NMDA receptor, which may contribute to the genesis of epileptic phenomena.

Seizures, enhanced excitation, and increased vesicle number in Lis1 mutant mice

“…Given that electrophysiological analysis of inhibitory synapses in these same animals, 15 including paired-pulse stimulation experiments, failed to reveal similar deficits we also believe these findings are specific to excitatory glutamatemediated synaptic transmission. Our findings are in contrast to studies in rodent malformation models 13,14,16 and human epileptic patients with heterotopia or focal cortical dysplasia 12,27,28 in which alterations in postsynaptic NMDA-type glutamate receptor subunit expression or function were reported. However, in a rodent model of polymicrogyria 20,29 and both the kainate and pilocarpine models of TLE, 18,19,30 a similar increase in EPSC frequency was observed, suggesting that enhanced excitatory drive may be a common feature of the epileptic brain.…”

Growth‐associated protein 43 and progressive epilepsy in cortical dysplasia

“…Second, the increase in GAP-43 proteins could be modulated by NMDA receptor activation 34,35. Previous studies have demonstrated upregulation of the NMDA receptor complex in dysplastic neurons 23,27,28,36–38. Such hypothesis can be tested by immunostaining for both GAP-43 and NMDA receptors and the protein levels for both in relation to epilepsy duration in larger patient sample.…”

Continuous neurodegeneration and death pathway activation in neurons and glia in an experimental model of severe chronic epilepsy

“…and GFAP, Molecular Probes; 1:2,000) or Alexa Fluor 488 GAM (for cytochrome-c, Molecular Probes; 1:2,000) were incubated with 10% normal goat serum and Triton 0.3% in PBS for 60 minutes and then overnight at 4°C with either the anti-cleaved caspase-3 or the anti phospho-c-Jun primary antibodies. The sections were then incubated for 2 hours with Alexa Fluor 488 or 546 GAR (Molecular Probes; diluted 1:2,000), repeatedly rinsed, and mounted as previously described (Finardi et al, 2006). For FJ/GFAP/caspase-3 triple labeling, sections were first immunoreacted with GFAP as previously described.…”