CDKL5 controls postsynaptic localization of GluN2B-containing NMDA receptors in the hippocampus and regulates seizure susceptibility.

Mutations in the Cyclin-dependent kinase-like 5 (CDKL5) gene cause severe neurodevelopmental disorders accompanied by intractable epilepsies, i.e. West syndrome or atypical Rett syndrome. Here we report generation of the Cdkl5 knockout mouse and show that CDKL5 controls postsynaptic localization of GluN2B-containing N-methyl-d-aspartate (NMDA) receptors in the hippocampus and regulates seizure susceptibility. Cdkl5 -/Y mice showed normal sensitivity to kainic acid; however, they displayed significant hyperexcitability to NMDA. In concordance with this result, electrophysiological analysis in the hippocampal CA1 region disclosed an increased ratio of NMDA/α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-mediated excitatory postsynaptic currents (EPSCs) and a significantly larger decay time constant of NMDA receptor-mediated EPSCs (NMDA-EPSCs) as well as a stronger inhibition of the NMDA-EPSCs by the GluN2B-selective antagonist ifenprodil in Cdkl5 -/Y mice. Subcellular fractionation of the hippocampus from Cdkl5 -/Y mice revealed a significant increase of GluN2B and SAP102 in the PSD (postsynaptic density)-1T fraction, without changes in the S1 (post-nuclear) fraction or mRNA transcripts, indicating an intracellular distribution shift of these proteins to the PSD. Immunoelectron microscopic analysis of the hippocampal CA1 region further confirmed postsynaptic overaccumulation of GluN2B and SAP102 in Cdkl5 -/Y mice. Furthermore, ifenprodil abrogated the NMDA-induced hyperexcitability in Cdkl5 -/Y mice, suggesting that upregulation of GluN2B accounts for the enhanced seizure susceptibility. These data indicate that CDKL5 plays an important role in controlling postsynaptic localization of the GluN2B-SAP102 complex in the hippocampus and thereby regulates seizure susceptibility, and that aberrant NMDA receptor-mediated synaptic transmission underlies the pathological mechanisms of the CDKL5 loss-of-function.

[Case of an elderly woman with dementia showing episodic involuntary movement of the tongue].

We report a 93-year-old woman with dementia who developed generalized convulsion and involuntary movement of her tongue. She could independently walk and eat meals until 8 months ago, however she turned into bedridden. When she was admitted to our emergency room due to status epilepticus, her tongue intermittently moved from the midline to the left. She could not eat or speak during this episodic tongue movement. MR imaging study revealed brain atrophy in the bilateral mesial temporal lobe, consistent with senile dementia of Alzheimer type. Despite her tongue movements seemingly developing to the generalized convulsion, EEG study did not indicate epileptiform discharges corresponding to this movement. Although antiepileptic drug therapy was effective, we needed polytherapy to control this movement. Paroxysmal tongue movements were previously reported in cases of epilepsy, brain tumor, and stroke, observed bilaterally in most cases. This episodic tongue movement would be rare in terms of the clear laterality. The etiology of this movement was presumed as focal seizure, palatal tremor, dyskinesia or others, but was undetermined. Episodic movements involving tongue decrease the quality of daily life especially in the elderly. Therefore, we should pay more attention to it and try to treat it earlier.