A seizure is one of the leading neurological disorders. NMDA receptor-mediated neuronal excitation has been thought to be essential for epileptogenesis. As an endogenous co-agonist of the NMDA receptor, D-serine has been suggested to play a role in epileptogenesis. However, the underlying mechanisms remain unclear. In the current study, we investigated the effects of antagonizing two key enzymes in D-serine metabolism on the development of seizures and the downstream signaling. Our results showed that serine racemase (SR), a key enzyme in regulating the L-to-D-serine conversion, was significantly up-regulated in hippocampal astrocytes in rats and patients who experienced seizure, in comparison with control rats and patients. L-aspartic acid β-hydroxamate (LaaβH), an inhibitor of SR, significantly prolonged the latencies of seizures, shortened the durations of seizures, and decreased the total EEG power in rats. In contrast, D-amino acid oxidase inhibitor 5-chlorobenzo[d]isoxazol-3-ol (CBIO), which can increase D-serine levels, showed the opposite effects. Furthermore, our data showed that LaaβH and CBIO significantly affected the phosphorylation of Extracellular Signal-regulated Kinase (ERK). Antagonizing or activating ERK could significantly block the effects of LaaβH/CBIO on the occurrence of seizures. In summary, our study revealed that D-serine is involved in the development of epileptic seizures, partially through ERK signaling, indicating that the metabolism of D-serine may be targeted for the treatment of epilepsy.

Aims. To determine the electroclinical features of fixation‐off sensitivity (FOS) in patients with idiopathic generalized epilepsy (IGE). Methods. We searched the EEG database using the terms “fixation‐off sensitivity” and “idiopathic generalized epilepsy” over a four‐year period from March 2014 to April 2018 in the Xijing Hospital, Xi’an, China. FOS was evaluated according to the technique proposed by Panayiotopoulos. Photic stimulation procedure and neuropsychological testing were performed during video‐EEG monitoring. Results. FOS was observed in eight patients with several different IGE syndromes, including four with eyelid myoclonia/Jeavons syndrome, two with juvenile myoclonic epilepsy, one with photosensitivity epilepsy, and one with epilepsy with generalized tonic‐clonic seizures only. FOS was associated with seizures in five patients manifesting with eyelid myoclonic, myoclonic, and myoclonic‐tonic‐clonic seizures, and eyelid myoclonic status. FOS coexisted with photosensitivity in six patients as independent EEG features. Neuropsychological testing revealed transitory cognitive impairments associated with FOS. Conclusions. FOS is associated with several different IGE syndromes and may coexist with photosensitivity in the same patient as independent EEG features. FOS may be associated with both clinical seizures and cognitive impairments. Intermittent photic stimulation and registration of different eye conditions with and without fixation will aid the study of the dynamics of the visual system in epilepsy patients. [Published with video sequences on http://www.epilepticdisorders.com]

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