Higher susceptibility to 6Hz corneal kindling and lower responsiveness to antiseizure drugs in mouse models of Alzheimer's disease.

Abstract

Epileptic spikes and seizures seem present early in the disease process of Alzheimer's disease (AD). However, it is unclear how soluble and insoluble amyloid beta (Aβ) and tau proteins affect seizure development in vivo. We aim to contribute to this field by assessing the vulnerability to 6Hz corneal kindling of young female mice from two well-characterized transgenic AD models and by testing their responsiveness to selected antiseizure drugs (ASDs). We used 7-week-old triple transgenic (3xTg) mice that have both amyloid and tau mutations, and amyloid precursor protein Swedish/presenillin 1 dE9 (APP/PS1) mice, bearing only amyloid-related mutations. We assessed the absence of plaques via immunohistochemistry and analyzed the concentrations of both soluble and insoluble forms of Aβ1-42 and total tau (t-tau) in brain hippocampal and prefrontal cortical tissue. Seven-week-old mice of the different genotypes were subjected to the 6Hz corneal kindling model. After kindling acquisition, we tested the anticonvulsant effects of three marketed ASDs (levetiracetam, brivaracetam, and lamotrigine) in fully kindled mice. No Aβ plaques were present in either genotype. Soluble Aβ1-42 levels were increased in both AD genotypes, whereas insoluble Aβ1-42 concentrations were only elevated in APP/PS1 mice compared with their respective controls. Soluble and insoluble forms of t-tau were increased in 3xTg mice only. 3xTg and APP/PS1 mice displayed more severe seizures induced by 6Hz corneal kindling from the first stimulation onward and were more rapidly kindled compared with control mice. In fully kindled AD mice, ASDs had less-pronounced anticonvulsive effects compared with controls. Mutations increasing Aβ only or both Aβ and tau in the brain enhance susceptibility for seizures and kindling in mice. The effect of ASDs on seizures measured by the Racine scale is less pronounced in both investigated AD models and suggests that seizures of young AD mice are more difficult to treat.