Gene Dosage Dependent Aggravation of the Neurological Phenotype in the 5XFAD Mouse Model of Alzheimer's Disease.

In the present report, we extend previous findings in the 5XFAD mouse model with regard to a characterization of behavioral deficits and neuropathological alterations. We demonstrate that these mice develop a robust age-dependent motor phenotype and spatial reference memory deficits when bred to homozygosity, leading to a strongly reduced age of onset of behavioral symptoms. At postnatal day sixteen, abundant AβPP was detected in subiculum and cortical pyramidal neurons. From six weeks on, intraneuronal Aβ could be detected which was much more abundant in homozygous mice. The same gene-dosage effect was seen on memory and motor deficits. While at 2 months of age neither heterozygous nor homozygous 5XFAD mice show any neurological phenotype except for alterations in anxiety behavior, at 5 months they were clearly evident. Interestingly, despite abundant motor deficiencies, homozygous 5XFAD mice were able to perform the acquisition training of the Morris water maze task with no difference in the swimming performance between the groups. Therefore the aggravated spatial memory and spatial reference memory deficits of the homozygous mice correlated with the elevated soluble and insoluble Aβ levels. Homozygous 5XFAD mice represent a model with several advantages in comparison to the heterozygous mice, developing amyloid pathology much more rapidly together with a neurological phenotype. These advantages allow reducing the number of animals for Alzheimer's disease research.