Transgenic Alzheimer mice in a semi-naturalistic environment: more plaques, yet not compromised in daily life.

The behaviour of transgenic animals modelling human diseases such as Alzheimer's disease (AD) is typically characterised in artificial apparatuses rather than labour-intensively observing their spontaneous behaviour in the home environment. Here we report on an in-depth behavioural characterisation of the day-to-day life of a murine model for AD living in a large (6.6 m(2)) semi-naturalistic indoor enclosure. In a genotype-blind investigation, 40 different behavioural patterns of wildtype and transgenic animals were recorded at early ages, before plaques can be found in the brains of the transgenic mice; and later in life, when these mice are known to exhibit AD-like plaques. Basal stress hormone levels (corticosterone) and cerebral amyloid-beta depositions were determined, and compared with individually and group-housed mice from non-enriched standard cages. Semi-naturalistically housed transgenics could not be differentiated from wildtypes by their behavioural profiles nor by basal levels of corticosterone. Surprisingly, the brains of these transgenics revealed an even more pronounced plaque load than controls from standard-housing conditions. Behavioural traits are known to involve gene-environment interactions. Here we show for the first time that despite high beta-amyloid plaque load the day-to-day life of AD mice is not compromised when the genetic predisposition interacts with a generous physically and socially enriched environment.