Impaired conditioned taste aversion learning in APP transgenic mice.

Cognition in transgenic mouse models of Alzheimer's disease (AD) has been predominantly characterized in explicit spatial orientation tasks. However, dementia in AD encompasses also implicit memory systems. In the present study a line of transgenic mice (TgCRND8) encoding a double mutated allele of the human amyloid precursor protein (APP) genes was evaluated in an implicit associative learning task of conditioned taste aversion (CTA). CTA is a form of Pavlovian classical conditioning, in which a mouse learns to avoid a novel taste of saccharine (conditioned stimulus) paired with an experimentally induced (systemic injection of lithium chloride) nausea (unconditioned stimulus). In contrast to conditioned non-Tg mice, TgCRND8 APP mice developed weaker aversion against saccharine and quickly increased its consumption in repeated tests. These results indicate that TgCRND8 mice show a significant impairment not only in explicit spatial memory, as has been previously shown [Nature 408 (2000) 979], but also in implicit memory. Control experiments confirmed that TgCRND8 and non-Tg mice had comparable taste sensitivities in response to appetitive as well as aversive tastes. The study suggests that the CTA paradigm can be a sensitive tool to evaluate deficits in implicit associative learning in APP transgenic mouse models of AD.