Individual differences in fear-related reactivity in transgenic mice carrying APP and PS1 mutation - random variable, hearing impairment or a personality trait?

H. Iivonen, E. Koivisto and H. Tanila

Department of Neuroscience and Neurology, University of Kuopio, Kuopio, Finland.

Alzheimer’s disease is associated with a variety of behavioral symptoms in addition to cognitive impairment, and these behavioral symptoms are usually the primary cause for institutionalization of the patients. We have used transgenic mice carrying mutated human amyloid precursor protein (APP) and presenilin-1 (PS-1) genes as a model for the disease. These animals develop amyloid plaques from 5-months of age on and show progressive impairment in their spatial learning ability. We used acoustic startle and prepulse inhibition as a measure to the innate reactivity of these mice in comparison to their negative littermates. We tested these animals at 4 and 12 months of age, and expected the reactivity to dramatically attenuate with age, as these animals had C57BL/6J background with reported age-associated hearing loss. Unexpectedly, we came across a huge individual variability in the startle responses in both genotypes and age groups. In order to clarify the reason for the individual differences we further studied acoustic startle response using different sound pressure levels for the pre-pulse and the main pulse. Furthermore, we are currently testing the animals in other fear-related behaviors, the elevated plus maze and novelty suppressed feeding. The results will help the interpretation of acoustic startle responses in genetically manipulated animals with C57B6 background.

Paper presented at Measuring Behavior 2005 , 5^th International Conference on Methods and Techniques in Behavioral Research, 30 August - 2 September 2005, Wageningen, The Netherlands.

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