Spatial processing and emotionality in aged NMRI mice: a multivariate analysis

The goal of this study was to investigate possible relationships between different aspects of behavioural decline in aged (17 months) NMRI mice by a multivariate analysis. These mice presented defects in spatial processing both in place learning in a Morris-type water maze and in spontaneous alternation in a Y-maze, as well as showing changes in their behaviour in the elevated plus maze test of fear/anxiety and open-field ambulation. Data were first factor analysed and then correlated on the basis of variable factor scores. The results showed clearly that age-related behavioural changes were independent of each other except between open-field activity measured over 6 min and spatial learning indices in the Morris-type water maze, in that mice performing poorly in the latter were more active in the open field, and between the ratio open/total arms visited in the elevated plus maze task and locomotor activity during the first 2 min of the open-field test. It is proposed that the notion of an allocentric or locale system cannot be applied unitarily to both spatial learning and spontaneous alternation defects, and that activity levels in the aged mice are task dependent and reflect different underlying factors.