Symposium 9: Ecology, Brain and Behaviour

Methods to score adequately male mouse aggressive behaviour will be shortly summarised. As an example of ethologically-grounded evaluation, twenty feralized male mice (of a strain characterised by large variability in hippocampal mossy fibers projections) were trapped from a colony living in outdoor large enclosure (300 m2) in western Russia. Twenty control male subjects (of the same origin but maintained in laboratory conditions for several generations) were housed in standard laboratory facilities at the university of Moscow. All mice were isolated for 9 days in standard mouse laboratory cages before being exposed to agonistic encounters in a large cage (53 x 23 x 30 cm) with a mixture of sawdust and sand as bedding material. Behaviour of the mice was video-recorded and analysed during 1st, 3rd and 5th of 5 agonistic encounters lasting 10 min. Feralized mice showed shorter latency to the first attack and a generalised increase of the offensive components of agonistic behaviour (attack, chase, display of offensive upright posture). Only half of the feralized mice, however, showed a steady dominant profile throughout the five sessions. A preliminary neuroanatomical analysis showed that mice with larger brain weight had significantly shorter attack latencies. On the other hand, the extent of the infrapyramidal mossy fiber projection was not correlated with initial attack latencies. In those animals (chiefly from the outdoor pens), which did not show a constant behavioral profile, larger IIP-FM were correlated with increasing attack latencies. The intra/infrapyramidal mossy fiber projection (IIP-MF) of mice and rats shows strong genetic variation found to correlate positively with learning abilities in hippocampus-dependent tasks. However, negative correlations were also observed with non-learned tasks, for example with attack latencies in a male intruder paradigm. In order to elucidate the biological significance of the IIP-MF variation, a double strategy has been employed. For one, we have checked a variety of small mammals in western Russia for differences in the IIP-MF projections in order to discover adaptations to particular ecological profiles. In parallel, we have tested short-term natural selection in populations of laboratory mice kept outdoors in NEURAL PLASTICITY