Hippocampal cytotoxic lesion effects on species-typical behaviours in mice

The behavioural effects of hippocampal lesions have been extensively documented in rats. However, paradigms developed for rats cannot be assumed to transfer straightforwardly to mice; the behaviour of the two species differs in many respects. Mice are currently the species of choice for targeted genetic manipulations. A number of these programs aim to modulate hippocampal function. The present studies were therefore designed to provide a behavioural profile of selective, cytotoxic hippocampal lesions in tasks appropriate for mice. The lesions abolished food hoarding from a source outside the home base, and reduced the tendency to displace food pellets from a tube inside the home cage (burrowing). Lesioned mice showed reductions of directed exploration (rearing and head dipping), but not locomotor activity, in a holeboard and open field, and explored the edges of their home cages less when the lids were removed. Nest construction was also impaired. These effects were not due to gross motor impairments, as formal tests revealed no deficiencies in co-ordination or strength. There were suggestions of changes in emotionality, although a more consistent finding was that lesioned mice were often slower to initiate behaviour in novel surroundings, which may be congruent with the other deficits we observed. These results may aid interpretation of the many genetic manipulations that target the hippocampus, and of neurodegenerative conditions that induce hippocampal pathology.