Behavioural differences between C57BL/6 and 129S6/SvEv strains are reinforced by environmental enrichment.

Housing in enriched environment has been advocated as a means for controlled variation of environmental conditions in transgenic studies to explore interactions between genes and surroundings. In the present study, behavioural phenotypes of C57Bl/6 (B6) and 129S6/SvEv (129) mice, housed in either standard laboratory conditions or environmentally enriched conditions, were explored. Housing in enriched conditions increased exploratory activity in the plus-maze and reduced habituation in the locomotor activity test in B6 mice, whereas in 129 mice increased hot plate latencies and reduced aggression were observed. Compared to B6, 129 strain displayed lower exploratory activity in the plus-maze and locomotor activity test, longer hot plate latencies, spent more time immobile in the forced swim test and engaged more in social interaction. These behavioural differences between the two strains were reproducible independent of pre-experimental housing conditions. Moreover, environmental enrichment accentuated dissimilarities between the strains in the plus-maze, locomotor activity, hot plate and forced swim test. By contrast, strain differences in anxiety-like behaviours in the plus-maze test and in aggressive encounters in the resident-intruder test were not reproducible in mice housed in alternative environmental conditions, suggesting a strong contribution of environmental factors to the development of these phenotypes. It is concluded that the application of environmental enrichment in addition to standard housing conditions is a meaningful approach for testing reproducibility of behavioural findings within one laboratory.