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Rationale: Differences between laboratory rats are particularly important to behavioural pharmacologists, whose studies depend on well-defined, homogenous backgrounds. It is well known that the anxiety-related behaviour may differ among substrains or lines, which might cause different and sometimes contradictory results using the same behavioural procedure or animal test.
More than 15 years ago (more than 45 generations) the animal facility of the Institute of Cytology and Genetics Siberian Branch of the Russian Academy of Sciences, Novosibirsk started breeding Sprague-Dawley (SD) rats obtained from Charles River Sulzfeld, Germany.
Objectives: Arising of a line with potentially different behaviour could be assumed. Therefore, the behaviour of Russian and Charles River SD rats was analyzed in a test battery: Exploratory behaviour was assessed using the open field and the hole board and anxiety-related behaviour using the elevated plus maze (X-maze) reflecting state anxiety and a free exploratory paradigm (FEP) reflecting mainly trait anxiety.
Methods: Russian SD rats and SD rats from Charles River were born and reared in our animal unit in an identical environment. At the age of 50 days the rats were exposed to the X-maze or the hole board and 14 days later to the open field. At the age of 78 days the rats were tested in the FEP.
Results: Although the Russian SD rats displayed a higher level of motor activity in all tests, there was no significant difference in anxiety-related behaviour in the X-maze between Russian SD rats and SD rats obtained directly from Charles River. However, in the FEP Russian SD rats showed a less ‘anxious’ behaviour. More Russian SD rats explored the environment outside the home cage compared to Charles River rats and Russian rats started exploring earlier, indicating a difference between the two lines in trait anxiety. In the hole board the Russian rats were more active in both trials and showed less habituation to the environment compared to Charles River rats. It has taken into account that increased motor activity may also influence the outcome in exploration based tests.
Summary & Conclusion: Since we reared the two lines of rats under identical conditions, differences in behaviour should be due to genetic differences of the lines.
Albeit the long separation of the two lines did not lead to a change in state anxiety-related behaviour, the other behavioural data show that separation from the origin Charles River stock for at least 45 generations might lead to the arising of a line with partly different behaviour. Due to a lack of information about the breeding in Russia we are not sure whether the differences in general activity are caused either by spontaneous mutations which lead to a genetic drift, or by unrecorded outcrossing.
In conclusion, using strains or substrains obtained from different breeders should be used with caution.