Lack of consistent behavioural effects of Maudsley reactive and non-reactive rats in a number of animal tests of anxiety and activity

Abstract.

Rationale: A number of previous studies have reported that the Maudsley reactive (MR/Har) and non-reactive (MNRA/Har) strains of rats show behavioural and physiological differences consistent with the hypothesis that these strains differ in emotionality and could therefore be considered a model of trait anxiety in humans. Objectives: We sought to confirm this observation by determining their behaviour in various animal models of conditioned and unconditioned fear. Methods: Both strains were evaluated in the open field (OF), conditioned avoidance (CA), elevated plus maze (EPM) and fear-potentiated startle (FPS) tests. In the OF the behaviour of both strains was consistent with previous results showing that reactive rats had significantly higher levels of defecation and lower levels of activity than the non-reactive rats. However, there were no significant strain differences in CA responses or in the time spent on the open arms of the EPM. In addition, the full benzodiazepine receptor agonist, chlordiazepoxide, induced quantitatively similar effects in both strains of rats. In the FPS test, MNRA/Hars had a higher baseline level of startle and fear potentiation than the MR/Har rats Conclusions: These data show that the behaviour of MR/Har and MNRA/Har rats in some models of conditioned and unconditioned fear is inconsistent with that predicted by their behaviour in the OF test, suggesting that they are not a model of trait fear.