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

Rationale: A number of previous studies have reported that the Maudsley rea ctive (MR/Har) and nonreactive (MNRA/Har) strains of rats show behavioural and physiological differences consistent with the hypothesis that these str ains differ in emotionality and could therefore be considered a model of tr ait anxiety in humans. Objectives: We sought to confirm this observation by determining their behaviour in various animal models of conditioned and un conditioned fear. Methods: Both strains were evaluated in the open field (O F), conditioned avoidance (CA), elevated plus maze (EPM) and fear-potentiat ed startle (FPS) tests. In the OF the behaviour of both strains was consist ent with previous results showing that reactive rats had significantly high er levels of defecation and lower levels of activity than the nonreactive r ats. 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 ben zodiazepine receptor agonist, chlordiazepoxide, induced quantitatively simi lar effects in both strains of rats. In the FPS test, MNRA/Hars had a highe r baseline level of startle and fear potentiation than the MR/Har rats Conc lusions: 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.