Benzodiazepine anti-conflict effects in Maudsley reactive (MR/Har) and non-reactive (MNRA/Har) rats

The Maudsley Reactive (MR/Har) and Non-Reactive (MNRA/Har) rat strains, bred originally by Broadhurst for differences in Open Field Defecation, also differ in their control (i.e., non-drug) behavior in the Conditioned Suppression of Drinking (CSD) conflict procedure, a second "model" behavior for the study of anxiety and/or emotionality in rats. The present studies compared the effects of diazepam and alprazolam on CSD behavior in these two strains of rats. In daily 10-min sessions, water-deprived rats were trained to drink from a tube that was occasionally electrified (0.2-0.5 mA), electrification being signaled by a tone. Both diazepam and alprazolam increased punished responding in a dose-related manner. The per cent increase in punished responding (for diazepam only) was comparable in the two strains; however, both statistical and empirical approaches indicated that the magnitude of the anti-conflict effect of benzodiazepines in MNRA/Har versus MR/Har rats was not related to differences in baseline (i.e., non-drug) punished responding. Based on the absolute change in shocks received, rats of the MNRA/Har strain exhibited a significantly greater anti-conflict effect following diazepam or alprazolam treatment than did rats of the MR/Har strain. These findings further the hypothesis that the behavioral differences exhibited by Maudsley MR/Har and MNRA/Har rat strains may constitute a genetically-based "animal model" for the study of emotionality and/or anxiety.