A comparison between Dark Agouti and Sprague-Dawley rats in their behaviour on the elevated plus-maze, open-field apparatus and activity meters, and their response to diazepam

Rationale: Preliminary unpublished studies in our laboratory suggested that the behaviour of Sprague-Dawley (SD) and Dark Agouti (DA) rats was markedly different, on both the elevated plus maze and in the open-field apparatus. We wished to confirm and extend this initial finding. Objective: The study was designed to examine the behaviour of SD and DA rats in the elevated plus maze, open-field apparatus and automated, activity meters. The response of both strains on the elevated plus maze following diazepam (1 mg/kg and 1.5 mg/kg) administration was subsequently investigated. Results: DA rats showed markedly greater anxiety-like behaviour than SD rats in both the plus maze and open field, with fewer percentage open/total arm entries and percentage time spent on open/total arms in the plus maze and fewer crossings in the open field. Acute handling plus administration of vehicle abolished this difference in anxiety levels, with DA rats showing similar open-arm behaviour to that of SD rats. Both strains demonstrated a clear anxiolytic response, to diazepam (1 mg/kg) in terms of percentage time spent on the open arms, but only SD rats had a statistically significant increase in percentage open-arm entries compared with vehicle-injected control animals. Conclusions: While the high level of anxiety-like behaviour of DA rats versus SD rats could prove useful in future ethological studies on anxiety, the fact that acute handling decreased the anxiety-like behaviour on the elevated plus maze may limit the value of this strain for the study of putative anxiolytic drugs.