Defensive burying behavior in maudsley reactive (MR/Har) and nonreactive (MNRA/Har) rats

Based upon differences in open field and conflict behaviors, the MR/Har and MNRA/Har rat strains have been proposed as a genetically-based "animal model" for the study of emotionality and/or anxiety. The present study compared the MR/Har and MNRA/Har rat strains in the Defensive Burying paradigm. Prior to testing, female MR/Har and MNRA/Har rats were placed in a 40 X 30 X 40 cm Plexiglas chamber containing clay bedding material (5 cm deep) for 30 minute periods on each of four consecutive days. On the fifth day, a wire wrapped prod was placed at one end of the chamber. Rats were placed in the chamber singly and a 3 mA shock was delivered upon contact with the prod. Defensive Burying behavior (i.e., the moving of bedding material toward or over the prod) was recorded for each animal for 15 minutes postshock. There was no MR/Har versus MNRA/Har difference in the percent of animals exhibiting Defensive Burying, nor was there a MR/Har versus MNRA/Har difference in the latency to initiation or the duration of this behavior. Thus, these genetically-defined Maudsley rat strains do not appear to differ in all "animal models" for the study of anxiety or fear.