Antipanic drug treatments: failure to exhibit anxiolytic-like effects on defensive burying behavior.

Although the Defensive Burying paradigm has been used as a behavioral "model" for the study of anxiety and/or antianxiety agents, the effects of chronic treatment with antidepressant agents (i.e., "antipanic" agents) have not been examined in this paradigm. The present study examined the effects of two antianxiety treatments on this behavior: 1) acute treatment (30-minute pretreatment) with the benzodiazepine anxiolytic chlordiazepoxide and 2) chronic treatment (twice daily for 7-12 weeks) with the antipanic agents imipramine (IMI), desipramine (DMI) or pargyline (PARG). Prior to testing, female Sprague-Dawley 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 individually 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 15 minutes postshock. In a dose-dependent manner, acute treatment with chlordiazepoxide reduced the frequency of occurrence of burying behavior, increased the latency to initiation of burying, and decreased the duration of burying. In contrast, chronic treatment with IMI, DMI, or PARG failed to exhibit anxiolytic-like effects on any measure of Defensive Burying. These data suggest that the Defensive Burying paradigm may not be an "animal model" for the study of panic disorder and potential antipanic agents.