Differential effects of repeated fluoxetine and ketamine administration on behavioral and pharmacological stressor-induced depression of digging behavior in mice.

Major depressive disorder is a multifactorial disorder that originates from a complex web of variables and overlaps with similar disorders (e.g., depression and anxiety). As such, animal models should account for the considerable symptom overlap between psychiatric disorders. We sought to extend the findings of behavioral assays that encompass both anxiety and stress/depression components. To do so, we have focused on digging behavior, a compulsive-like behavior displayed in mice, in which we employed behavioral and pharmacological stressors to reduce digging behaviors, producing a depression-like state. Locomotor activity was assessed during each test session. We found that digging behavior remains consistent, but locomotor activity decreased when exposed to multiple test sessions over 4 weeks and no sex differences were observed. A time-course study showed a single swim stress significantly reduced digging behavior for at least 3 days but rebounded to baseline levels by Day 7. Repeated treatment of 10 mg/kg/day fluoxetine, but not ketamine, partially reversed swim stress-induced depression of digging behavior on Days 3 and 7. The pharmacological stressor yohimbine (1.0-5.0 mg/kg) dose-dependently decreased digging behavior. Repeated treatment of 10 mg/kg/day ketamine, but not fluoxetine, reversed yohimbine-induced depression of digging behavior on Days 3 and 7. These data suggest that digging behavior is a stable and consistent behavior displayed by all mice. We were able to depress digging behavior with both behavioral and pharmacological stress. However, the reversal of stress-induced depression of digging behavior was stimulus- (e.g., behavioral vs. pharmacological) and drug-dependent and will require further investigation. (PsycInfo Database Record (c) 2024 APA, all rights reserved).