Acute exposure to predator odor elicits a robust increase in corticosterone and a decrease in activity without altering proliferation in the adult rat hippocampus

Abstract

Stress has long been implicated as a major cause of depression in humans and more recently has been suggested to decrease neurogenesis, which may be a contributing factor to depression development. Animal models of stress may be a relevant tool for investigating links between neurogenesis and depression. This has largely been investigated using chronic stress models in rodents. However, stress may be chronic or experienced in discrete episodes. Acute stress may be particularly relevant to humans experiencing unexpected societal pressures and obligations. Our study examined the effect of acute stress on the proliferative phase of adult hippocampal neurogenesis. Young adult rats were exposed for 20 min to the predator odor TMT, a natural stressor for rodents with significant ethological relevance. BrdU IP injections were concurrent with TMT exposure to assess proliferation effects with animal sacrifice 2 h after BrdU injection. Robust stress responses were evident following TMT exposure as detected by elevated corticosterone (CORT) levels and a significant reduction in exploratory behavior. Exposure to TMT did not alter the number of BrdU-positive cells in the hippocampus despite physiological and behavioral evidence of stress. CORT level elevation has long been accepted as a marker of stress; however, this study indicates that increases in CORT level may not always correlate with diminished neurogenic proliferation. This study further suggests that various stressors may not operate through the same biological substrates resulting in a differential ability to modulate neurogenesis.