Absence of neurogenic response following robust predator-induced stress response.

Traumatic events contribute to a variety of neuropsychiatric disorders including post-traumatic stress disorder (PTSD). Identifying the neural mechanisms that affect the stress response may improve treatment for stress-related disorders. Neurogenesis, the production of neurons, occurs within the adult brain and disturbances in neurogenesis in the subgranular zone (SGZ) of the hippocampus have been linked to mood and anxiety disorders. Chronic stress models have mainly suggested correlations with stress reducing adult SGZ neurogenesis, whereas acute stress models and those with a naturalistic component that are also associated with long-lasting behavioral changes have produced inconsistent results. Therefore, the goal of the current study was to examine the effects of acute predator stress on adult neurogenesis. Predator stress involved a single 10-min unprotected rat to cat exposure that has previously been shown to produce contextual fear, hyperarousal, and anxiety-like behavior lasting at least 3weeks. As expected, predator stress produced a stress response as detected by elevated corticosterone (CORT) levels immediately after stress. Despite this robust stress response, there was no significant difference between stressed and handled control rats in the number of proliferating or surviving cells as assessed by a 5-bromo-2'-deoxyuridine-immunoreactive (BrdU-IR) labeling 2h or 4weeks post-stress throughout the rostro-caudal axis of the SGZ, respectively. Additionally, 90% of 4-week-old BrdU-IR cells in both conditions expressed NeuN, suggesting no change in cell fate with stress exposure. Overall, these data give caution to the notion that acute predator stress can alter the production or survival of adult-generated cells.

Long-lasting, selective, anxiogenic effects of feline predator stress in mice.

Lasting increases in anxiety-like behavior (ALB) are produced by brief exposure of rats to a cat [Adamec RE, Shallow T, Lasting effects on rodent anxiety of a single exposure to a cat, Physiol. Behav., 54 (1993) 101-109.]. Mice also respond defensively to natural predator stimuli. Moreover, chronic exposure of mice to rat odor has immediate anxiogenic effects in plus maze and lasting (7 days) and effects on acoustic startle. The present study examined the lasting (7 days) after effects on ALB of a brief unprotected exposure of male CFW mice to a cat. Lasting effects on ALB of exposure to the cat exposure room were also assessed. Effects on behavior were studied in the hole board and elevated plus-maze (EPM). An ethological analysis of behavior revealed that risk assessment in the EPM was increased the most in predator-stressed mice. Mice exposed to the cat exposure room showed increased risk assessment falling between controls and cat exposed mice. Behavior in the hole board was unaffected, as were most other behaviors in the plus maze. Factor analysis revealed independence of risk assessment from other measures of ALB, activity and exploration, consistent with findings in rats. Aspects of the stress experience were highly predictive of later response to the cat. Cat biting and pawing, mouse fleeing and mouse weight measured at the time of cat exposure together accounted for 71% of the variance of risk assessment in cat exposed mice. The significance of these findings for vulnerability to cat predator stress of mice and for the use of predator stress in mice as a model of aspects of posttraumatic stress disorder (PTSD) are discussed.