Influence of age on reactivity to diverse emotional challenges in low- and high-anxiety rats

Studies have revealed that the extent of reactivity of high-anxiety rats to diverse challenges is different than low-anxiety rats and have provided important insights into the psychopathology of anxiety. Various factors intervene to allow defensive mechanisms to react to diverse threatening challenges, including ontogeny and the nature of the emotional challenge (e.g., conditioned vs. unconditioned). The present study investigated the extent to which a particular type of fear extrapolates to other emotional responses to diverse threatening challenges. Groups of 30- and 60-day-old rats were assigned to low freezing behavior (LFB) and high freezing behavior (HFB) groups using the contextual fear conditioning paradigm and subjected to either the fear-potentiated startle (FPS) test, novelty-induced ultrasound vocalizations (USVs) or elevated plus-maze (EPM) tests. At 30 days of age, HFB rats exhibited greater FPS than LFB rats. In contrast, prior selection of HFB and LFB did not affect the performance of 30-day-old animals in the EPM and novelty-induced USVs. Sixty-day-old animals exhibited a performance deficit in all three tests. These data suggest that the performance of young rats in animal models of anxiety parallels their selection as LFB and HFB in the contextual fear conditioning paradigm. However, the increased fear-like behavior exhibited by the 60-day-old HFB rats may elicit performance deficits in conditioned and unconditioned fear tests. These results suggest that the interaction between hyperanxiety and age may cause a performance deficit despite the animals' increased fear-like behavior when facing emotional challenges, thus resembling psychiatric patients in many respects.