Explorations of coping strategies, learned persistence, and resilience in Long-Evans rats: innate versus acquired characteristics.

In the current investigation, predispositions for coping styles (i.e., passive, flexible, and active) were determined in juvenile male rats. In subsequent behavioral tests, flexible copers exhibited more active responses. In another study, animals were exposed to chronic stress and flexible coping rats had lower levels of corticosteroids. Focusing on the acquired nature of coping strategies, rats receiving extensive training in a task requiring them to dig for food rewards (i.e., effort-based rewards) persisted longer in a challenging task than control animals. Thus, the results suggest that both predisposed coping strategies and acquired behavioral experience contribute to resilience in challenging situations.

Maternal experience produces long-lasting behavioral modifications in the rat.

From 5 to 22 months of age, cognitive and emotional responses of nulliparous, primiparous, and multiparous rats were assessed using a dry land maze (DLM) and an elevated plus-maze (EPM) at 4-month intervals. Parous rats exhibited improved spatial memory in the probe and competitive versions of the DLM, and more exploration in the EPM and a novel stimulus test relative to nulliparous females. The nulliparous females, however, outperformed parous rats during the DLM visual cue test at 17 months of age. At 23 months, no differences in stressed corticosterone levels or Golgi-stained hippocampal neurons were observed. Thus, cognitive and emotional modifications were observed in parous rats; the neurobiological mechanisms for these enduring effects, however, remain to be identified.

Pup exposure differentially enhances foraging ability in primiparous and nulliparous rats.

The role of maternal experience (i.e., pregnancy and pup exposure) on rats' performance in a foraging task was assessed. Primiparous (P) and nulliparous (N) animals were either exposed to pups for 21 days (+) or received no pup exposure (-). Following habituation trials, all animals were tested in spatial and cued versions of the dry land maze (DLM) for three days (three trials per day). In the spatial DLM, the presence of pups decreased latencies in both N and P groups in Trial 5 and P+ rats exhibited shorter latencies to baited food wells than P- animals on Trial 6. In the subsequent probe trial, P+ animals spent significantly more time in proximity to the previously baited well than P- rats. Pups enhanced performance of both P+ and N+ groups in trial 6 of the cued test. Thus, in the spatial task, the individual components of the maternal experience (e.g., pregnancy, parturition, lactation, and pup exposure) converge to produce behavioral modifications in the DLM spatial and probe tasks that enable the female to care for her offspring, in this case, by enhancing foraging behavior. Further, in one trial of each version of the task, pup exposure enhanced performance in N animals suggesting that, in isolation, pup exposure may be a more important influence on ancillary maternal behavior than the pregnancy itself.