Although the relationship between stress intensity and memory function is generally believed to follow an inverted-U-shaped curve, strikingly this phenomenon has not been demonstrated under the same experimental conditions. We investigated this phenomenon for rats' performance in a hippocampus-dependent learning task, the radial arm water maze (RAWM). Variations in stress intensity were induced using different water temperatures (258C, 198C, and 168C), which elicited increased plasma corticosterone levels. During spatial training over three consecutive days, an inverted-U shape was found, with animals trained at 198C making fewer errors than animals trained at either higher (168C) or lower (258C) stress conditions. Interestingly, this function was already observed by the last trial of day 1 and maintained on the first day trial of day 2. A long-term recall probe test administered under equal temperature conditions (208C) revealed differences in performance according to the animals' former training conditions; i.e., platform searching for rats trained at 258C was less accurate than for rats trained at either 168C or 198C. In reversal learning, groups trained at both 198C and 258C showed better performance than the 168C group. We also found an interaction between anxiety and exploration traits on how individuals were affected by stressors during spatial learning. In summary, our findings confirm, for the first time, the existence of an inverted-U-shape memory function according to stressor intensity during the early learning and memory phases in a hippocampus-dependent task, and indicate the existence of individual differences related to personality-like profiles for performance at either high or low stress conditions.[Supplemental material is available online at http://www.learnmem.org.]Physiological stress responses are used by organisms to adapt to changing, demanding circumstances, so these responses are of enormous adaptive value (Lightman 2008). However, survival success depends not only on the immediate ability to respond to threat, but also on the integration of previously acquired knowledge and skills into effective strategies to facilitate coping with similar demands in the future. This view provides an evolutionary explanation for stress effects on learning and memory processes.Understanding the nature of stress-memory interactions has attracted significant attention in recent years. Surprisingly, despite much investigation, it is still not known how stress severity affects memory function. It is generally believed that the relationship between stress intensity and memory function follows an inverted-U-shaped curve, with memory increasing with stress to an optimal point, above or below which memory decreases. However, this stress-memory relationship seems to not apply to classical (Pavlovian) conditioning processes (for review, see Sandi and Pinelo-Nava 2007). Rather, current evidence supports a linear relationship between stressor intensity and the strength of the fear-conditioned memory formed, with a...

Intimate partner violence is a ubiquitous and devastating phenomenon for which effective interventions and a clear etiological understanding are still lacking. A major risk factor for violence perpetration is childhood exposure to violence, prompting the proposal that social learning is a major contributor to the transgenerational transmission of violence. Using an animal model devoid of human cultural factors, we showed that male rats became highly aggressive against their female partners as adults after exposure to non-social stressful experiences in their youth. Their offspring also showed increased aggression toward females in the absence of postnatal father–offspring interaction or any other exposure to violence. Both the females that cohabited with the stressed males and those that cohabited with their male offspring showed behavioral (including anxiety- and depression-like behaviors), physiological (decreased body weight and basal corticosterone levels) and neurobiological symptoms (increased activity in dorsal raphe serotonergic neurons in response to an unfamiliar male) resembling the alterations described in abused and depressed women. With the caution required when translating animal work to humans, our findings extend current psychosocial explanations of the transgenerational transmission of intimate partner violence by strongly suggesting an important role for biological factors.

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