Recurrent stress across life may improve cognitive performance in individual rats, suggesting the induction of resilience

Depressive symptoms are often accompanied by cognitive impairments and recurrent depressive episodes are discussed as a potential risk for dementia. Especially, stressful life events are considered a potent risk factor for depression. Here, we induced recurrent stress-induced depressive episodes over the life span of rats, followed by cognitive assessment in the symptom-free period. Rats exposed to stress-induced depressive episodes learned faster than control rats. A high degree of stress-induced depressive-like behavior early in the paradigm was a predictor of improved cognitive performance, suggesting induction of resilience. Subsequently, exposure to lorazepam prior to stress-induced depressive episodes and cognitive testing in a nonaversive environment prevented the positive effect. This indicates a beneficial effect of the stress-associated situation, with the existence of individual coping abilities. Altogether, stress may in some have a beneficial effect, yet for those individuals unable to tackle these aversive events, consecutive unpleasant episodes may lead to worse cognitive performance later in life

Differences in Mouse Maternal Care Behavior – Is There a Genetic Impact of the Glucocorticoid Receptor?

Depressive episodes are frequently preceded by stressful life events. Evidence from genetic association studies suggests a role for the glucocorticoid receptor (GR), an essential element in the regulation of stress responses, in the pathophysiology of the disorder. Since the stress response system is affected by pregnancy and postpartum-associated changes, it has also been implicated in the pathophysiology of postpartum depression. Using a 2×2 factorial design, we investigated whether a heterozygous deletion of GR would influence maternal care behavior in C57BL/6 and Balb/c mice, two inbred strains known to display qualitative differences in this behavior. Behavioral observation was carried out between postnatal days 1 and 7, followed by a pup retrieval test on postnatal days 7 or 8. While previously noted inter-strain differences were confirmed for different manifestations of caring behavior, self-maintenance and neglecting behaviors as well as the pup retrieval test, no strain-independent effect of the GR mutation was noted. However, an interaction between GR genotype and licking/grooming behavior was observed: it was down-regulated in heterozygous C57BL/6 mice to the level recorded for Balb/c mice. Home cage observation poses minimal disturbance of the dam and her litter as compared to more invasive assessments of dams' emotional behavior. This might be a reason for the absence of any overall effects of the GR mutation, particularly since GR heterozygous animals display a depressive-like phenotype under stressful conditions only. Still, the subtle effect we observed may point towards a role of GR in postpartum affective disorders

Memory score.

<p>The memory score was based on correct and incorrect arm entries during the test phase only. Data are presented separately for the four experimental groups as means ± standard error of the mean.</p

DSWS testing procedure.

<p>The DSWS test consisted of a training and a test phase separated by a delay that was either 30 seconds or 15 minutes long.</p

Measures assessed during the habituation phase.

<p>We recorded the average number of fruitloops retrieved, arms visited and faecal boli dropped of cNLH and cLH rats during the habituation phase of the delayed spatial win-shift test. Data are presented as means ± standard error of the means.</p

Total test time.

<p>The total time needed to complete a trial included both the training and the test phase. Data are averaged across three consecutive trials and presented separately for the four experimental groups as means ± standard error of the mean.</p

Learning measures.

<p>(<b>A</b>) The amplitude and (<b>B</b>) learning maximum were calculated on the basis of individual learning curves. Data are presented separately for the four experimental groups as means ± standard error of the mean, *p<0.05.</p