Behavioral and cognitive profile of mice with high and low exploratory phenotypes.

Temperament is the heritable and relatively stable pattern of basic emotions, such as fear and anger. We explored behavioral features in mice to select distinct phenotypes with extremes of temperament. In a new environment (open-field) with a central object, two groups of 15 mice from 79 screened were separated according to high or low exploration of the object to compose the high and low exploratory groups, respectively. Their performance was mostly identical in the same task 1 week later and still distinguishable 8 months later, suggesting the presence of trait or temperamental features. These mice were further tested in other behavioral tasks. Compared to low exploratory mice, high exploratory mice were less anxious in the light/dark task and the elevated plus maze, showed increased locomotion in an open-field, improved their performance along trials in the Lashley maze (with appetitive stimulus) and had higher latency to step-down in the inhibitory avoidance task (with aversive stimulus). High exploratory mice were aggressive in the intruder test, whereas low exploratory mice were non-aggressive or submissive. These results show that individual differences in temperament influence a range of behaviors in mice. The behavioral profile of low and high exploratory mice resembled the depressive and hyperthymic temperaments of patients with unipolar depression and bipolar disorders, respectively, which may be relevant for modeling mood disorders.