Modulating the effects of chronic stress through increasing the activity of the adrenergic system

Noradrenergic system is involved in stress and anxiety related behaviors. The neural pathways of stress and the noradrenergic system in the hippocampus have a reciprocal effect on each other. Therefore, in this study, the effect of noradrenergic activity on anxiety and learning under stress conditions is investigated.

Adult male Wistar rats weighing 180-230 were given acute (3 days) or chronic (21 days) restrained stress. Yohimbine was injected with a dose of 2 mg/kg (intraperitoneally) to activate the noradrenergic system. After 24 hours from the last stress session, social learning and then anxiety and exploratory behavior and new object recognition were investigated in animals.

The amount of association with a familiar rat (stranger 1) decreased due to acute (p < 0.01) and chronic
(p < 0.001) stress and increased with a stranger rat (stranger 2). The time in the open arm of the elevated plus maze decreased (p < 0.001) due to acute and chronic stress, and animals receiving yohimbine, while the time increased
(p < 0.001) in the closed arm. The duration of immobility in the open field test increased due to acute (p < 0.01) and chronic (p < 0.001) stresses, while it decreased after yohimbine administration in the chronic (p < 0.001) stress group. The time spent with the familiar object was increased (p < 0.001) by chronic stress and decreased (p < 0.001) by acute stress and yohimbine administration.

This study showed that increasing the activity of the noradrenergic system moderates the effects of chronic stress, which indicates the possible cooperation of the glucocorticoid and adrenergic systems.