Environmental determinants of behavioural responses to short-term stress in rats: Evidence for inhibitory effect of ambient landmarks

Abstract

Behavioural responses to stress occur in an environment-dependent manner. Complex environments require flexible behavioural coping strategies and chronic stress usually generates psychomotor inhibition. Here, we examine if short-term stress also exerts an inhibitory effect on novelty-seeking, exploratory behaviours. Rats underwent acute restraint stress or were left undisturbed, and their neuroendocrine and behavioural responses were assessed at short- and long-term time points. Animals were individually tested in the open field task (OFT) and the corridor field task (CFT) with and without a central object for free exploration and novelty seeking behaviour. Stress-related psychomotor alterations were measured by path speed, path length, number of stops and thigmotaxis in both tasks. Short-term stress activated the hypothalamic-pituitary-adrenal axis causing elevated plasma corticosterone levels. Stress also impacted psychomotor functions in terms of motivational changes (higher speed and longer path) only in the central-object variations of the OFT and CFT. Moreover, stress-induced emotional alterations were manifested by a higher number of stops and thigmotactic behaviour only in the central-object condition. These findings suggest that environmental landmarks determine the type and direction of exploratory behaviour under transient stress.

Keywords: Acute stress; Chronic stress; Corridor field task; Corticosterone; HPA axis; Home base behaviour; Hypothalamic-pituitary-adrenal axis; Novelty-seeking behaviour; Open field task.