Impact of individual trait for emotionality on behavioural, physiological and neurobiological consequences of chronic stress in birds

International audienceThere is considerable variability in the susceptibility of individuals to the adverse effects of chronic stress. In humans and other mammals, individual traits such as high anxiety are proposed as a vulnerability factor for the development of stress-related disorders. In the present study, we tested whether a similar behavioural trait in birds, a higher emotional reactivity, also favours the occurrence of chronic stress related behavioural, physiological and neurobiological dysfunctions. For this, two lines of Japanese quail divergently selected for the duration of tonic immobility, a typical fear response in birds, were subjected to unpredictable aversive stimulations over 2 weeks. Previous studies demonstrate that the selection program modifies the general underlying emotionality of the birds rather than exerting its effect only on tonic immobility. Chronic stress was associated with severe changes both at the physiological and behavioural level. Indeed, stress birds displayed decreased body weight, started laying later and decreased basal corticosterone level in comparison with control non stressed birds. Behaviourally, chronic stress enhanced anxiety behaviours during the open field test, the novel object test and a food neophobia test. Stressed birds were also more inactive in a restraint box suggesting potential effect of the stress treatment on behaviours related with resignation. Current investigations are under process to unravel the impact of chronic stress on social behaviours and neurobiological functions. Interestingly, the effects of chronic stress on anxiety behaviours in the open field test and on basal corticosterone level were more severe in birds selected for their higher emotionality. These findings thus highlight emotional reactivity as an important predisposing factor for the occurrence of the adverse effects of chronic stress in birds