Chronic gestational stress affects behaviour in lactating rats and has implications on the physiology of the offspring

Maternal adaptations like decreased anxiety and an attenuated stress-responsiveness are necessary to enable successful post-natal protection and nurturance of the offspring. Furthermore, there is growing evidence that these adaptations are also required to protect the mother. In order to asses the relevance of such adaptations we developed a chronic pregnancy stress paradigm and examined its impact on behavioural parameters in lactating dams and virgins as well as physiological and behavioural parameters in the offspring. Stressed rats were housed in cages of 5 until pregnancy day (PD) 4at which point they underwent alternative restraint stress (2×1h) and overcrowding with unfamiliar females until PD16. Verification of the stress paradigm was achieved by revealing a significantly lower body weight gain and increased adrenal weight in all stressed groups relative to their respective unstressed controls. While stress exposure did not alter the behaviour of the virgins in the elevated plus maze and the light dark box, it abolished the lactation-induced anxiolysis in the lactating dams. Moreover, chronic pregnancy stress altered maternal behaviour, causing the dams to spend more time in direct pup contact and arched back nursing until mid-lactation. Chronic gestational stress did not only affect the lactating dams, it also had implications on the offspring's physiology. While there was no difference between prenatal stressed and non-stressed offspring in body weight at the time of birth or pup litter size, a significant weight difference was observed on lactation day (LD) 2 and LD6-LD8, as well as a gender specific weight difference from week 4- week 12. Additionally, prenatal stress led to an increase of ultrasonic calls in the pups. Thus, this chronic psychosocial stress paradigm has revealed important consequences of gestational stress on maternal and offspring behaviour and physiology.