Effects of rat odour and shelter on maternal behaviour in C57BL/6 dams and on fear and stress responses in their adult offspring

Recent studies in rats and mice suggest that developmental plasticity of HPA-stress and fear responses could be mediated by environment-dependent variations in maternal behaviour. The present study was designed to examine this question further by varying the adversity of the maternal environment to study its effects on nest-attendance and maternal care and on the HPA and fear responses in the adult offspring. C57BL/6 dams and their litter were housed in a cage system composed of a nest cage (NC) and a foraging cage (FC) connected by a tunnel. Using a 2 X 2 factorial design, we varied the maternal foraging environment (FC) by the presence or absence of rat odour (feces) and shelters (MouseHouse and tube) from postnatal days 1-14 and assessed the adult offspring's corticosterone response to isolation/novelty stress and their behaviour in three tests of fearfulness (elevated-O-maze, open-field, free exploration). While the presence of shelters in the FC reduced time spent in the NC (nest site attendance), the presence of rat odour in the FC increased active maternal care without altering nest site attendance. Alterations of the offspring's HPA and fear responses were rather subtle. The presence of shelters in the dam's foraging environment decreased fearfulness in the offspring in the free exploration test. In addition, males reared by dams exposed to rat odour were less fearful in the open-field test, and both males and females reared by dams without shelters and rat odour in the FC showed a greater corticosterone response to isolation/novelty stress. Multiple regression analysis indicated a negative relationship between maternal licking/grooming and fearfulness in males and a positive relationship between nest site attendance and fearfulness in females. Taken together, these results indicate that mouse darns adjust specific aspects of maternal behaviour in response to the specific properties of their environment, and that active maternal care and nest site attendance are two aspects of maternal behaviour that may affect the offspring's stress and fear systems independent of each other and in a sex-specific way. (C) 2008 Elsevier Inc. All rights reserved.