Resilience and Vulnerability in a Model of Early Life Stress

Abstract

Exposure to early life stress (ELS) is a major contributor to the development of psychiatric disorders, yet the neural pathways that translate these experiences into lasting vulnerability remain mostly unknown. In this thesis, the limited bedding and nesting (LBN) model in rodents was used to induce ELS by restricting the dams' access to nesting material during the early postnatal period. This manipulation is known to disrupt maternal care and expose pups to a stressful environment. To assess the lasting impact of these early experiences, a behavioural battery was employed, which includes the Open Field Test (OFT), Elevated Plus Maze (EPM), Novel Object Recognition (NOR), a social interaction task (SI), and a cue-association task. Additionally, we assess the stress response induced by social interaction with an unfamiliar conspecific by measuring the levels of corticosterone. Behavioural analysis in the OFT revealed that animals reared under LBN conditions spent significantly more time in the centre (p < 0.05) compared to CTRLs. In contrast, no significant group differences emerged in the EPM. Interestingly, results in the two tasks, which commonly assess anxiety-like behaviour, were inversely correlated, underscoring the role of context-specific behavioural expression and highlighting interindividual variability. During SI, the LBN group exhibited an increased preference for unfamiliar conspecifics compared to the CTRL group (p < 0.05). Moreover, LBN males' corticosterone levels increased after the SI more strongly than seen in CTRL males (p<0.05). These findings demonstrate that ELS can alter behaviour in a context-dependent manner and modulate stress reactivity in a sex-specific fashion. Upcoming experiments will further investigate these behavioural outcomes linked with neuronal recordings.