Early life stress is a known risk factor for psychological disorders including anxiety, depression and cognitive impairment. Examining underlying mechanism(s) is challenging in the human, thus several animal models have been developed, most recently limited nesting (LN), which is thought to reflect the human condition where the mother is present but care is fragmented(1). Here, we used the LN model in the rat to examine the impact on anxiety and cognition in female Sprague Dawley rats. Rat pups and their dams were provided with a metal grid floor and half a paper towel, from postnatal days 2-9, thereby creating a harsh early environment for the pups and dams, versus control rats with normal bedding. Anxiety-like behaviour was assessed at 5 weeks of age using elevated plus maze and the novel object and place memory were assessed at 6 weeks of age with the novel object and place tasks.
Our data reveal that LN did not induce anxiety-like behaviour. No effect on spatial memory in LN pups as assessed with novel place task was observed in LN pups. Interestingly, LN pups showed more than double the exploration time for a novel object compared to control (42.29 ± 5.61 vs 19.32 ± 2.71, p<0.001) and they had a significantly increased exploration ratio (0.72 ± 0.04 vs 0.59 ± 0.04, p=0.01). Hippocampal gene expression measured at 15 weeks demonstrated LN females had significantly reduced expression of neurotrophic genes such as reelin and neuromedin 1 mRNA (p< 0.05).
In summary, LN female pups appeared to be resilient to the effects of LN induced early life stress, with no evidence of increased anxiety-like behaviour. Moreover they showed improved recognition of a novel object but not place. Reduced expression of neurotrophic markers may develop vulnerability for neurodegenerative disease later in life.