Late maternal separation provides resilience to chronic variable stress-induced anxiety- and depressive-like behaviours in male but not female mice.

Maternal separation can have long-lasting effects on an individual's susceptibility to stress later in life. Maternal separation during the postnatal period is a commonly used paradigm in rodents to investigate the effects of early life stress on neurobehavioural changes and stress responsiveness. However, maternal separation during stress hyporesponsive and responsive periods of postnatal development may differ in its effects on stress resilience. Therefore, we hypothesised that late maternal separation (LMS) from postnatal day 10 to 21 in mice may have different effect on resilience than early maternal separation during the first week of postnatal life. Our results suggested that male LMS mice are more resilient to chronic variable stress (CVS)-induced anxiety and depressive-like behaviour as confirmed by the open field, light-dark field, elevated plus maze, sucrose preference and tail suspension tests. In contrast, female LMS mice were equally resilient as non-LMS female mice. We found increased expression of NPY , NPY1R , NPY2R, NPFFR1, and NPFFR2 in the hypothalamus of male LMS mice whereas the opposite effect was observed in the hippocampus. LMS in male and female mice did not affect circulating corticosterone levels in response to psychological or physiological stressors. Thus, LMS renders male mice resilient to CVS-induced neurobehavioural disorders in adulthood.