Introduction: Maternal separation (MS) is a widely recognized paradigm that can be employed to investigate the physiological effects of stress experienced during early life. During the first two weeks of life, daily maternal separation plays a crucial role in the development of the hypothalamic–pituitary–adrenocortical (HPA) axis, a significant neuroendocrine system that responds to environmental stressors. Prior research has indicated that MS has demonstrated that the plasticity of the central nervous system in childhood renders it vulnerable to stress in adulthood. Early maternal separation in adult mice leads to increased stress responsiveness, resulting in elevated glucocorticoid levels after acute or chronic stress. However, the effects of late MS (LMS) on HPA axis during adolescence have not been studied. Hence, aim of the current investigation was to examine the effects of late maternal separation (LMS) on neurobehavioral changes and stress responsiveness during adolescence.

Methodology: Swiss Albino male and female pups from LMS group were daily removed from their home cage for 3 hours from PND 10 to PND 21 between 14:00 h – 17:00 h. After 3 hours of maternal separation, the pups were returned to their home cage. At PND 22, both non-maternal separation group (NMS) and LMS mice were separated and housed together with littermates of the same sex. At PND 56, each mouse from NMS and LMS group were subjected to one chronic variable stress (CVS) randomly for 21 days – (a) overnight fasting; (b) 30 min of restraint stress; (c) shaking for 30 min at 80-100 rpm; (d) placed in ice cold water for 15 min (only paws); (e) placed on a hot surface for 30 min at 400C; (f) isolated and kept in a separate cage; (g) swimming for 5 min. After this period, each mouse was subjected to a series of behavioural tests for five consecutive days that comprised of sucrose preference test, open field test, light-dark box test, elevated plus maze test, and tail suspension test (TST).

Results: Behavioral tests suggested that male LMS mice are more resilient to chronic variable stress (CVS)-induced anxiety and depressive-like behavior, 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 mice without maternal separation. We found an 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 makes male mice resilient to CVS-induced neurobehavioral disorders in adulthood.

 Conclusion: LMS from PND10-PND21 provides resilience to anxiety and depression in male mice, while there were no significant changes in female mice. Our study indicated the role of two neuropeptides, Npy and Npvf, and their receptors in stress resilience to CVS-induced anxiety- and depression-like behavior in male LMS mice.