Synergistic impact of early-life stress and prenatal immune activation on spatial memory and oxidative metabolism in rat cortico-limbic networks

Abstract

Early life exposure to immune activation and stress are critical factors involved in the development of mental and neurodevelopmental disorders in adulthood. This study explored the individual and combined effects of prenatal lipopolysaccharide-induced (LPS)-induced immune activation and postnatal maternal separation on cognitive performance and oxidative metabolism in male Wistar rats. Using a 2 × 2 factorial design, pregnant dams were exposed to LPS or saline on gestational day 15, and offspring underwent maternal separation from postnatal days 2–14. In adulthood, cognitive function was assessed using the Morris Water Maze, and regional brain energy metabolism was evaluated using quantitative histochemistry of cytochrome c oxidase (CCO) quantitative histochemistry in the prefrontal cortex, hippocampus, and retrosplenial cortex.

Rats exposed to both stressors demonstrated significant impairments in spatial memory and cognitive flexibility, supporting the “two-hit” hypothesis of early adversity, which posits that early life exposure to an adverse environmental event (first hit) combined with subsequent exposure to stress during critical developmental periods (second hit) can significantly increase the risk of developing behavioral or neurodevelopmental disorders in adulthood. Accordingly, adult animals exposed to prenatal LPS and maternal separation showed prolonged escape latencies and decreased spatial memory retention during the behavioral tasks. Concurrently, CCO activity was markedly increased in all measured regions, reflecting heightened metabolic demands. These changes are consistent with impaired hippocampal-prefrontal-retrosplenial network integration and the underlying key processes involved in cognitive alterations such as memory or attention.

This study underscores the synergistic effects of these environmental factors on cognitive and metabolic dysfunction, providing a translational model to better understand the etiology of neurodevelopmental disorders. The findings highlight the importance of addressing multiple interacting environmental factors in the context of early life adversity.