Cognitive Effects Of Neonatal Maternal Separation In Prepuberal Male And Female Rats
A growing body of evidence indicates that early life events play a significant role in shaping the behavior and physiology of the adult organism. Repeated maternal separation paradigms, which serve as models for childhood adversity, have yielded permanent physiological, morphological and behavioral changes in adult rats. In studies involving adult animals, a sexually dimorphic pattern has been observed in the cognitive impact of chronic stress paradigms. Male subjects often display cognitive impairments despite a less robust physiological stress response than their female counterparts. Females, on the other hand, often display unaffected or enhanced cognitive functioning. While this effect has been attributed to the neuroprotective effects of estrogen, the present study sought to examine if this dichotomy exists prior to the onset of puberty and thus prior to adult levels of hormones. Male and female Long-Evans rats were separated from the dam and nest for either 15 min (handling) or 180 min (maternal separation) from postnatal days (PND) 2-14. Behavioral testing was carried out between PND 26-39 and included the open field as a measure of anxiety, an object recognition task to assess nonspatial memory, a Y-maze to assess spatial memory, and a water T-maze task to assess learning strategy. No significant effects of sex or treatment were found on the open field. There was also no effect of group or sex on the object recognition test following a 1-hr delay. However, following a 4-hr delay, maternally separated males spent significantly less time with the novel object compared to their handled counterparts, indicating poorer object memory. Meanwhile, maternally separated females spent significantly more time with the novel object as compared to both their handled counterparts and maternally separated males, indicating better object memory. Maternally separated males displayedimpairment on the Y-maze task while maternally separated females showed no effect as compared to controls. All subjects showed a bias toward a response strategy over a place strategy in the water T-maze, perhaps due to age at time of testing. The results of the present study indicate that sex plays a significant role in mediating the cognitive effects of early life stress regardless of the presence of steroid sex hormones.