Sexual dimorphism in rats: effects of early maternal separation and variable chronic stress on pituitary-adrenal axis and behavior

The pituitary-adrenal axis response is gender-dependent, showing lower activity in male rats. Furthermore, males showed low emotional behavior and females high emotionality when exposed to such chronic stress situations.The gender of an animal is a relevant factor in the development of responses to stress. The aim of the present study was to investigate the influence of early maternal separation on the pituitary-adrenal activity and emotional behavior of adult male and female rats subjected to chronic variable stress. Male and female Wistar rats were isolated 4.5 h daily, during the three first weeks of life. At 48 days of age, the rats were exposed to variable chronic stress (five different stressors during 24 days). Non-maternally separated and maternally separated males showed lower levels of ACTH compared to females (p < 0.01). In male rats exposed to variable chronic stress, the maternally separated animals showed a diminution in the levels of ACTH and Corticosterone (p < 0.05) compared to non-maternally separated rats. In the Open Field test, the maternally separated and non-maternally separated-stressed males showed lower emotional reactivity compared with female rats. This was indicated by increase in ambulation (p < 0.05) and decrease in defecation (p < 0.05). Male rats subjected to variable chronic stress presented low emotional behavior seen in their lower defecation (p < 0.05). Stressed females displayed decreased ambulation (p < 0.05) and increased defecation (p < 0.05), showing high emotional reactivity after exposure to chronic stress. Maternally separated males showed higher emotionality after the exposure to chronic variable stress. This was indicated by decrease in ambulation (p < 0.05), decrease in rearing (p < 0.05) and increase in defecation (p < 0.05). Thus, maternal separation and variable chronic stress caused long-term gender-dependent alterations in pituitary-adrenal activity and emotional behavior.