Endocrine Abstracts

Early life events can have short and long-term effects on neuroendocrine, autonomic, and behavioural responses to stress and appear to play an important role in the etiology of stress-related disorders. Glucocorticoids are thought to be key mediators of these brain-endocrine-immune connections. We investigated the effects of a short-term social isolation (4 h) of domestic piglets at different days of age (7, 21, 35) both on behavioural alterations in open-field tests and on modifications in the expression of genes regulating glucocorticoid response in stress-related brain regions. Evaluation of glucocorticoid receptor (GR), mineralocorticoid receptor (MR), 11β-hydroxysteroid dehydrogenase 1 and 2 (11β-HSD1 and 11β-HSD2) mRNA expression by real-time RT-PCR revealed significant differences in quantity of these genes in hypothalamus, hippocampus and amygdala. The social isolation caused a significant increase in ACTH and cortisol concentrations and an increase of behavioural arousal. The increased activity of the HPA axis and the behavioural alterations were associated with distinct changes in gene expression in the limbic system. The hypothalamic GR, MR and 11β-HSD1 mRNA levels significantly increased in piglets exposed to isolation stress, whereas in the amygdala the MR mRNA expression significantly decreased. There was also a significant increase of HSD1 mRNA in isolated piglets in hippocampus on day 7 of age, but the 11β-HSD2 mRNA levels were not influenced by social isolation in the brain regions. In conclusions, psychosocial stress in form of a short-term social isolation in piglets caused age-dependent and region-specific modifications in mRNA levels of stress-related genes in the brain accompanied by changes in open-field behaviour indicating adaptive arousal and experienced distress. Therefore, we suggest that psychosocial stress effects should be considered in livestock handling practices (e.g. the weaning of piglets).