Independent segregation of a hyperactive hypothalamic-hypophyso-adrenal axis and a reduced behavioural reactivity in...

When compared to European Large White, Chinese Meishan pigs have high levels of circulating ACTH and cortisol, and a reduced behavioural reactivity in various challenging situations such as exposure to a novel environment, two characteristic features of depression. We investigated whether this association is genetically built in or whether these psychobiological characteristics are fortuitously associated. Six-week-old piglets from the segregating F2 crosses between the Meishan and Large White breeds were studied in a standardised protocol of novel environment exposure. As expected from the genetic diversity, a wide range of variation was recorded for behavioural reactivity (locomotion, vocalisations). ACTH, cortisol, and glucose were measured in blood samples taken immediately before the test and at the end of the session. Again these measures varied considerably between animals, and the continuous distribution of the scores suggested that they are under control of numerous genes. Furthermore, no correlation could be found between neuroendocrine and behavioural measures. This result demonstrates that the association between high ACTH/corticosteroid levels and a low behavioural reactivity is not genetically controlled.