INDEPENDENT SEGREGATION OF A HYPERACTIVE HYPOTHALAMIC-HYPOPHYSO-ADRENAL AXIS AND A REDUCED BEHAVIORAL REACTIVITY IN PIGS

When compared to European Large White, Chinese Meishan pigs have high levels of circulating ACTH and cortisol, and a reduced behavioural rea ctivity in various challenging situations such as exposure to a novel environment, two characteristic features of depression. We investigate d whether this association is genetically built in or whether these ps ychobiological characteristics are fortuitously associated. Six-week-o ld piglets from the segregating F2 crosses between the Meishan and Lar ge White breeds were studied in a standardised protocol of novel envir onment exposure. As expected from the genetic diversity, a wide range of variation was recorded for behavioural reactivity (locomotion, voca lisations). ACTH, cortisol, and glucose were measured in blood samples taken immediately before the test and at the end of the session. Agai n these measures varied considerably between animals, and the continuo us distribution of the scores suggested that they are under control of numerous genes. Furthermore, no correlation could be found between ne uroendocrine and behavioural measures. This result demonstrates that t he association between high ACTH/ corticosteroid levels and a low beha vioural reactivity is not genetically controlled.