This thesis examined the influence of hormones of the pituitary-adrenocortical axis ('stress hormones') and gonadal steroids on intra-specific intermale fighting in the house mouse (Mus musculus L.). Experiments were described which investigated both acute and chronic effects of stress hormones on aggressive motivation. These involved administration of ACTH, ACTH analogues (peptide fragments of the ACTH molecule), dexamethasone and corticosterone to intact or adrenalectomised animals. Studies concerning gonadal steroids involved administration of cyproterone acetate (an anti-androgen) to male and female mice in early life while others were designed to determine the relevance of the 'aromatisation hypothesis' (i.e. that androgens are converted to oestrogens before exerting behavioural effects) to intermale fighting between mice. The latter experiments involved administration of oestradiol benzoate, 19-hydroxytestosterone, androstenedione, testosterone and 5 x dihydrotestosterone to adult castrated males. Results indicated that chronically, activation of the pituitary-adrenocortical axis attenuated fighting behaviour - an effect apparently mediated by ACTH. Acutely, aggressive behaviour was enhanced - an effect apparently mediated by corticosterone. These effects were thought to be independent of the pituitary gonadal axis, not the result of gross changes in motor activity and unrelated to changes in sensory cues e.g. olfactory signals. Cyproterone acetate did not block the 'androgenisation' of the CNS in early life but appeared to act as a weak androgen. The aromatisation hypothesis was supported by findings that oestrogens were at least as effective as androgens in maintaining aggressive motivation and that 19-hydroxytestosterone (an intermediate between testosterone and 17/3 oestradiol) was also effective. However, aromatisation of the steroid 'A' ring did not appear to be an essential prerequisite for behavioural action since 5x dihydrotestosterone, which cannot be aromatised, also maintained fighting to some extent. Hormonal influences on aggressive behaviour investigated were disussed in terms of possible contributions to the biological fitness of individuals. Findings were also briefly related to current medical research.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:636919 |
| Date | January 1980 |
| Creators | Evans, A. E. |
| Publisher | Swansea University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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