Endocrine and behavioural comparisons of male mice under semi-natural and caged conditions

Abstract

The work of this thesis wes based on Investigations froa previous conventional cage studies which examined the characteristics of dominant and subordinate male mice. It was predicted that high status males would have high testosterone output and heavy sex accessory glands but would also have low corticosterone output and adrenal weights. By contrast, It was expected that subordinate mice, by virtue of their social position, would be chronically stressed due to continual threat of attack and Injury, and adrenal activity would be raised In this group. Raised blood urea levels and pain thesholds as further evidence of stress, were also predicted.
Hackintosh (1970) demonstrated that given adequate space, male mice could establish territory areas under laboratory conditions. As a consequence, the predictions above were tested on mice housed In both traditional laboratory cages and within the more open environment of a free range room. It was also predicted that high status mice from both these forms of housing would possess an aversive urinary odour cue and a urine marking pattern of dense spots, neither of which would be characteristics of low status males.
Among subordinate animals, evidence was found for acute but not chronic social stress so that the predictions for these males were not upheld. Other results showed that In high status males gonadal activity was not always raised over time, particularly among free range territory holders. Testosterone levels In this group notably decreased over experimental periods. It was concluded that the role of this androgen is largely permissive In maintaining status and territory with only low levels are required. Results are discussed in terms of the advantages this might have for mice in colonies under more natural but confined conditions.
The existence of an aversive cue did not always correlate
positively with a particular marking pattern, nor with testosterone output, although it did correlate with territorial status. Overall, the results suggest that too strong a correspondence may have previously been drawn between androgen output and these urinary traits.