Social stress in female mice: effects of differential housing on adrenocortical activity and the oestrous cycle

Abstract

The general aim of this study has been to examine some physiological and behavioural aspects of crowding in mice. The notion of stress has been central to this study. Using Selye's General Adaptation Syndrome hypothesis as a framework, modern ideas of stress have been re-examined. Social stress and population regulation in the house mouse have been reviewed. It'has been concluded that social factors can regulate mouse populations and that it can be female reproductive productivity that is limiting. Little is known about the social behaviour of females and, in particular, social stress.
Plasma corticosterone levels in female mice were measured, using radioimmunoassay, as an indicator of stress. Basal plasma corticosterone levels were unaffected by housing density, social stability and some methodological procedures. Small differences in plasma corticosterone between grouped and individually housed mice were found when values of mice sampled.at pro-oestrus were excluded. Pro-oestrus values were almost twice those at other stages of the oes- trous cycle.
The circadian rhythm of plasma corticosterone was not different in grouped and individually housed female mice but stress response levels were higher in the grouped mice after blood sampling and ether but not after ether treatment only. It was concluded that whilst some differences in adrenocortical functioning occur between differentially housed female mice these are not indicative of social stress. Further, the use of adrenocortical activity as an indicator of stress was examined critically.
It was proposed that the failure to replicate the results of "semi-natural" studies in laboratory experiments was due to either genetic strain differences or to the presence of males. Preliminary studies showed that male urine can activate the adrenal cortex in females.
The suppression of oestrus found in grouped females was due to pseudopregnancy and not anoestrus.