PhD‐theses - Ethologische Gesellschaft

Research Update
HOME SWEET HOME – THE INFLUENCE OF HOUSING CONDITIONS ON STRESS PHYSIOLOGY,
COGNITION AND EMOTIONAL BEHAVIOUR IN MICE SELECTIVELY BRED
FOR EXTREMES IN STRESS REACTIVITY
Britta Schindler
britta.schindler@gmx.net
Diploma thesis, supervised by Dr. Chadi Touma, Max Planck Institute of Psychiatry, Research Group
of Psychoneuroendocrinology, Kraepelinstr. 2‐10, D‐80804 Munich
It has repeatedly been shown that environmental factors can substantially affect the
phenotype of an individual, including social behaviour, changes of body and organ weight as
well as neuroendocrine parameters. Furthermore, it has been reported that specific brain
regions such as the hippocampus, which is important for learning and memory, are also
influenced by the environment. An ideal system to study these gene‐environment
interactions is to make use of animal models that show a strong genetic predisposition for
certain endophenotypes. Such a model was recently established in our group. This ‘stress
reactivity’ (SR) mouse model consists of three independent mouse lines selectively bred for a
high (HR), intermediate (IR) or low (LR) secretion of corticosterone from the adrenals in
response to a standardised, psychological stressor (15‐min restraint), i.e. showing a hyper‐ or
a hypo‐reactivity of the hypothalamic‐pituitary‐adrenocortical (HPA) axis.
The goal of the present study was therefore to investigate the impact of non‐social
environmental factors such as different housing conditions on specific phenotypes of the SR
mouse model. Of each breeding line, 32 juvenile males were divided into two groups and
kept in groups of four, either under enriched (EN) or standard (ST) housing conditions. In
addition to the bedding and nesting material provided in the ST cages, the EN cages were
equipped with a shelter, a wooden climbing frame as well as with extra bedding and nesting
material. In order to analyse potential differences in the agonistic, socio‐positive and play
behaviour as well as in general activities, we recorded the home cage behaviour of the
animals at three time points (once per week during the first hour of the light phase).
Furthermore, we monitored the body weight of the animals, food intake and coat status to
document the welfare of the animals as well as changes in energy metabolism. After
exposing the animals for six weeks to the respective housing conditions, they were subjected
to a battery of behavioural tests assessing their emotionality, including explorative drive
(open field test, OF), anxiety‐related behaviour (elevated plus‐maze test, EPM) and stress
coping behaviour (forced swim test, FST). Moreover, spatial learning abilities were assessed
in the Y‐maze test and potential effects on HPA axis reactivity were analysed by subjecting
the animals to a ‘stress reactivity’ test (SRT).
The results of our experiment revealed that housing under enriched conditions
influenced several behavioural and neuroendocrine parameters in the SR mouse model.
Compared to ST housed animals, EN housed mice of all three lines showed a higher variety
of behaviours performed in the home cage and significantly less agonistic interactions were
observed. This coincided with decreased corticosterone levels in HR‐EN mice immediately
before the SRT, although the corticosterone response to the stressor was not influenced and
the characteristic HPA axis reactivity differences between HR, IR and LR mice persisted in
both housing conditions. Similarly, stress coping behaviour in the FST was modified towards
more active coping under EN housing conditions (more ‘struggling’ in IR mice and less
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