Behavioural, neurochemical and neuroendocrine effects of predator stress in mice

Stress plays a role in the etiology of anxiety and mood disorders.
To investigate these disorders, animal models are used, many of
which incorporate a stressful stimulus. Especially psychological
stressors may resemble stressful situations that in humans can lead
to pathology. The study, described in this thesis, was undertaken
to elucidate the effects the psychological stressor predator
exposure has on behaviour, on neurochemical parameters in various
brain regions and on neuroendocrine parameters in mice. Therefore
mice of several strains were exposed to a rat. Also the effects of
repeated predator exposure were assessed. Rat exposure lead to risk
assessment behaviour, followed by coping strategies. Extracellular
levels of serotonin and its metabolite were higher than baseline
levels in the hippocampus, prefrontal cortex, lateral septum, but
not in the caudate putamen. Also the levels of noradrenaline were
clearly increased in the hippocampus. Plasma concentrations of ACTH
and corticosterone were mildly elevated in three out of five
examined strains. These strains also exhibited a slightly different
behavioural profile. With re-exposure, less risk assessment took
place, levels of free corticosterone were lower, but hardly any
differences in neurochemical parameters were seen. Taken together,
behavioural, neurochemical and neuroendocrine parameters form a
complimentary picture indicating that rat exposure in its current
form had mild arousing properties. Also in this mild form predator
exposure elicited a selective activation of brain regions and
neurochemicals. This highly differentiated response may be of
utmost importance to coordinate and to fine-tune the specific
neuroendocrine, behavioural and autonomic responses to this form of
stress. It might be worthwhile to increase the stressful properties
of the paradigm to further look into these mechanisms.