Vulnerability to chronic subordination stress-induced depression-like disorders in adult 129SvEv male mice.

Exposure to stressful life events is intimately linked with vulnerability to neuropsychiatric disorders such as major depression. Pre-clinical animal models offer an effective tool to disentangle the underlying molecular mechanisms. In particular, the 129SvEv strain is often used to develop transgenic mouse models but poorly characterized as far as behavior and neuroendocrine functions are concerned. Here we present a comprehensive characterization of 129SvEv male mice's vulnerability to social stress-induced depression-like disorders and physiological comorbidities. We employed a well characterized mouse model of chronic social stress based on social defeat and subordination. Subordinate 129SvEv mice showed body weight gain, hyperphagia, increased adipose fat pads weight and basal plasma corticosterone. Home cage phenotyping revealed a suppression of spontaneous locomotor activity and transient hyperthermia. Subordinate 129SvEv mice also showed marked fearfulness, anhedonic-like response toward a novel but palatable food, increased anxiety in the elevated plus maze and social avoidance of an unfamiliar male mouse. A direct measured effect of the stressfulness of the living environment, i.e. the amount of daily aggression received, predicted the degree of corticosterone level and locomotor activity but not of the other parameters. This is the first study validating a chronic subordination stress paradigm in 129SvEv male mice. Results demonstrated remarkable stress vulnerability and establish the validity to use this mouse strain as a model for depression-like disorders.

The suitability of 129SvEv mice for studying depressive-like behaviour: both males and females develop learned helplessness.

Behavioural studies using transgenic techniques in mice usually require extensive backcrossing to a defined background strain, e.g. to C57BL/6. In this study we investigated whether backcrossing can be replaced by using the 129SvEv strain from which the embryonic stem cells are generally obtained for gene targeting strategies to analyze e.g. depression-like behaviour. For that purpose we subjected male and female 129SvEv mice to two frequently used depression tests and compared them with commonly used C57BL/6 mice. 129SvEv and C57BL/6 mice exhibited differing profiles with regard to locomotion and pain sensitivity. However, in the learned helplessness paradigm, a procedure, which represents a valid method to detect depressive-like behaviour, 129SvEv animals develop a similar level of helplessness as C57BL/6 mice. One great advantage of the 129SvEv animals though, is the fact that in this strain even females develop helplessness, which could not be produced in C57BL/6 mice. In the tail suspension test, both genders of 129SvEv exhibited more despair behaviour than C57BL/6 animals. We therefore suggest that this strain may be utilized in the establishment of new test procedures for affective diseases, since costly and time-consuming backcrossing can be prevented, depressive-like behaviour may be analyzed effectively, and gender-specific topics could be addressed in an adequate way.