Characteristics of coping behavior of rats exposed to a long-term hardly escapable aversive stimulus: a possible depression model

Effects of Valerianae Radix et Rhizoma extract on psychological stress in mice

Background:

The aim of this study was to identify the effects of Valerianae Radix et Rhizoma water extract (VRe) originated from Valeriana fauriei Briquet on reducing psychological stress (PS) on mice.

Objective:

Mice were put under PS with communication box method: Restraining mice and forcing to see other mice underfoot shock stress.

Materials and Methods:

Measurements on plasma corticosterone, noradrenaline and lipid peroxidation, and elevated plus-maze (EPM) tests were carried out to determine the effect of VRe administration on physiological and behavioral responses of mice.

Results:

VRe showed anxiolytic effects in plasma corticosterone, noradrenaline, and EPM transfer latency levels, but it did not show any significant effects on the other indicators.

Conclusion:

V. fauriei, which has been used as a natural anxiolytic drug, exerts positive effects in the communication box induced PS in mice.

An extract from wild green oat improves rat behaviour

An extract of wild green oat (Avena sativa L.), was tested in vivo in rats for its behavioural effects after chronic oral administration via extract-admixed food. Thirty six male Sprague-Dawley rats received (A) standard diet (controls), (B) 10 g/kg extract-admixed food or (C) 100 g/kg extract-admixed food. The following behavioural tests were performed: elevated plus maze, forced swimming, conditioned avoidance response and tetradic encounter. Body weight, food and fluid consumption were measured and apparent physical appearance was determined twice a week. Apart from a slightly decreased food and fluid intake in the high dose group there were no side effects observed during the treatment. The low dose led to an improvement of active stress response, an enhancement of shock avoidance learning and an increased synchrony in social behaviour. It may be concluded that the wild green oat extract is suitable to improve behavioural initiative in different situations.

Physical but not emotional stress induces a delay in behavioural coping responses in rats

Physical stress (PS) and emotional stress (ES) have opposite long-term effects on open field behaviour. PS consisted of a repeated mild foot shock treatment, which the ES animals witnessed. PS caused a long-term decrease in locomotor activity and exploration behaviours and increased immobility. ES induced an increase in locomotor activity. These changes in open field behaviour could be the result of several factors such as increased anxiety, a shift in coping strategy or simply a change in locomotor activity. To investigate the effect of the PS and ES treatment on these separate factors, the following behavioural tests were performed: defensive withdrawal, shock prod bury, large open field and social interaction. PS animals initially showed immobility in the shock prod bury test and the large open field, while the differences measured over the entire test period were small or not present. PS did not induce differences in the defensive withdrawal and the social interaction tests. ES and control animals did not differ significantly in any of the tests. The effects of PS in the shock prod bury test in particular can be interpreted as an indication of a passive coping style. However, PS animals showed the same behaviour as controls, but started displaying the behaviour after the initial immobility response. It is concluded that neither PS nor ES affects the coping style and anxiety level of the rats. PS induces a delay in behavioural responding and ES induces locomotor activation per se. It seems that the shock prod bury test is most suitable to distinguish between exploration and coping style.

Evaluation of depression in rats exposed to chronic (unpredictable) electric shock

The present study was undertaken to evaluate the applicability of a proposed behavioral stress paradigm as an animal model for depression. Rats were trained to press a lever under a fixed ratio (FR) 5 schedule in a Skinner box for 10 days and were subsequently exposed to a daily regimen of 20 cycles of FR 5 and 10 cycles of variable ratio (VR) 10 for about a week. This exposure resulted in a reduction of the number of lever presses and successful escapes compared to the level achieved after training. In addition, weight gain was significantly suppressed compared with other treatments. Acute and chronic administration of psychotropic drugs (imipramine and chlordiazepoxide) showed that treatment with imipramine increased both the number of lever presses and successful escapes while chlordiazepoxide increased only the number of lever presses. The results suggest that this simplified animal model utilizing chronic unpredictable electric shock may be useful in the study of human depression.