The effects of physical and psychological stress on the behaviour and neurochemistry of rats
Thesis (MSCMedSc (Biomedical Sciences. Medical Physiology))--University of Stellenbosch, 2005.
Stress is considered one of the major factors involved in the pathogenesis of affective disorders, for example, direct and indirect exposure to terrorist attacks or being subjected to subtle victimization. There is a long history of development of procedures to determine anxiety responses in animals in order to find new or better treatments for patients. Prior stress exposure is known to alter the activation response to a subsequent stressor and the means of coping with stress can influence health and disease. This orchestrated process, usually referred to as the “stress response”, involves various mechanisms, which allow the body to make the necessary physical, psychological and the neuro-endocrine adjustments required to cope with the demands of a homeostatic challenge. The communication box method is a useful model to investigate the physiological changes that occur under psychological stress, since it can produce an experimental anxiety based on psychological communication between two or more animals, without the direct physical stress. In this animal model, the psychologically stressed rats are exposed to the visual, olfactory, auditory stimuli (such as struggling, vocalization, defecating, urinating and jumping) from the foot shock rat (Oishi et al., 2003). In the present study, we examined the neuro-endocrine and behavioural responses after different durations of inescapable foot shock and the subsequent effect of citalopram (10 milligram/kilogram, intraperitoneal once a day for 10 days), a selective serotonin reuptake inhibitor in reversing these responses. We have subjected rats to a number of stress paradigms (varying in duration), and assessed the effects thereof on behaviour at two different time points. Physically stressed rats were subjected to 10 unpredicted electric foot shocks (0.5 milliampere), in 10 minutes, while the psychologically stressed rats witnessed everything. The behavioural responses were assessed 5 days and 10 days after the last stress session. The rats were decapitated and corticosterone concentrations were determined one day after the open field and elevated plus-maze tests were performed. The behavioural and endocrine responses in the rats subjected to physical and psychological stress in this study showed that single stress exposure may lead to different outcomes as repetitive stress exposure and that the consequences of stress exposure develop over time and persist for an extended time period. These consequences of direct stress exposure versus indirect stress exposure show a grading in stress intensity and perception, similar to that observed in humans. In the experiment where the rats where treated with citalopram, it showed that citalopram is effective in reversing anxious-like behaviours, but not locomotor deficits. In all the animals basal plasma corticosterone concentrations were comparable and physically and psychologically stressed rats displayed a hyposensitive hypothalamic-pituitary-adrenal axis following acute restraint stress. These findings are interesting in a number of ways. It showed that our stress models propose to be useful in elucidating the complex interrelationship between an external event or stressor, and the organism experiencing it. Simultaneously it presents a promising platform for the finding of new or better treatments for patients.