Hippocampal Neuronal Lesion Of Rats Following Predator Stress And Regulatory Role Of Steroid Receptor System In Hippocampus On The Psychological Stress Responses

Introduction: Stress may cause a series of neuroendocwnal and behavioral changes, including high glucocorticoids (GCs) level and anxiety-like behavior. Reasonable stress responses, such as fighting and defensive behaviore and increase of GCs secretion in endocrine, are vital for individual survival in bad situation. Many studies have demonstrated that stress may result in brain damage, especially hippocampal damage. One of the most important brain areas that mediates, and in turn is affected by, stress responses is the hippocampus. The hippocampus plays an important role in new information learning and memory. This function is critical to the stress responses, for example in assessing potential threat during a life-threatening situation, as occured with exposure to a predator. Individual may be adaptive or mal-adaptive, even down with an illness following stress. Individual mal-adaptation or disorder suffering is consistent with lesion of hippocampal neurons such as nonreversible neuron atrophy and permanent cell loss. Moreover, the magnitude of hippocampal damage is increased with the intensity and duration of stress, which ranges from reversible atrophy of dendrites and neurons to apoptosis or permanent cell loss. Many studies in a variety of animal species and follow-up studies have demonstrated that hippocampal damage was associated with direct excessive exposure of GCs to the hippocampal region. The activation and termination of hypothalamic-pituitary-adrenal axis (HPA) functioning, plays an important role in regulating stress responses and maintaining homeostasis. Thehippocampus has a rich concentration of receptors for GCs, mineralocorticoid receptor (MR) and glucocorticoid receptor (GR). This binary system of receptors in the hippocampus, modulates GCs release through inhibitory effects on HPA. Psychological stress, clearly is different from physical stress in nature. Both have distinct neural pathway from perception of stressor to stress responses. The magnitude of stress responses depends on individual conception and assessing of psychological stressor. Many clinical studies also have suggested that pathogenesis in posttraumatic stress disorder (PTSD), depression, psychophysiological disorders are related to psychological strain or stress. So the research on psychological stress will be helpful for Clarification of the pathogenesis of stress related disorders, strategy of prevention and treatment, and understanding of stress inducing mental injury in forensic psychiatry. A great variety of stressors have been used in research aimed at description and analysis of behavioral and physiological components of the stress response, but the study on psychological stress, so far still depends on ideal animal models. Predators co-existence may provide a series of species relevant aversive stimuli for study the stress response of another species animals and may have some benefits over currently applied stress models. The use of cat exposure to rat in stress research has increased substantially in recent years. Exposure to a potential attacking predator provides a painless stressor, with minimal disturbance to animal or alternation of physical component, better simulates mankind's mental strain and stress in the real-life situation. The present study will investigate the effects of different mode of cat exposure stress on the behavior and endocrine aspect (profile) of rats, hippocampal damage and its nature in neuropathology, and regulating mechanism of steriods receptors on psychological stress responses.Materials and Methods: The psychological stress paradigm is as follow: A cat was used as predator stimulus. The cat-exposure stress test was carried out once a day. Four groups of rats were randomly divided: (1) Rats exposed to a cat only one time (Acute stress); and (2) Rats exposed to a cat daily for 14 consecutive days (2-week consistent stress); and (3) Rats exposed to a cat daily for 28consecutive days (4-week consistent stress); and (4) Rats without cat-exposure (control). Behaviors (staying...