الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The brain is remarkably responsive to its interactions with the environment, and its morphology is altered by experience in measurable ways. The concept that the brain is the central organ of stress, with downward influences on many physiological processes involved in adaptation, provides a basis for understanding how interventions that are integrative can have enormous preventative and therapeutic benefits by targeting a person’s interpersonal relationships and lifestyle. Other interventions can alter the social environment through policies of the government and private sector that provide groups of individuals with access to and control over environmental, social, and material resources that are important for health and well-being. Stress exposure induces the activation of many different hormonal and neurotransmitter systems.
The effects of chronic stress on cognition are complex. In humans and animals, chronic stress exposure is associated generally with impaired performance in learning and memory tasks. Previous studies found that adults exposed to chronic life stress, either related to social economic class or mental illness, demonstrate decreases in cognitive functions, such as performance on memory tasks. Likewise, rodents that experience repeated stress show deficits on tasks assessing learning or memory.
The hippocampus and the amygdala are essential components of the neural circuitry mediating stress responses. The hippocampus, which provides negative feedback regulation of the stress response, is particularly vulnerable to degenerative changes caused by chronic stress. Hippocampus is a target brain part glococorticoids. Unlike the hippocampus, relatively little is known about how stress affects the amygdale and the nature of its role in the stress response. the amygdala has unique features of structural and functional plasticity that make it especially relevant to our understanding of memory of emotionally arousing and fearful experiences, but also of the pathological consequences of chronic and severe stress.
As rats are nocturnal ie; the dark period is the active period for rats. Previous work has provided clear evidence that chronic phase shifts of the light/dark (LD) cycle interfere with memory. Furthermore, it has long been observed that social isolation is deleterious for rats and that so called ‘isolation stress’ alters physiological and behavioural characteristics. Hence, we examined the effects of two different models of chronic stress on hippocampal and amygdaloid neuronal morphology in rats.
Accordingly, we use darkness and social isolation as type of social environmental stress. 36 Sprague-Dawley rats from both sexes aged 6-7 weeks at the beginning of current study. Each sex had the same experimental condition, undergoes the same experimental procedures and was randomly divided into three groups: A, B, and C containing each 6 rats. group (A) containing socially isolated animal, group (B) contain societal animal and group (C) is the control group. Animal groups learned the first platform position in SE quadrate before applying stress protocol and they learn the second position of platform ant the second week of stress. Both sexes of Societal and isolated rat groups were exposure to daily disrupted light/ dark cycle (6 h light/ 18 h dark) for 28 day. Body weight were recorded daily for each group and MWM test were applied for rat groups at the end
of each week through the 4 week stress. At the end of the 4th week of stress, animals were sacrificed using using ketamine–xylazine as an anesthesia then fresh brain rapid Golgi cox for neuronal staining and study morphological changes. The histomorphometric analysis was performed using the image processing and analysis software (Image J), version 1.49
with 32-bit Java 1.6.0_24. Statistical analysis was employed using Kruskal Wallis test followed by Mann Whitney test if significant results were recorded.
Results obtained during the course of the present study were summarized as follows:
Isolated female rate showing:
• Non significant increase in body weight through 1st, 2nd and 3rd week stress, while the significant increase in body weight appear at the end of 4th week.
• Non significant effect of stress on total time spent in SE quadrate at the end of 1st stress week, while the significant decrease in total time spend in SE quadrate appear at 2nd week and the highly significant showed at the end of 3rd and 4th week in comparing to control female rats.
• Non significant decrease in number of times traveled by rats to SE quadrate at the end of week1 and 2 compared to control. While there was significant decrease at the end of week 3and highly significance decrease ant the end of 4 week compared to control male rats.
• Significant decrease in total time spent by rats in NW quadrate at the end of 2nd week of stress and a highly significant decrease at the end of 4th week, while there was a non significant decrease at the 3rd week of stress compared to female control rats.
• Non significant decrease in number of times traveled by rats to NW quadrate at the end of week 2 and 3 while there was a highly significant decrease at the end of week 4 compared to control female rat.
• Non significant effect of stress on total number of neurons in hippocampus.