الفهرس 
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Abstract
In this study, forty-two adult male albino rats were used and divided into five groups; the control group (18 rats) and four experimental groups (6 rats each); the acute-stressed group (one day stress), the recovered group after acute stress (6days recovery), the chronic-stressed group (6 days stress), and the recovered group after chronic stress (7days recovery). The induction of stress was performed by restraining animals individually in wire stainless mesh restrainers (5×7×12 cm in dimensions) daily for 2 hr/day without food and water during the stress periods. The rats were sacrificed at the assigned times (on 1st, 7th, and 14th days), the blood samples were obtained by left ventricle puncture and stored at -20ᵒc for serum cortisone assessment. The adrenal glands were dissected, weighed immediately then some parts were preserved in 10% buffered formalin and then processed for paraffin sections stained with Hx & E, immune-histochemical staining with anti-Nestin, anti-chromogranine-A, and anti-GFAP antibodies. Other parts were processed for chromaffin reaction staining. Then, the slides were studied using light microscope and image analysis program. There was an increased plasma cortisol level in the acutely and chronically stressed group as compared to the recovered and control groups. Histopathological examination of the adrenal gland of stressed rats and their recovered groups showed degeneration and disorganization of the gland architecture, vaculations of the cortical and medullary cells, pyknotic nuclei, congestion of the blood vessels and hemorrhage between the cells were detected. Then, morphometric studies were done to evaluate the zona fasciculata and medullary thickness. There was a significant increase in the zona fasciculata thickness of the acute and chronic stressed groups compared to the control group. The medullary thickness was significantly increased in the Recovered group after chronic-stress compared to the control group. The microscopic examination of chromaffin reaction stained sections showed increased positive reaction in the stress group more than recovered and control groups. The immune-histochemical studies showed that appearance of immune-stained Nestin and chromogranine-A positive cells in the adrenal gland of the stressed groups more than the recovered and control groups. However, it was decreased in the case of GFAP immune stain. That may indicate the increase of Nestin progenitor cells at the adrenal gland of the rats exposed to acute stress and the ability of these cells to differentiate into chromaffin cell on exposure to stress, but when stress becomes chronic Nestin positive cells decreased indicates their differentiation into new chromaffin cells for adaptation to stress. Finally, data were subjected to statistical analysis.