Glyprotein components Of Myelin Protein in Experimental Models of Stress -INTRODUCTION



INTRODUCTION:
    
Stress is any uncomfortable “emotional experience accompanied by predictable biochemical, physiological and behavioural changes” (Baum, 1990).  In 1974 Hans Seyle defined stress as ‘‘the non-specific response of the body to any demand imposed upon it” (Selye, 1974). This definition of stress was later modified in 1992 by Chrousos and Gold and the term ‘‘non-specific” replaced by the hypothesis that above a threshold intensity any stressor would elicit the ‘‘stress syndrome” (Chrousos and Gold, 1992).
            
Stress is a complicated physiological mechanism that occurs when there is a real or perceived threat to homeostasis. While it is generally accepted that these processes are adaptive, designed to re-establish homeostasis and allow coping, it is also apparent that inadequate or excessive or prolonged activation of stress systems can disturb normal physiological and behavioural function. This can result in a range of adverse consequences such as depression, impaired cognition, cardiovascular disease, impaired immune function with increased vulnerability to disease, impaired growth and reproductive function, osteoporosis, diabetes, dementia and reduced life expectancy (Charmandari et al., 2005; Tilbrook et al., 2002; Turner 2005).

DEFINITION:
   
A widely accepted definition of stress has been provided by McEwen: ‘‘Stress may be defined as a real or interpreted threat to the physiological or psychological integrity of an individual that results in physiological and/or behavioural responses’’. Stress can affect people of all ages, genders, circumstances and can lead to both physical and psychological health issues (McEwen, 2000).

The stress response is subserved by a complex neuroendocrine, cellular and molecular infrastructure and the stress system is located in both the central and peripheral nervous system. The adaptive response of an individual to stress is determined by a multiplicity of genetic, environmental and developmental factors. Alterations of the ability to respond to stressors may lead to disease.

Some stress can be beneficial at times, producing a boost that provides the drive and energy to help people get through situations like exams or work deadlines. However, an extreme amount of stress can have health consequences and adversely affect the immune, cardiovascular, neuroendocrine and central nervous systems (Anderson, 1998).

In addition, an extreme amount of stress can take a severe emotional toll. While people can overcome minor episodes of stress by tapping into their body’s natural defences to adapt to changing situations, excessive chronic stress, which is constant and persists over an extended period of time, can be psychologically and physically debilitating. Unlike everyday stressors, which can be managed with healthy stress management behaviours, untreated chronic stress can result in serious health conditions including anxiety, insomnia, muscle pain, high blood pressure and a weakened immune system (Baum and Polsusnzy, 1999).  

Research shows that stress can contribute to the development of major illnesses, such as heart disease, depression and obesity. People who suffer from depression and anxiety are at a heightened risk for heart disease, with depression leading to a two-fold increased risk and anxiety a doubling of increased risk (Anderson and Anderson, 2003).  

TYPES OF STRESS RESPONSE:

Stress responses include activation of a va­riety of hormone and neurochemical systems throughout the body. Two hormonal systems have received extensive attention in this regard:
(1) The sympathetic-adrenomedullary (SAM) system, which produces adrenaline in the central part of the adrenal gland, and
(2) The hypotha­lamic-pituitary-adrenocortical (HPA) system, which produces cortisol in the outer shell of the adrenal gland (Sapolsky et al., 2000).

 


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