62 June 2012 Stress and stressors: The role of heat shock proteins Debtanu Barman*1, Vikash Kumar2, Sagar C. Mandal3, Suvra Roy2 and Kundan Kumar2 The increasing contamination of freshwater and marine ecosystems around the world by anthropogenic substances is one category of environmental stressor. Various stressors— such as grading, transportation and vaccination—are necessary components of modern intensive fish culture. The response of the fish to such stressors involves a hierarchy of organization from cell to individual organism to population. Stress is most often associated with a negative perspective. This is natural inasmuch as the word and concept in common use is generally associated with a system that is severely challenged. The stress response is an important normal response of all living organisms. Spanning the range from the induction of certain genes and proteins to a complex behavioral response, the stress response allows organisms to avoid or cope with challenges to homeostasis. This underscores the importance of clarity and precision in defining this important response. Stress is defined here as the response of a cell or organism to any demand placed on it that causes an extension of physiological state beyond the normal resting state. Stress is the sum of the physiological responses by which an animal tries to maintain or establish a normal metabolism, in the face of physical or chemical assaults. The factors that cause stress, as a group, are called stressors. Therefore, a stressor is a causative factor and stress is the response.Rearing aquatic organisms in artificial environments results in exposure to numerous stressors that are often not experienced at the same intensity in natural environments. The stress response of fish follows the general vertebrate pattern. A key element in the stress response is a switch from anabolism to catabolism. The magnitude of the response may vary with the nature of stress and its duration. It also depends on age, sex, maturation stages, species and strain of fish. At the animal level, a series of physiological changes occur following stress challenges that are adaptive in nature. These physiological responses are collectively termed the general adaptation syndrome. The sequential response consists of an alarm reaction when stress hormones are released, a stage of resistance when adaptation occurs and a stage of exhaustion when adaptation is lost because the stress was too severe or long lasting. Classification of the Stress Response A stress response can be classified as primary, including neural and neuroendocrine response; secondary, such as physiological consequence of such primary response; and tertiary, such as changes in behavior, growth rate, increased susceptibility to diseases and change in population. Primary Stress Response This is characterized by the release of adrinocorticotropic hormones (ACTH) from the adenohypophysis and the release of stress hormones, including catecholamines, such as adrenalin, nor-adrenalin and dopamine, and corticosteroids, especially cortisol from the head kidney. In fishes, an adverse condition stimulates the afferent neural pathway that runs in the sympathetic nervous system from the hypothalamus to the chromaffin tissue of the head kidney and stimulates the chromaffin tissue. This leads to the release of catecholamines, which is extremely rapid compared to the release of cortisol. Corticotropin releasing hormone (CRH) or factor (CRF), released from the hypothalamus in the brain, stimulates corticotropic cells of the anterior pituitary (adenohypophysis) to secrete adrenocorticotropic hormone (ACTH). ACTH, in turn, stimulates internal cells to synthesise and release corticosteroids, particularly cortisol, which is the main corticosteroid in fish. Secondary Stress Response In teleost fish, cortisol enters the liver cells where it binds to a nuclear receptor, resulting in activation of genes that produce a series of enzymes with a range of metabolic effects. This results in a suite of biochemical and physiological changes that include hyperglycaemia, hyperlacticaemia, depletion of tissue glycogen reserves, lipolysis and inhibition of protein synthesis. Production of glucose during stress assists the animals in coping with the energy requirement. The stress hormones, adrenalin and cortisol, increase plasma glucose production in fish by gluconeogenesis and glycogenolysis. Catecholamine has a marked influence on cardiovascular functions, leading to changes in blood circulation, gill perfusion and the oxygen carrying capacity of blood. Corticosteroids, on the other hand, stimulate the iontransport mechanism in the gill and kidney. Intracellular stress response is characterized by production of a family of proteins known as heat shock proteins (Hsp).
RkJQdWJsaXNoZXIy MjExNDY=