| Heat stress is defined as perceived discomfort and physiological strain associated with exposure to a hot environment,especially during physical work.Heat stress causes central nervous system abnormalities such as delirium, convulsions,or coma resulting from exposure to environmental heat or strenuous physical exercise.Heat stress induces thermoregulatory, acute-phase, and heat-shock responses.Heat stress impacts on the character of brain cells,changes the cognitive process, which in turn induce effects on human behavious and quality of life.Hypothalamus is a very important subcortical center which was involved in functions of many aspects,especially in maintaining the balance of organism internal environment. Hypothalamus (eg, preoptic area and anterior hypothalamus area) is a temperature regulating center,heat stress can activate the neurons in hypothalamus. Supraoptic nucleus(SON) and paraventricular ncleus(PVN) are two important nucleus in hypothalamus,which not only participate in integration of balance of water and salt,stabling blood pression et al,but also in regulation of various kinds of stress.Heat stress induced the changes in neurons and glial cells in SON and PVN in hypothalamus of rats are not clear yet.Objective:To observe the expression of Fos protein,TRPV4 protein and GFAP in SON and PNV of rats treated with various high temperature and the effects of heat stress on neurons and glial cells.Method:The adult rats were located within the experimental incubator, the temperature within the incubator was regulated to 24℃,34℃,38.5℃or 42℃respectively and the relatively humidity was 60%, for 60 minutes, and observe the rats'behaviour.Immunohisto- chemical method was used to observe the responses of Fos-positive neurons,TRPV4-positive neurons and GFAP-positive astrocytes in SON and PVN of hypothalamus on heat stress.Anti-Fos single-,anti-GFAP single-, anti-TRPV4 single-, anti-Fos/GFAP-, anti-TRPV4/GFAP- and anti-TRPV4/NeuN- double immunohistochemical method were used.In addition, investigated the expression of TRPV4mRNA in hypothalamus with RT-PCR.Results:The behaviors results showed: At 24℃, behaviour of rats was normal and the rectal temperature was about 36℃;At 34℃,the behavior of rat had no changes, and the rectal temperature raised to 38℃; At 38.5℃and 42℃, the rats depressed at first and then came into emotional state.The immunohistochemical staining result show: ①At 24℃, Fos-positive neurons were rare in SON and PVN; at 34℃,increased;at 38.5℃,peaked;at 42℃,decreased markedly. Three different types of Fos positive cells were found: Fos protein only expressed in the nucleus; Fos protein only appeared within the cytoplasms; Fos protein can be found in both the nucleus and the cytoplasms.②TRPV4 protein revealed in neurons,not in astrocytes.At 24℃,TRPV4-positive neurons were rare in SON and PVN; increased at 34℃; peaked at 38.5℃and decreased significantly at 42℃.③At 24℃, GFAP-positive astrocytes were rare in hypothalamus, At 34℃, GFAP-positive cells increased in many nucleus(AHA,Sch,PVN,Arc,SON)and at 38.5℃peaked while markedly decreased at 42℃.At 42℃, Fos/GFAP double labelled astrocytes were found.④After heat stress the expression of TRPV4mRNA increased.Conclusion:①The hypothalamic SON and PVN participate in regulating heat stress.②After heat stress,Fos can not only be a mark for cellular activity,it can also be a mark for degree of cell injury.③TRPV4 participates in the pathophysiology of heat stress and it may be a kind of molecular mechanism in regulating body temperature.④Except neurons,astrocytes also participate in regulating heat stress.⑤Ambient temperature above 42℃can cause obvious heat injury,to rats, 420C may be the tolerance physiological limit.
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