Effect Of Mild Hypothermia Therapy On HSP Expression After Ischemic Brain Damage

Objective: To establish the middle cerebral artery occlusion model by suture occlusion and elevate the reliability of experiment finding.Cerebral infarction is necrosis and softening of brain tissue because the blood disorder cause ischemic and oxygen deficiency. The infarction lesion is made up of central necrosis and peripheral penumbra . Brain cell death because the cerebral blood flow of the central necrosis is seriously or completely deficient, but there are branch circulation in the peripheral penumbra and the cell can get blood supply , the function of neuron is damaged but the neuron is also alive in short period and in an reversible situation , cerebral metabolic block can revive and neuron can survive and restore function if they get blood supply promptly . Heat shock protein is a kind of stress protein produced under pathological condition.Environmental factor and stress stimulus such as ischemia , hypoxia, viral infection, heavy metalion , DNA damage and heat can make it produced . Heat shock protein can protect neuron from stress injury, and is mainly expressed in peripheral penumbra of infarction lesion. By evaluating the quantity of heat shock protein expression , we can assess the size of peripheral penumbra after brain injury so as to explore how to reduce the size of peripheral penumbra after acute cerebrovascular disease , elevate therapy level for cerebrovascular disease , cut down mutilation rate and lethality. Hypothermy is generally divided into mild hypothermia (33~35℃) ; moderate hypothermia(28~32℃) ; profound hypothermia (17~27℃) ; ultraprofound hypothermia(2~16℃). Mild hypothermia is often refered as 32~35℃. Experiment find that administration of mild hypothermia therapy before, during and after ischemia can obviously alleviate pathological injury, promote the revival of neural function after cerebral ischemia.Methods: 48 healthy SD rats, weighing 300—330g, were randomly divided into mild hypothermia group and normal temperature group. Each group was further classified into 12 hours, 24 hours, and 48 hours subgroups. After anesthetized by injecting 10% Chloral Hydrate intrapentoneally , mild hypothermia group pillowed on ice bag were operated when temporalis temperature lower than 35℃,and hold the temperature between 35℃-32℃for two hours . Normal temperature group did not pillow on ice bag. Make a median incision of cervical part, cut the fascia superficialis inter the two glandula angularis to expose sternomastoid muscle of one side . Dissect spatium intermusculare between sternomastoid muscle and sternohyoid muscle bluntly so as to expose common carotid artery and vagus nerve. Insert a filament below the common carotid artery, dissect internal carotid artery and external carotid artery bluntly, then burn the superior thyroid artery and occipital artery, the brunches of external carotid artery, by electric coagulator. Liberate external carotid artery about 3-4mm, and put on two filaments below it. Make a slipknot at the proximum and push it to the base of external carotid artery, deligate the distant part of it, and burn it at the distant ligature. Separate internal carotid artery and its branch pterygopalatine artery, occlude internal carotid artery and external carotid artery by two bulldog clamps. Cut a microstomia on the external carotid artery and insert the prepared filament from external carotid artery to common carotid artery, strict the slipknot at the base of external carotid artery ,unclamp the bulldog clamp at the internal carotid artery , draw the external carotid artery down and keep it in the line with internal carotid artery, insert the filament to internal carotid artery from the crotch of common carotid artery . Pay more attention not to insert the filament to pterygopalatine artery mistakely. When the filament reach the skull, strict the slipknot at the base of external carotid artery, unclamp the bulldog clamp on the common carotid artery, and observe whether it is bleeding . Draw out the filament below the common carotid artery .Continuous suture operative incision , keep the animal warm and observe the behavior and symptom after they awake. Selected standard:①the right forelimb adduct and flex when lifted tail.②circle right when crawling (chasing tail phenomenon).③Tumble to right when standing. The rats of every subgroup were killed at 12 hours , 24hours respectively after neuronal function scoring , get the brain sample and measure the size of infarct by TTC dyeing, observe neuron apoptosis by HE staining ,view the expression of HSP by immunohistochemistry .The result was analyzed by t test .Results: The experiment find that the mild hypothermia group rats neuronal function revive obviously quickly and find that the number of apoptosis neurons is obviously reduced compared with normal temperature group rats in pathological section by HE dyeing. After TTC dyeing there was significant difference in the infarction volume between the 24 hours subgroup and the 48 hours subgroup (p<0.05). The heat shock protein is down-regulation in the mild hypothermia group compared with the normal temperature group between the same subgroup(p<0.05).Conclusion: The middle cerebral artery occlusion model of rat by suture occlusion increased the stability and reliability of cerebral ischemia experiment results. After ischemic injury the neuronal function recovered more quickly in mild hypothermia group than in normal temperature group and there were less apoptosis neurons, smaller infarction volume and less heat shock protein expression. This illustrated that mild hypothermia therapy decreased the peripheral penumbra size of cerebral infarction and increased the ability of tolerance to ischemia and hypoxia. In a word, mild hypothermia is an effective method to treat cerebrovascular disease.