Effect of insulin-like growth factor and its receptor on the neurologic deficit in rats with cerebral ischemia/reperfusion injury

Feng SUN; Xiaojie DING; Chao WANG; Yunliang GUO

ABSTRACT

BACKGROUND:

It has been demonstrated that insulin-like growth factor-1 (IGF-1) is a kind of neurotrophic factor and protects from cerebral ischemia/reperfusion injury, the expression of IGF-1 is associated with the attack of ischemic stroke. The effects of IGF-1 and its receptor (IGF-1R) on neurobehavioral function are to be further studied.

OBJECTIVE:

To observe the effects of IGF-1 and IGF-1R on neurobehavioral function in rat models of cerebral ischemia/reperfusion injury.

DESIGN:

A randomized controlled observation.

SETTING:

Institute of Cerebrovascular Diseases, Affiliated Hospital of Qingdao University Medical College.MATERIALS The experiments were carried out in Shandong Key Laboratory for Prevention and Treatment of Brain diseases. Twenty-eight healthy adult Wistar rats of clean degree, weighing 220-260 g, were provided by the experimental animal center of Shandong University.

METHODS:

The rats were randomly divided into experimental group (n =24) and sham-operated group (n =4). The middle cerebral artery occlusion/reperfusion (MCAO/R) models were established by inserting a thread through left external-internal carotid arteries. The sham-operated rats were given the same treatments except inserting thread. ①Neurologic deficit test The rats in the experimental group were assessed according to Bederson standard after 1-hour ischemia and 6, 12-hour, 1, 3, 7 and 14-day reperfusion respectively. The sham-operated rats were assessed at corresponding time points; Without neurologic deficit was marked as 0 point; flexion of anterior claws as 1 point; unable to act against the pushing from the contralateral side as 2 points; circling while walking as 3 points; shaking as 4 points;unconscious mind as 5 points. ② Sample collection and treatment The samples in the experimental group were collected after 1-hour ischemia and 6, 12-hour, 1, 3, 7 and 14-day reperfusion, and those in the sham-operated group ere collected at 24 hours postoperatively. The rats were anesthetized, brain samples were got at about 5 mm posterior to optic chiasma after brains were removed completely, then serial coronal sections (5 μm) were prepared, and 1 from 10 sections was stuck to the cover glasses treated with poly-L-lysine. ③ Morphological observation of neurons The neurons in brain were observed by toluidine blue staining. ④ Detection of IGF-1 and IGF-1R The expressions of IGF-1 and IGF-1R in cortex and striatum were detected with immunohistochemical technique, 4 fields were randomly selected to count the positive cells under high-power microscope (×400).MAIN OUTCOME

MEASURES:

① The neurologic deficit; ② Morphological changes of neurons in brain; ③ Expressions of IGF-1 and IGF-1R in cortex and striatum.

RESULTS:

All the 28 rats were involved in the analysis of results. ① The neurologic deficit The scores of neurologic deficit were (1.50±058) and (1.50±0.78) in rats after 7 and 14-day reperfusion, which were lower than that in rats after 6-hour reperfusion [(3.00±0.00), P ＜ 0.05]. ② Morphological changes of neurons in brain The neurons in ischemic area appeared as paryopyknosis and became irregular in shape, there were obvious gaps around the cells, also deeply stained as purplish blue, nucleolus disappeared, and there were many scattered cellular fragments. ③ Expressions of IGF-1 and IGF-1R in cortex and striatum The numbers of IGF-1 positive cells in cortex were (8.75±2.06), (11.13±1.14),(19.75±3.18), (17.38±3.11 ) and (11.23±2.28) respectively in rats after 6, 12-hours and 1, 3, 7-day reperfusion, which all were higher than that in sham-operated rats [(3.88±1.46), P ＜ 0.05], the numbers of IGF-1 positive cells in striatum were(8.25±2.21), (11.34±2.21), (18.23±2.64), (18.56±2.34) and (11.31±2.14) respectively in rats after 6, 12 hours and 1, 3, 7days reperfusion , which were also higher than that in sham-operated rats [(4.12±2.24), P ＜ 0.05]. The numbers of IGF-1R positive cells in cortex were (7.63±1.50), (10.50±2.34), (15.55±3.12), (15.37±3.01), (8.86±2.75) respectively in rats after 6, 12-hours and 1,3,7-day reperfusion, which all were higher than that in sham-operated rats [(4.13±1.81), P ＜0.05]. Those in striatum were (8.33±2.31), (10.24±2.09), (14.72±2.17), (14.24±2.77), (8.38±2.05), which were also higher than that in sham-operated rats [(3.76±2.35), P ＜ 0.05].

CONCLUSION:

The neurological function is damaged after cerebral ischemia/reperfusion, but it has a trend of self-recovery. The expressions of IGF-1 and IGF-1R are mainly distributed in cortex and striatum. Higher expressions of IGF-1 and IGF-1R maintain during 12 hours to 7 days after reperfusion and have a peak value at 1-3 days, which suggests that early expression of IGF-1 and IGF-1R are certain related to the recovery of neurological function.