Reactive changes in astrocytes, and delayed neuronal death, in the rat hippocampal CA1 region following cerebral ischemia/reperfusion

BACKGROUND： Blood supply to the hippocampus is not provided by the middle cerebral artery. However, previous studies have shown that delayed neuronal death in the hippocampus may occur following focal cerebral ischemia induced by middle cerebral artery occlusion. OBJECTIVE： To observe the relationship between reactive changes in hippocampal astrocytes and delayed neuronal death in the hippocampal CA1 region following middle cerebral artery occlusion. DESIGN, TIME AND SETTING： The immunohistochemical, randomized, controlled animal study was performed at the Laboratory of Department of Neurology, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, from July to November 2007. MATERIALS： Rabbit anti-glial fibrillary acidic protein （GFAP） （Neomarkers, USA）, goat anti-rabbit IgG （Sigma, USA） and ApoAlert apoptosis detection kit （Biosciences Clontech, USA） were used in this study. METHODS： A total of 42 healthy adult male Wistar rats, aged 3–5 months, were randomly divided into a sham operation group （n = 6） and a cerebral ischemia/reperfusion group （n = 36）. In the cerebral ischemia/reperfusion group, cerebral ischemia/reperfusion models were created by middle cerebral artery occlusion. In the sham operation group, the thread was only inserted into the initial region of the internal carotid artery, and middle cerebral artery occlusion was not induced. Rats in the cerebral ischemia/reperfusion group were assigned to a delayed neuronal death （＋） subgroup and a delayed neuronal death （–） subgroup, according to the occurrence of delayed neuronal death in the ischemic side of the hippocampal CA1 region following cerebral ischemia. MAIN OUTCOME MEASURES： Delayed neuronal death in the hippocampal CA1 region was measured by Nissl staining. GFAP expression and delayed neuronal death changes were measured in the rat hippocampal CA1 region at the ischemic hemisphere by double staining for GFAP and TUNEL. RESULTS： After 3 days of ischemia/reperfusion, astrocytes with abnormal morphology were detected in the rat hippocampal CA1 region in the delayed neuronal death （＋） subgroup. No significant difference in GFAP expression was found in the rat hippocampal CA1 region at the ischemic hemisphere in the sham operation group, delayed neuronal death （＋） subgroup and delayed neuronal death （–） subgroup （P 〉 0.05）. After 7 days of ischemia/reperfusion, many GFAP-positive cells, which possessed a large cell body and an increased number of processes, were activated in the rat hippocampal CA1 region at the ischemic hemisphere. GFAP expression in the hippocampal CA1 region was greater in the delayed neuronal death （＋） subgroup and delayed neuronal death （–） subgroup compared with the sham operation group （P 〈 0.01）. Moreover, GFAP expression was significantly greater in the delayed neuronal death （–） subgroup than in the delayed neuronal death （＋） subgroup （P 〈 0.01）. After 30 days of ischemia/reperfusion, GFAP-positive cells were present in scar-like structures in the rat hippocampal CA1 region at the ischemic hemisphere. GFAP expression was significantly greater in the delayed neuronal death （＋） subgroup and delayed neuronal death （–） subgroup compared with the sham operation group （P 〈 0.05）. GFAP expression was significantly lower in the delayed neuronal death （–） subgroup than in the delayed neuronal death （＋） subgroup （P 〈 0.05）. The delayed neuronal death rates were 42% （5/12）, 33% （4/12） and 33% （4/12） at 3, 7 and 30 days, respectively, followingischemia/reperfusion. No significant differences were detected at various time points （χ2 = 0.341, P 〉 0.05）. CONCLUSION： The activation of astrocytes was poor in the hippocampal CA1 region during the early stages of ischemia, which is an important reason for delayed neuronal death. Glial scar formation aggravated delayed neuronal death during the advanced ischemic stage.

Delayed hippocampal neuronal death in young gerbil following transient global cerebral ischemia is related to higher and longer-term expression of p63 in the ischemic hippocampus

The tumor suppressor p63 is one of p53 family members and plays a vital role as a regulator of neuronal apoptosis in the development of the nervous system. However, the role of p63 in mature neuronal death has not been addressed yet. In this study, we first compared ischemia-induced effects on p63 expression in the hippocampal regions （CA1-3） between the young and adult gerbils subjected to 5 minutes of transient global cerebral ischemia. Neuronal death in the hippocampal CA1 region of young gerbils was significantly slow compared with that in the adult gerbils after transient global cerebral ischemia, p63 immunoreactivity in the hippocampal CA1 pyramidal neurons in the sham-operated young group was significantly low compared with that in the sham-operated adult group, p63 immunoreactivity was apparently changed in ischemic hippocampal CA1 pyramidal neurons in both ischemia-operated young and adult groups. In the ischemia-operated adult groups, p63 immunoreactivity in the hippocampal CA1 pyramidal neurons was significantly decreased at 4 days post-ischemia; however, p63 immunoreactivity in the ischemia-operated young group was significantly higher than that in the ischemia-operated adult group. At 7 days post-ischemia, p63 immunoreactivity was decreased in the hippocampal CA1 pyramidal neurons in both ischemia-operated young and adult groups. Change patterns of p63 level in the hippocampal CA1 region of adult and young gerbils after ischemic damage were similar to those observed in the immunohistochemical results. These findings indicate that higher and longer-term expression of p63 in the hippocampal CA1 region of the young gerbils after ischemia/reperfusion may be related to more delayed neuronal death compared to that in the adults.

Neuroprotection of Chrysanthemum indicum Linne against cerebral ischemia/reperfusion injury by anti-inflammatory effect in gerbils

In this study, we tried to verify the neuroprotective effect of Chrysanthemum indicum Linne（CIL） extract, which has been used as a botanical drug in East Asia, against ischemic damage and to explore the underlying mechanism involving the anti-inflammatory approach. A gerbil was given CIL extract for 7 consecutive days followed by bilateral carotid artery occlusion to make a cerebral ischemia/reperfusion model. Then, we found that CIL extracts protected pyramidal neurons in the hippocampal CA1 region（CA1） from ischemic damage using neuronal nucleus immunohistochemistry and Fluoro-Jade B histofluorescence. Accordingly, interleukin-13 immunoreactivities in the CA1 pyramidal neurons of CIL-pretreated animals were maintained or increased after cerebral ischemia/reperfusion. These findings indicate that the pre-treatment of CIL can attenuate neuronal damage/death in the brain after cerebral ischemia/reperfusion via an anti-inflammatory approach.

Effect of hyperthermia on calbindin-D 28k immunoreactivity in the hippocampal formation following transient global cerebral ischemia in gerbils

Calbindin D-28K （CB）, a Ca2＋-binding protein, maintains Ca2＋ homeostasis and protects neurons against various insults. Hyperthermia can exacerbate brain damage produced by ischemic insults. However, little is reported about the role of CB in the brain under hyperthermic condition during ischemic insults. We inves- tigated the effects of transient global cerebral ischemia on CB immunoreactivity as well as neuronal damage in the hippocampal formation under hyperthermic condition using immunohistochemistry for neuronal nuclei （NeuN） and CB, and Fluoro-Jade B histofluorescence staining in gerbils. Hyperthermia （39.5 ＋ 0.2~C） was induced for 30 minutes before and during transient ischemia. Hyperthermic ischemia resulted in neu- ronal damage/death in the pyramidal layer of CA1-3 area and in the polymorphic layer of the dentate gyrus at 1, 2, 5 days after ischemia. In addition, hyperthermic ischemia significantly decreaced CB immunoreac- tivity in damaged or dying neurons at 1, 2, 5 days after ischemia. In brief, hyperthermic condition produced more extensive and severer neuronal damage/death, and reduced CB immunoreactivity in the hippocampus following transient global cerebral ischemia. Present findings indicate that the degree of reduced CB immu- noreactivity might be related with various neuronal damage/death overtime and corresponding areas after ischemic insults.

Protein aggregation in association with delayed neuronal death in rat model of brain ischemia

To investigate the relationship between protein aggregation and delayed neuronal death,we adopted rat models of 20 min ischemia.Brain ischemia was produced using the 2-vessel occlusion(2VO)model in rats Light microscopy,transmission electronic microscopy and Western blot analysis were performed for morphological analysis of neurons,and protein detection.The results showed delayed neuronal death took place at 72 h after ischemia-reperfusion,protein aggregates formed at 4 h after reperfusion and reached the peak at 24 h after reper-fusion,and Western blot analysis was consistent with transmission electronic microscopy.We conclude that protein aggregation is one of the important factors leading to delayed neuronal death.