Protective effects of astragalus root on hippocampal nerves and learning and memory ability of newborn rats after anoxic-ischemic brain injury / 中国组织工程研究

ABSTRACT

BACKGROUND: Astragalus root can inhibit apoptosis through reducing the release and interstitial accumulation of excitatory amino acids, alleviating calcium overloading and antioxidative effect.OBJECTIVE: Astragalus root was used to treat anoxic-ischemic brain injury in immature brain. We evaluated the effect of astragalus root on caspase-3 mRNA expression, and meanwhile, labyrinth test was employed to investigate the intervention of astragalus root on learning and memory function of mature rats after anoxic-ischemic brain injury.DESIGN: Randomized and controlled study.SETTING: Pediatric Department, Zhongda Hospital Affiliated to the Medical College of Southeast University; Pathological Department, the Basic Medical Sciences Institute of Southeast University.MATERIALS: From October 2002 to June 2003, this study was conducted at the Experiment Center of the Medical College, Southeast University.A batch of 114 seven-day-old SD rats were selected from the same brood and divided into 3 groups, namely, sham-operation group (n=18), model group (n=48) and astragalus root group (n=48). Astragalus injection was produced by Chengdu DIAO Pharmaceutical Factory, with 10 mL astragalus injection corresponding to 20 g raw material.METHODS: Animal model of anoxic-ischemic brain injury was established in model group and astragalus root group, but was not established in sham-operation group. In astragalus root group, immediately after establishing anoxic-ischemic model and at the same time point each day, 0.08 mL astragalus injection was administered intraperitoneally until the 7th postoperative day. In model group, 0.08 mL normal saline was administered at the same time points. In sham-operation group, no treatment was given. In astragalus root group and model group, animals were decollatedat 24 hours and 5 days postoperatively to take out the brains. In sham-operation group,animals were decollated and their brains were taken out at 24 hours postoperatively. In all the groups, hippocampal brain injury was detected using histopathological method combined with semi-quantified RT-PCR methods for detecting caspase-3 mRNA. Adult rats aged 90 days were used in modified y maze to examine their learning and memory functions. All these three experiments were independent.MAIN OUTCOME MEASURES:① Hippocampal brain injury in each group was evaluated using pathological method.② Caspase-3 mRNA in the ligated side of hippocampus was detected.③ Results of modified Y maze test were analyzed.RESULTS:All of the 114 rats entered the statistical analysis.① Assessment ofhippocampal brain injury in each group with pathological method:In sham-operation group, the bilateral hippocampus showed no swelling or necrosis, and neural cells in this area had normal morphological features with a density of (87.7±0.6) × 103 per high amplification field. In model group, the ligated side of hippocampus was swollen with a widened spatium and the cell density decreased to (68.8±3.0) × 103 per high amplification field, which significantly differed from that in sham-operation group (P ＜ 0.01). At the fifth day, the volume of ligated side of hippocampus reduced with pyramid layer disorganized and neural cells sparse at a density of (48.7±2.2) × 103 per high amplification field. These changes were significantly different from those of sham-operation group and the same side at 24 hours (P ＜ 0.01). At 24 hours the ligated side of hippocampus was less swollen in astragalus root group than in model group.At day 5, the whole hippocampus was observed. At these two time points,cell death rate in astragalus root group was significant lower than that in model group(P ＜ 0.01).②Caspase-3 mRNA in the ligated side of hippocampus in all the groups: In sham-operation group, the expression of caspase-3 was low, with an absorbency value of 0.220±0.009. In model group, after ischemia and anoxia its expression increased. At 6 hours, it was 11% higher than that in sham-operation group. In astragalus root group, mRNA level reached its peak, which was 260% higher than that in sham-operation group (P ＜ 0.01). The peak of mRNA continued, decreased after 48 hours and returned to baseline at 5 days and 7 days. The fluctuation of mRNA was similar between astragalus root group and model group,but the peak value at 24 hours and 48 hours in astragalus root group was 44％-46％ lower than that in model group (P ＜ 0.01). ③ Results of modified Y maze test: As compared to model group, in astragalus root group, the number of training times for meeting the standard made by the Association was significantly smaller [(45.7±2.7), (16.1±2.5) times, P ＜ 0.01] and at 24 hours after anoxia and ischemia, memory retention was significantly higher [(48.3±11.7), (80.0±9.0)%, P ＜ 0.01].CONCLUSION: Astragalus root can effectively inhibit the apoptosis of neural cells in hippocampus in immature brain after anoxia and ischemia and enhance the survival rate of them. This protective effect may be related to its inhibitory effect on the expression of caspase-3. Meanwhile, astragalus root can dramatically improve learning and memory function of the immature brain after anoxia and ischemia.