Repeated cerebral ischemia induced hippocampal cell death and impairments of spatial cognition in the rat

We developed a method of causing strong ischemic insult only in vulnerable nerve cells, such as hippocampal cells, without causing hemiplegia or difficulty in moving, by repeating cerebral ischemia for a brief time with a short interval periods. The rats subjected to 10 min of cerebral ischemia exhibited no impairment of spatial cognition at the test trial 7 days after final reperfusion. However, when the 10 min ischemia was repeated twice with a 1 hr interval, the rats exhibited a significant decrease in number of correct choices and increase in number of errors. Three times of repeated cerebral ischemia also induced a significant decrease in the number of correct choices and increase in the number of errors, but there were some rats showing motor difficulty. Cell death was typically observed in the CA1 layer of the hippocampus of rats subjected twice to 10 min of cerebral ischemia. Hippocampal and cortical acetylcholine (ACh) release weas transiently increased during the first and second 10 minutes of ischemia and normalized immediately after recirculation; thereafter, ACh release from these areas gradually decreased and showed a significantly low level at 7 days after recirculation. These results suggest that the repeated cerebral ischemia-induced impairment of spatial memory may be due to the dysfunction of hippocampal and cortical ACh systems and hippocampal cell death. The repeated cerebral ischemia model which produces cell death and ACh dysfunction in the hippocampus is thought to be useful for evaluating new drugs for the treatment of cerebrovascular dementia.     

Inhibition of poly (ADP-ribose) polymerase and caspase-3, but not caspase-1, prevents apoptosis and improves spatial memory of rats with twice-repeated cerebral ischemia

The effect of inhibition of PARP [(poly (ADP-ribose) polymerase], caspase-3 and caspase-1 on twice-repeated ischemia-induced apoptosis and memory impairment were examined. The twice repeated ischemia was induced by four-vessel occlusion method in which a 10 min ischemic episode was repeated once after 60 min. The spatial memory was assessed using 8-arm radial maze. The results of this study showed that the repeated ischemia impaired memory and induced apoptosis in hippocampus CA1 field after 7 days. Moreover, 3-aminobezamide (10 mg/kg i.v.), a PARP inhibitor, and Ac-DEVD-CHO (8.4 microg/5 microL i.c.v., bilaterally), a caspase-3 inhibitor, decreased apoptosis by 45% and 58% respectively. Both drugs reduced the error choices, but 3-aminobezamide additionally increased the correct choices and improved the memory when either drug was injected immediately after the ischemic insult. The results also showed that inhibition of interleukin-1beta-converting enzyme, ICE (caspase-1) by Z-ASP-DCB-CH2 (100 microg/kg i.c.v., bilaterally) neither decreased apoptosis (13% reduction) nor improved memory of the ischemic rats. These results suggest that direct inhibition of PARP and caspase-3, but not of caspase-1, prevents apoptosis and improves spatial memory impaired by repeated ischemia.     

Acute and chronic estradiol treatments reduce memory deficits induced by transient global ischemia in female rats

Transient global ischemia induces selective, delayed neuronal death in the hippocampal CA1 and delayed cognitive deficits. Estrogen treatment ameliorates hippocampal injury associated with global ischemia. Although much is known about the impact of estrogen on neuronal survival, relatively little is known about its impact on functional outcome assessed behaviorally. We investigated whether long-term estradiol (21-day pellets implanted 14 days prior to ischemia) or acute estradiol (50 μg infused into the lateral ventricles immediately after ischemia) attenuates ischemia-induced cell loss and improves visual and spatial working memory in ovariectomized female rats. Global ischemia significantly impaired visual and spatial memory, assessed by object recognition and object placement tests at 6-9 days. Global ischemia did not affect locomotion, exploration, or anxiety-related behaviors, assessed by an open-field test at 6 days. Long-term estradiol prevented the ischemia-induced deficit in visual working memory, maintaining normal performance in tests with retention intervals of up to 1 h. Long-term estradiol also prevented ischemia-induced deficits in spatial memory tests with short (1 and 7 min), but not longer (15 min), retention intervals. Acute estradiol significantly improved visual memory assessed with short retention intervals, but did not prevent deficits in spatial memory. Acute estradiol significantly increased the number of surviving CA1 neurons, assessed either at 7 days after ischemia or after the completion of behavioral testing 9 days after ischemia. In contrast, chronic estradiol did not reduce CA1 cell death 9 days after ischemia. Thus, long-term estradiol at near physiological levels and acute estradiol administered after ischemic insult improve functional recovery after global ischemia. These findings have important implications for intervention in the neurological sequellae associated with global ischemia.     

Changes in HPA reactivity and noradrenergic functions regulate spatial memory impairments at delayed time intervals following cerebral ischemia

This study investigates the association of ischemia-induced spatial memory impairment to alterations of the HPA axis and noradrenergic activation post insult. Experiment 1 characterized the effects of 10 min forebrain ischemia on corticosterone (CORT) secretion following ischemia and in response to spatial memory assessment in the Barnes maze, as well as the impact of pre-ischemia treatment with the glucocorticoid inhibitor metyrapone (175 mg/kg; s.c.). The results showed that cerebral ischemia represents a significant physiological stressor that upregulated CORT secretion 1, 24 and 72 h post-ischemia but not at 7 days. In response to testing in the Barnes maze ischemic animals showed elevated CORT secretion simultaneously with spatial memory deficits. The single dose of metyrapone attenuated the ischemia-induced adrenocortical hyper-responsiveness and subsequent memory deficits despite not providing neuroprotection in the hippocampal CA1 pyramidal cells. To complement these findings, we examined whether norepinephrine which provides positive feedback to the HPA axis and is upregulated following brain ischemia could influence memory performance at delayed intervals after ischemia. Experiment 2 demonstrated that pre-testing administration of the alpha2-adrenoceptor agonist clonidine (.04 mg/kg, s.c.) attenuated ischemia-induced working memory impairments in a radial maze while opposite effects were obtained with the antagonist yohimbine (.3 mg/kg, s.c.). Post-testing administration of clonidine produced spatial reference memory impairments in ischemic rats. The findings from the current study demonstrate increased sensitization and responsiveness of systems regulating stress hormones at long intervals post ischemia. Importantly, we demonstrate that these effects contribute to post ischemic cognitive impairments which can be attenuated pharmacologically even in the presence of hippocampal degeneration at time of testing.     

Effect of Antioxidant Treatment in Global Ischemia and Ischemic Postconditioning in the Rat Hippocampus

Ischemic postconditioning is a very effective way how to prevent delayed neuronal death. Effect of Ginkgo biloba extract (EGb 761; 40 mg/kg) posttreatment was studied on the rat model of transient forebrain ischemia and ischemia/postconditioning. Global ischemia was produced by four-vessel occlusion in Wistar male rats. Two experimental protocols were used: (a) 10 min of ischemia/7 days of reperfusion with or without EGb 761 treatment or (b) 10 min of ischemia/2 days of reperfusion/5 min of ischemia (postconditioning), following 5 days of reperfusion. EGb 761 was applied as follows: 30 min before 10 min of ischemia then 5 h, 1 and 2 days after 10 min of ischemia. Fluoro Jade B, marker for neuronal degeneration, was used for quantitative analysis of the most vulnerable hippocampal CA1 neurons. Cognitive and memory functions were tested by Morris water maze, as well. Administration of EGb 761 30 min before 10 min of ischemia or 5 h after ischemia has rather no protective effect on neuronal survival in CA1 region. Ten minutes of ischemia following ischemic postconditioning after 2 days of reperfusion trigger a significant neuroprotection of CA1 neurons, but it is abolished by EGb 761 posttreatment. Ischemia/postconditioning group showed a significant improvement of learning and memory on the seventh day of reperfusion. Protection of the most vulnerable CA1 neurons after ischemia/postconditioning is abolished by exogenous antioxidant treatment used in different time intervals after initial ischemia. Moreover, combination of EGb 761 administration with repeated stress (5 min ischemia used as postconditioning) causes cumulative injury of CA1 neurons.     

Evidence for a Role of Second Pathophysiological Stress in Prevention of Delayed Neuronal Death in the Hippocampal CA1 Region

In ischemic tolerance experiment, when we applied 5-min ischemia 2 days before 30-min ischemia, we achieved a remarkable (95.8%) survival of CA1 neurons. However, when we applied 5-min ischemia itself, without following lethal ischemia, we found out 45.8% degeneration of neurons in the CA1. This means that salvage of 40% CA1 neurons from postischemic degeneration was initiated by the second pathophysiological stress. These findings encouraged us to hypothesize that the second pathophysiological stress used 48 h after lethal ischemia can be efficient in prevention of delayed neuronal death. Our results demonstrate that whereas 8 min of lethal ischemia destroys 49.9% of CAI neurons, 10 min of ischemia destroys 71.6% of CA1 neurons, three different techniques of the second pathophysiological stress are able to protect against both: CA1 damage as well as spatial learning/memory dysfunction. Bolus of norepinephrine (3.1 μmol/kg i.p.) used two days after 8 min ischemia saved 94.2%, 6 min ischemia applied 2 days after 10 min ischemia rescued 89.9%, and an injection of 3-nitropropionic acid (20 mg/kg i.p.) applied two days after 10 min ischemia protected 77.5% of CA1 neurons. Thus, the second pathophysiological stress, if applied at a suitable time after lethal ischemia, represents a significant therapeutic window to opportunity for salvaging neurons in the hippocampal CA1 region against delayed neuronal death.     

Dehydroevodiamine.HCl prevents impairment of learning and memory and neuronal loss in rat models of cognitive disturbance

We previously reported that dehydroevodiamine.HCl (DHED) has anticholinesterase and antiamnesic activities. To verify the effects of DHED on cognitive deficits further, we tested it on the scopolamine-induced amnesia model of the rat using the passive avoidance and eight-arm radial maze tests. A single (20 mg/kg p.o.) and repeated (10 mg/kg p.o.) administrations of DHED could significantly reverse the latency time shortened by scopolamine (1 mg/kg i.p.) to control level. The impaired spatial working memory induced by scopolamine (1 mg/kg i.p.) was also improved significantly by a single injection (6.25 mg/kg i.p.) and repeated administrations of DHED (10 mg/kg p.o.) in the eight-arm radial maze test. In addition, we examined the effects of DHED on the memory impairment and the histological changes of the brain after unilateral electrolytic lesion of the entorhinal cortex (EC) and middle cerebral artery occlusion in rats. The cognitive deficits caused by EC lesion and middle cerebral artery occlusion were improved significantly by repeated administrations of DHED (6.25 mg/kg i.p.) after EC lesion or ischemic insult once a day for 7 days in the passive avoidance test. Histological analysis showed that the neuronal loss in the DHED-treated group was notably reduced in the hippocampal area (CA1) of ischemic rats and in the dentate gyrus and hippocampal area (CA1 and CA3) of EC-lesioned rats compared with the nontreated group. The infarction area was decreased significantly by a single administration of DHED (6.25 mg/kg i.p.) 30 min before ischemic insult for 6 h. These results suggest that DHED might be an effective drug for not only the Alzheimer's disease type, but also the vascular type of dementia.     

Thyroxine attenuates hippocampal neuronal damage caused by ischemia in the rat.

We investigated the effect of thyroxine against neuronal damage caused by ischemia in the rat. Neuronal damage was evaluated in the hippocampal CA1 subfield 7 days after a 10 min forebrain ischemia. Thyroxine was administered to animals divided in three groups: 15 min prior to ischemia (group 1), immediately after ischemia (group 2), and both before and after ischemia (group 3). The treatment of rats with a single dose of thyroxine given pre- or postischemia failed to prevent the loss of CA1 pyramidal cells. In contrast, repetitive administration of thyroxine before and after ischemia reduced the damage of the CA1 pyramidal cells. The mechanisms possibly underlying this neuroprotective effect are discussed.     

多巴胺D1和D2受体激动剂和拮抗剂对脑缺血/再灌注损伤的影响

实验应用开阔法、组织病理学方法、原位末端标记(in situ terminal deoxynucleotidyl transferase-metliated de-oxy-UTP mick end labeling,TUNEL)法及免疫组织化学等方法,探讨多巴胺D1、D2受体激动剂和拮抗剂对沙土鼠前脑缺血／再灌注损伤海马CA1区神经元凋亡及凋亡相关基因bcl-2、bax表达的影响。结果显示：前脑缺血5min可引起沙土鼠探索活动增加;再灌注3d,海马CA1区约95％的锥体细胞凋亡;再灌注7d,海马CA1区仅残存约2％—7％的存活锥体细胞;前脑缺血5min可抑制bcl-2的表达并诱导bax表达增高;预先应用D2受体激动剂培高利特可减轻缺血后沙土鼠行为学异常、抑制海马CA1区锥体细胞凋亡、提高锥体细胞存活数、显著诱导bcl-2的表达并抑制bax的表达。预先应用SKF38393、SCH23390及螺哌隆对以上结果无明显影响。实验结果提示,培高利特具有确切的脑保护作用,诱导bcl-2并抑制bax的表达可能是其脑保护作用机制之一。     

Activating Autophagy in Hippocampal Cells Alleviates the Morphine-Induced Memory Impairment

Morphine abuse in treating severe and chronic pain has become a worldwide problem. But, chronic morphine exposure can cause memory impairment with its mechanisms not fully elucidated by past research sstudies which all focused on the harmful effects of morphine. Autophagy is an important pathway for cells to maintain survival. Here we showed that repeated morphine injection into C57BL/6 mice at a dose of 15 mg/kg per day for 7 days activated autophagic flux mainly in the hippocampi, especially in neurons of hippocampal CA1 region and microglia, with spatial memory impairment confirmed by Morris water maze test. Autophagy inhibition by 3-methyladenine obviously aggravates this morphine-induced memory impairment, accompanied with increased cell deaths in stratum pyramidale of hippocampal CA1, CA3, and DG regions and the activation of microglia to induce inflammation in hippocampus, such as upregulated expression of TNF-α, IL-1β, IL-6, and iNOS, as well as NF-κB’ s activation, while morphine alone promoted microglial immunosuppression in hippocampus with autophagy activation which was also confirmed in primary microglia. Taken together, our data indicates that autophagy activating in hippocampal cells can alleviate the memory impairment caused by morphine, by decreasing neuronal deaths in hippocampus and suppressing inflammation in hippocampal microglia, implying that modulating the activation of autophagy might be a promising method to prevent or treat the memory impairment caused by morphine.     

l-3-n-Butylphthalide Activates Akt/mTOR Signaling,Inhibits Neuronal Apoptosis and Autophagy and Improves Cognitive Impairment in Mice with Repeated Cerebral Ischemia–Reperfusion Injury

l-3-n-Butylphthalide (l-NBP) exerts neuroprotective effects in animal models of cerebral ischemia, but its potential benefits in repeated cerebral ischemia–reperfusion (RCIR) injury remain unknown. We investigated the effect of l-NBP on cognitive impairment induced by RCIR in mice. Male C57Bl/6 mice received sham surgery or bilateral common carotid artery occlusion (3 times, 20 min each) and were orally administered preoperative l-NBP (30 mg/kg/day, 7 days), postoperative l-NBP (30 or 60 mg/kg/day, 28 days) or postoperative vehicle (28 days). Learning and memory were assessed by the Morris water maze task and step-down passive avoidance test. Nissl staining was used to identify pathologic changes in the hippocampal CA1 region. The expressions of proteins associated with signaling, apoptosis and autophagy were assessed by quantitative PCR and western blot. RCIR induced deficits in learning and memory that were alleviated by preoperative or postoperative l-NBP administration. Pathologic lesions in the hippocampal CA1 region induced by RCIR were less severe in mice treated with l-NBP. Preoperative or postoperative l-NBP administration in mice receiving RCIR promoted hippocampal expression of phospho-Akt and phospho-mTOR (suggesting activation of Akt/mTOR signaling), increased the Bcl-2/Bax ratio (indicating suppression of apoptosis) and reduced the LC3-II/LC3-I ratio (implying inhibition of autophagy). Preoperative or postoperative l-NBP administration also depressed hippocampal levels of beclin-1 mRNA (indicating suppression of autophagy). These findings suggest that the effect of l-NBP to alleviate learning and memory deficits in mice following RCIR may involve activation of Akt/mTOR signaling and regulation of the expressions of proteins related to apoptosis and autophagy.

     

Neuroprotection by methanol extract of Uncaria rhynchophylla against global cerebral ischemia in rats

In traditional Oriental medicine, Uncaria rhynchophylla has been used to lower blood pressure and to relieve various neurological symptoms. However, scientific evidence related to its effectiveness or precise modes of action has not been available. Thus, in the current study, we evaluated neuroprotective effects of U. rhynchophylla after transient global ischemia using 4-vessel occlusion model in rats. Methanol extract of U. rhynchophylla administered intraperitoneally (100-1000 mg/kg at 0 and 90 min after reperfusion) significantly protected hippocampal CA1 neurons against 10 min transient forebrain ischemia. Measurement of neuronal cell density in CA1 region at 7 days after ischemia by Nissl staining revealed more than 70% protection in U. rhynchophylla-treated rats compared to saline-treated animals. In U. rhynchophylla-treated animals, induction of cyclooxygenase-2 in hippocampus at 24 hr after ischemia was significantly inhibited at both mRNA and protein levels. Furthermore, U. rhynchophylla extract inhibited TNF-alpha and nitric oxide production in BV-2 mouse microglial cells in vitro. These anti-inflammatory actions of U. rhynchophylla extract may contribute to its neuroprotective effects.     

Effect of Cardiac Arrest on Cognitive Impairment and Hippocampal Plasticity in Middle-Aged Rats

Cardiopulmonary arrest is a leading cause of death and disability in the United States that usually occurs in the aged population. Cardiac arrest (CA) induces global ischemia, disrupting global cerebral circulation that results in ischemic brain injury and leads to cognitive impairments in survivors. Ischemia-induced neuronal damage in the hippocampus following CA can result in the impairment of cognitive function including spatial memory. In the present study, we used a model of asphyxial CA (ACA) in nine month old male Fischer 344 rats to investigate cognitive and synaptic deficits following mild global cerebral ischemia. These experiments were performed with the goals of 1) establishing a model of CA in nine month old middle-aged rats; and 2) to test the hypothesis that learning and memory deficits develop following mild global cerebral ischemia in middle-aged rats. To test this hypothesis, spatial memory assays (Barnes circular platform maze and contextual fear conditioning) and field recordings (long-term potentiation and paired-pulse facilitation) were performed. We show that following ACA in nine month old middle-aged rats, there is significant impairment in spatial memory formation, paired-pulse facilitation n dysfunction, and a reduction in the number of non-compromised hippocampal Cornu Ammonis 1 and subiculum neurons. In conclusion, nine month old animals undergoing cardiac arrest have impaired survival, deficits in spatial memory formation, and synaptic dysfunction.     

Delayed Postconditionig Initiates Additive Mechanism Necessary for Survival of Selectively Vulnerable Neurons After Transient Ischemia in Rat Brain

1. The aim of this study was to validate the role of postconditioning, used 2 days after lethal ischemia, for protection of selectively vulnerable brain neurons against delayed neuronal death.2. Eight, 10, or 15 min of transient forebrain ischemia in rat (four-vessel occlusion model) was used as initial lethal ischemia. Fluoro Jade B, the marker of neurodegeneration, and NeuN, a specific neuronal marker were used for visualization of changes 7 or 28 days after ischemia without and with delayed postconditioning.3. Our results confirm that postconditioning if used at right time and with optimal intensity can prevent process of delayed neuronal death. At least three techniques, known as preconditioners, can be used as postconditioning: short ischemia, 3-nitropropionic acid and norepinephrine. A cardinal role for the prevention of death in selectively vulnerable neurons comprises synthesis of proteins during the first 5 h after postconditioning. Ten minutes of ischemia alone is lethal for 70% of pyramidal CA1 neurons in hippocampus. Injection of inhibitor of protein synthesis (Cycloheximide), if administered simultaneously with postconditioning, suppressed beneficial effect of postconditioning and resulted in 50% of CA1 neurons succumbing to neurodegeneration. Although, when Cycloheximide was injected 5 h after postconditioning, this treatment resulted in survival of 90% of CA1 neurons.4. Though postconditioning significantly protects hippocampal CA1 neurons up to 10 min of ischemia, its efficacy at 15 min ischemia is exhausted. However, protective impact of postconditioning in less-sensitive neuronal populations (cortex and striatum) is very good after such a damaging insult like 15 min ischemia. This statement also means that up to 15 min of ischemia, postconditioning does not induce cumulation of injuries produced by the first and the second stress.     

Acute pretreatment with estradiol protects against CA1 cell loss and spatial learning impairments resulting from transient global ischemia

Estradiol can act to protect against hippocampal damage resulting from transient global ischemia, but little is known about the functional consequences of such neuroprotection. The present study examines whether acute estradiol administered prior to the induction of transient global ischemia protects against hippocampal cell death and deficits in performance on a spatial learning task. Ovariectomized female rats were primed with estradiol benzoate or oil vehicle 48 and 24 h prior to experiencing one of three durations of 4-vessel occlusion (0, 5, or 10 min). Performance on the cued and hidden platform versions of the Morris water maze was assessed 1 week following ischemia. On the cued platform task, neither hormone treatment nor ischemia significantly influenced acquisition. When tested on the hidden platform task, however, oil-treated rats exhibited impairments in spatial learning after either 5 or 10 min of ischemia while estradiol-treated rats showed no impairments after 5 min of ischemia and only mild impairments after 10 min of ischemia. Immediately following behavioral testing, rats were perfused and survival of CA1 pyramidal cells was assessed. Ischemia was associated with the loss of CA1 pyramidal cells but rats that received estradiol prior to ischemia showed less severe damage. Furthermore, the extent of cell loss was correlated with degree of spatial bias expressed on a probe trial following hidden platform training. These findings indicate that acute exposure to estradiol prior to ischemia is both neuroprotective and functionally protective.     

Comparison of Glial Activation in the Hippocampal CA1 Region Between The Young and Adult Gerbils After Transient Cerebral Ischemia

It has been reported that young animals are less vulnerable to brain ischemia. In the present study, we compared gliosis in the hippocampal CA1 region of the young gerbil with those in the adult gerbil induced by 5?min of transient cerebral ischemia by immunohistochemistry and western blot for glial cells. We used male gerbils of postnatal month 1 (PM 1) as the young and PM 6 as the adult. Neuronal death in CA1 pyramidal neurons in the adult gerbil occurred at 4?days posti-schemia; the neuronal death in the young gerbil occurred at 7?days post-ischemia. The findings of glial changes in the young gerbil after ischemic damage were distinctively different from those in the adult gerbil. Glial fibrillary acidic protein-immunoreactive astrocytes, ionized calcium-binding adapter molecule (Iba-1), and isolectin B4-immunoreactive microglia in the ischemic CA1 region were activated much later in the young gerbil than in the adult gerbil. In brief, very less gliosis occurred in the hippocampal CA1 region of the young gerbil than in the adult gerbil after transient cerebral ischemia.     

Indomethacin enhances learning and memory potential by interacting with CaMKII

The present study examined the effect of indomethacin (IM), a cyclooxygenase inhibitor, on learning and memory functions. IM activated Ca(2+) /calmodulin-dependent protein kinase II (CaMKII) in cultured rat hippocampal neurons. IM (100 μM) significantly increased the rate of spontaneous AMPA receptor-mediated miniature excitatory postsynaptic currents elicited from CA1 pyramidal neurons of rat hippocampal slices, without affecting the amplitude, and enhanced extracellular high K(+) (20 mM)-induced glutamate release from rat hippocampal slices, indicating that IM stimulates presynaptic glutamate release. Those IM effects were clearly inhibited by the CaMKII inhibitor KN-93. IM persistently facilitated synaptic transmission monitored from the CA1 region of rat hippocampal slices in a concentration (1-100 μM)-dependent manner that was also abolished by KN-93. In the water maze test, IM (1 mg/kg, i.p.) enhanced spatial learning and memory ability for normal rats, and ameliorated scopolamine-induced spatial learning and memory impairment or age-related spatial learning and memory deterioration for senescence-accelerated mouse-prone 8 mice. In the test to learn 15 numbers consisting of three patterns of five digit number for healthy human subjects, oral intake with IM (25 mg/kg) significantly raised the scores of correct number arrangements that subjects memorized 5 min and 3 days after the test. The results of the present study indicate that IM could enhance learning and memory potential by facilitating hippocampal synaptic transmission as a result from stimulating presynaptic glutamate release under the control of CaMKII.     

东莨菪碱慢性给药大鼠作为老龄相关记忆损害模型的探索

目的对东莨菪碱慢性给药大鼠能否作为老龄相关记忆损害模型进行探索。方法14只1月龄SD大鼠随机分为对照组和东莨菪碱模型组。东莨菪碱模型组大鼠皮下注射东莨菪碱2mg kg,2次日,正常对照组予等量生理盐水,连续21d。然后利用Morris水迷宫(MWM)参照记忆试验进行行为学测试;神经元的特殊染色及电子显微镜技术,观察大鼠海马CA1、CA3区锥体细胞数、超微结构的改变以及突触可塑性变化。结果东莨菪碱组大鼠隐匿平台搜索实验成绩有一定损害;两组大鼠空间探索次数差异无显著性(P>0.05)。两组间海马CA1、CA3区锥体细胞数差异无显著性(P>0.05)。两组大鼠锥体细胞胞体超微结构无差异,但两组大鼠CA1区神经元突触超微结构有轻微变化。结论东莨菪碱慢性给药对大鼠学习记忆能力有一定损害,但对长时记忆无明显影响;对海马神经元结构无明显损害,对神经元突触可塑性有轻微影响。此种动物模型可能不是理想的老年性痴呆或老年相关记忆损害模型。     

肢体缺血预处理减少大鼠全脑缺血再灌注诱导的海马CA1区锥体神经元凋亡

探探讨肢体缺血预处理(limb ischemic preconditioning,LIP)对大鼠全脑缺血再灌注后海马CA1区锥体细胞凋亡的影响。46只大鼠椎动脉凝闭后分为假手术组、肢体缺血组、脑缺血组、LIP组。重复夹闭大鼠双侧股动脉3次(每次10min,间隔10min)作为LIP,之后立即夹闭双侧颈总动脉进行全脑缺血8min后再灌注。DNA凝胶电泳、TUNEL和吖啶橙/溴乙锭(AO/EB)双染技术从生化和形态学方面观察海马神经元凋亡的情况。凝胶电泳显示,脑缺血组出现了凋亡特征性DNA梯状条带,而LIP组无上述条带出现。与脑缺血组比较,LIP可明显减少海马CAI区TUNEL阳性神经元数(17.8±5.8vs 69.8±12,P<0.01)。AO/EB染色也显示LIP可明显减少脑缺血再灌注引起的神经元凋亡。以上结果提示,LIP可抑制脑缺血再灌注后海马神经元的凋亡,进而减轻脑缺血再灌注损伤,提供脑保护作用。     

Effects of Exercise Intensity on Spatial Memory Performance and Hippocampal Synaptic Plasticity in Transient Brain Ischemic Rats

Memory impairment is commonly noted in stroke survivors, and can lead to delay of functional recovery. Exercise has been proved to improve memory in adult healthy subjects. Such beneficial effects are often suggested to relate to hippocampal synaptic plasticity, which is important for memory processing. Previous evidence showed that in normal rats, low intensity exercise can improve synaptic plasticity better than high intensity exercise. However, the effects of exercise intensities on hippocampal synaptic plasticity and spatial memory after brain ischemia remain unclear. In this study, we investigated such effects in brain ischemic rats. The middle cerebral artery occlusion (MCAO) procedure was used to induce brain ischemia. After the MCAO procedure, rats were randomly assigned to sedentary (Sed), low-intensity exercise (Low-Ex), or high-intensity exercise (High-Ex) group. Treadmill training began from the second day post MCAO procedure, 30 min/day for 14 consecutive days for the exercise groups. The Low-Ex group was trained at the speed of 8 m/min, while the High-Ex group at the speed of 20 m/min. The spatial memory, hippocampal brain-derived neurotrophic factor (BDNF), synapsin-I, postsynaptic density protein 95 (PSD-95), and dendritic structures were examined to document the effects. Serum corticosterone level was also quantified as stress marker. Our results showed the Low-Ex group, but not the High-Ex group, demonstrated better spatial memory performance than the Sed group. Dendritic complexity and the levels of BDNF and PSD-95 increased significantly only in the Low-Ex group as compared with the Sed group in bilateral hippocampus. Notably, increased level of corticosterone was found in the High-Ex group, implicating higher stress response. In conclusion, after brain ischemia, low intensity exercise may result in better synaptic plasticity and spatial memory performance than high intensity exercise; therefore, the intensity is suggested to be considered during exercise training.