Long-term evaluation of cytoarchitectonic characteristics of prefrontal cortex pyramidal neurons, following global cerebral ischemia and neuroprotective melatonin treatment, in rats

Global cerebral ischemia induces alterations of working memory, as evidenced in the eight-arm radial maze, in the absence of significant changes of pyramidal neuron population in the prefrontal cortex. These alterations can be prevented by a neuroprotective melatonin treatment. Thus, the cytoarchitectonic characteristics of the pyramidal neurons located at layers III and V in the prefrontal cortex of rats that had been submitted 120 days earlier to acute global cerebral ischemia (15 min four-vessel occlusion), and melatonin (10 mg/(kgh) for 6h, i.v.) or vehicle administration, starting 30min after the end of cerebral blood flow interruption, were evaluated in order to gain information on the changes of the neural substrate underlying disruption of prefrontocortical functioning. Soma size, rough length and number of bifurcations of basilar and apical dendrites, as well as spine density and proportions of the different types of spines in a 50 microm length segment of a secondary dendrite branching from the apical and the basilar dendrites, of pyramidal neurons of the dorsal medial prefrontal cortex, were evaluated in Golgi material. A significant reduction of soma size, apical and basilar dendrite length, number of dendritic bifurcations, and spine density were observed in pyramidal neurons at layers III and V after cerebral ischemia, while these alterations were prevented by melatonin treatment. These cytoarchitectural differences between groups seem to underlie the observed alterations in spatial working memory of ischemic, vehicle-treated rats in the absence of pyramidal neuron loss, as well as the better display of these functions long after ischemia and melatonin neuroprotection.     

慢性脑缺血大鼠海马CA1区锥体细胞树突形态及树突棘密度的变化

目的: 研究慢性脑缺血大鼠海马CA1区锥体细胞树突形态及树突棘密度的变化。 方法: 对大鼠进行双侧颈总动脉永久性结扎(2VO)制备慢性脑缺血模型,分别于2周、4周、8周通过Morris水迷宫对各组大鼠进行行为学评价,筛选造模成功大鼠,进行Golgi染色,光镜下观察海马CA1区锥体细胞树突的分支、长度及树突棘密度的变化。结果: 与对照组相比,4周、8周模型组树突的分支及长度显著减少(P<0.01),各周模型组树突棘的密度均有显著减少(P<0.01);模型组内随着缺血时间延长,树突的分支及长度、树突棘密度均显著减少(P<0.05)。结论: 慢性脑缺血可导致海马CA1区锥体细胞树突及树突棘损伤性变化,从而构成进展性认知功能障碍的病理生理学基础。     

自噬标志性分子LC3B在大鼠全脑缺血复灌损伤中海马CA1区的表达及意义

目的　探讨自噬标志分子LC3B在大鼠全脑缺血复灌不同时间的表达以及对海马神经元损伤的影响。 方法　采用四血管法(4-vessel-occlusion,4-VO)法制作大鼠全脑缺血模型,随机将33只　SD大鼠分成假手术组和缺血再灌注组。在大鼠全脑缺血20 min后,分别恢复血流灌注30 min、1、2、4、6、8、12、24、48、72 h,用免疫组织化学法检测海马CA1区神经元LC3B的表达。 结果　LC3B在大鼠全脑缺血20 min复灌2 h开始表达,在复灌12 h表达到达高峰,之后逐渐减弱。 结论　自噬的激活介导了大鼠全脑缺血再灌注海马CA1区神经元的损伤死亡,长时间脑缺血再灌注损伤中自噬激活的时间更早及介导神经元的损伤更严重。     

Repetitive firing of CA1 hippocampal pyramidal cells elicited by dendritic glutamate: slow prepotentials and burst-pause pattern

Summary (1) In order to compare responses to dendritic vs. somatic depolarization, CA1 pyramidal cells in rat hippocampal slices were stimulated by iontophoresis of glutamate to sensitive spots in the dendrites, and by somatic current injection. (2) Low intensities of either stimulus elicited slow repetitive firing. Each action potential was preceded by a slow depolarizing prepotential (SPP), lasting 50–300 ms and was followed by fast (3–5 ms) and slow (more than 100 ms) afterhyperpolarizations (AHPs). The SPPs, and AHPs were indistinguishable for the two types of stimuli. (3) In response to strong depolarizations, most cells showed an initial burst of spikes, followed by a pause before the steady discharge. This pattern was elicited by both glutamate and current. (4) The input resistance usually increased 5–20% during subthreshold depolarizations by glutamate or current. In contrast, large doses of glutamate caused a slow decline in the resistance (up to 40%), which was larger than during comparable current-induced discharge, and the response was followed by a longer AHP. (5) It is concluded that both dendritic and somatic depolarization, induced by glutamate and current, respectively, can elicit sustained repetitive firing with SPPs, fast and slow AHPs and burst-pause pattern, thus, increasing the likelihood that these phenomena play a role during natural activation of CA1 cells.     

Rapid effects of adult-onset hypothyroidism on dendritic spines of pyramidal cells of the rat cerebral cortex

Summary We have previously shown (Ruiz-Marcos et al. 1980, 1982) that thyroidectomy (T) performed in rats at 40 days of age, well past the neonatal period of development, results by 80–90 days of age in a decrease of the number of spines along the shaft of pyramidal neurons with the cell body in layer V in the visual area of the cerebral cortex. We have here studied how soon after the operation an effect on spine number and distribution may be observed. We have found that the response of these neurons to T is very rapid: a decrease in the number of spines/shaft between T and age-paired controls (C) rats is statistically significant by the earliest period of observation, namely 5 days after T. These results may be related to those of Dembri et al. (1983) showing that T performed in adult rats decreases the activity of Type I RNA polymerase by 5 days after the operation. It is possible that T impairs the synthesis of some compound(s) necessary for the formation and maintenance of spines. The present results suggest that spine number is not a fixed structure of the apical shaft once brain development is over, but is in a state of continuous formation and degradation. We have further observed that the effect of T performed at 40 days of age is more pronounced in the distal part of the shaft than on the rest, a result similar to that found after neonatal T (Ruiz-Marcos et al. 1982). However, contrary to findings after early hypothyroidism, T at 40 days of age does not distort the distribution of spines along the shaft.     

Current-to-frequency transduction in CA1 hippocampal pyramidal cells: Slow prepotentials dominate the primary range firing

Summary (1)In order to study how hippocampal pyramidal cells transform a steady depolarization into discharges, CA1 pyramids (n = 32) were injected with 1.5 s long pulses of constant depolarizing current. (2) The firing in response to weak currents was in most cells, characterized by low frequency (0.2–5 Hz), slowly increasing depolarizations preceding each action potential (slow prepotentials, SPPs), a long latency (0.2–5 s) to the initial spike and lack of adaptation. (3) The SPPs, which lasted 30–2,000 ms, showed an increasing steepness with increasing current, and seemed to be a major regulating factor for the slow firing. (4) In response to stronger currents the discharge had a high initial frequency (100–350 Hz), followed by adaptation to steady state firing (5–50 Hz). Thirty of 32 cells showed a dip in the frequency (n = 5), or a pause (n = 25) lasting 250–1,000 ms between the initial burst of firing and the steady state. The pause occurred only at intermediate current strengths. (5) Additional spikes to the initial burst seemed to be recruited through the development of depolarizing waves. The initial slope of these waves resembled those of the SPPs. Similar waves occurred at the expected tune of occasionally missing spikes during steady state firing. (6) The variability (SD/mean) of the interspike intervals decreased with increasing frequency of firing. (7) The frequency-current (f/I) relation for the steady state firing showed a simple linear or convex shape, and lacked a secondary range. In contrast, the f/I plots for the initial few interspike intervals had both primary, secondary and tertiary ranges, like motoneurones.Supported by the Norwegian Research Council for Science and the Humanities and The National Institute of Health, USA     

Role of adenosine receptors in neuroprotective effect during global cerebral ischemia

Selective A₁ adenosine receptor agonists produced a considerable neuroprotective effect during global cerebral ischemia. The neuroprotective effect decreased in the order: A₁ agonists-NECA-adenosine-A_2A agonist CGS 21680, while selective A₃ adenosine receptor agonist was ineffective. Inhibitory analysis showed that A₁ adenosine receptors mediate the neuroprotective effect of CPA, are involved in the effects of NECA and adenosine (but not CGS 21680), and participate in natural resistance to cerebral ischemia. The role of A_2B adenosine receptors in the realization of neuroprotective effects was also demonstrated.     

(+)-Borneol is neuroprotective against permanent cerebral ischemia in rats by suppressing production of proinflammatory cytokines

Stroke is one of the leading causes of disability and death globally. It occurs when a major artery is occluded in the brain and leads to death of cells within the injured tissue. (+)-Borneol, a simple bicyclic monoterpene extracted from traditional Chinese medicine, is widely used in various types of diseases. However, no study has proved the effects of (+)-borneol on functional recovery from permanent ischemic stroke and the mechanism is still unknown. Here, we report that in the rat model of permanent cerebral ischemia, we found that (+)-borneol (1.0 mg/kg) significantly ameliorated infarct size and neurological scores via reducing the expression of inducible nitric oxide synthase (iNOS) and tumor necrosis factor-alpha (TNF-a) in a dose dependent manner. Notably, (+)-borneol showed long-term effects on the improvement of sensorimotor functions in the photothrombotic model of stroke, which decreased the number of foot faults in the grid-walking task and forelimb asymmetry scores in the cylinder task, at least in part through reducing loss of dendritic spines in the length, brunch number and density. These findings suggest that (+)-borneol could serve as a therapeutic target for ischemic stroke.     

Time course of caspase activation in selectively vulnerable brain areas following global cerebral ischemia due to cardiac arrest in rats

This study evaluated the time course of caspase activation in selectively vulnerable brain areas (hippocampus, nucleus reticularis thalami (NRT), cortex and striatum) following cardiopulmonary resuscitation (CPR) after global cerebral ischemia due to cardiac arrest (CA) in rats. Caspases are well known to play a crucial role in the apoptotic cascade and inflammatory syndromes and, therefore, represent potential therapeutic postischemic targets. Given the delayed neurodegeneration following CA, it is highly important to study the time course of caspase activation in regard to therapeutic interventions after CA. To assess caspase activity, in situ staining was applied to detect general caspase activity at 6h, 3d and 7d and caspase-3 activity at 3d after return of spontaneous circulation (ROSC). For detection of neuronal apoptosis, TUNEL staining was applied at 7d after ROSC. Distinct patterns of early caspase activation were observed at 6h and 3d in the NRT and striatum and of late activation at 7d in the hippocampal CA-1 sector. General caspase and caspase-3 activity correlated strongly at 3d after ROSC in all areas studied. At 7d, the TUNEL-positive neuron counts in the hippocampal CA-1 sector correlated strongly with caspase activation. In conclusion, general caspase and caspase-3 activity after 6 min of CA and the delayed occurrence of TUNEL-positive neurons strongly indicate that neuronal degeneration after CA is at least strongly associated with apoptosis. Therefore, postischemic antiapoptotic interventions might offer potential future therapeutic opportunities global cerebral ischemia due to CA.     

Ceramide from sphingomyelin hydrolysis differentially mediates mitogen-activated protein kinases (MAPKs) activation following cerebral ischemia in rat hippocampal CA1 subregion

Objective

To explore the role that ceramide plays in the activation of mitogen-activated protein kinases (MAPKs) during cerebral ischemia and reperfusion.

Methods

Rats were subjected to ischemia by the four-vessel occlusion (4-VO) method. The sphingomyelinase inhibitor TPCK was administered to the CA1 subregion of the rat hippocampus before inducing ischemia. Western blot was used to examine the activity of extracellular-signal regulated kinase (ERK) and c-Jun N-terminal protein kinase (JNK) using antibodies against ERK, JNK and diphosphorylated ERK and JNK.

Results

At 1h reperfusion post-ischemia, JNK reached its peak activity while ERK was undergoing a sharp inactivation (P < 0.05). The level of diphosphorylated JNK was significantly reduced but the sharp inactivation of ERK was visibly reversed (P < 0.05) by the sphingomyelinase inhibitor.

Conclusion

The ceramide signaling pathway is up-regulated through sphingomyelin hydrolysis in brain ischemia, promoting JNK activation and suppressing ERK activation, culminating in the ischemic lesion.     

神经病理性痛大鼠海马CA1区锥体神经元树突及树突棘的变化

目的:观察神经病理性痛条件下大鼠海马CA1区锥体神经元树突形态和树突棘密度的变化。方法:建立大鼠腰5脊神经结扎(L5 spinal nerve ligation,SNL)神经病理性痛模型,对照组为假手术组即只暴露腰5脊神经,不结扎。利用Von Frey纤维丝检测其50%机械性缩足阈值(paw withdrawal threshold,PWT),判断SNL模型是否成功。通过高尔基(Golgi)染色的方法观察SNL模型后14 d海马CA1区锥体神经元树突形态和树突棘密度的变化。结果:SNL模型组大鼠CA1区锥体神经元树突棘密度升高,与对照组相比有统计学差异(P0.05),而锥体神经元树突分支数无明显差异。结论:神经病理性痛会导致海马CA1区锥体神经元树突棘密度升高。     

大鼠脑缺血后突触超微结构的变化

目的：探讨脑缺血损伤对突触的影响。方法：采用大鼠，制成脑缺血模型，应用透射电镜观察大脑顶叶皮质突触的变化。结果：随着缺血时间的延长，神经毡内突触数目逐渐减少；突触结构中突触小泡、线粒体也发生改变。缺血48h，突触小泡减少，甚至消失；线粒体变性、减少乃至消失，嵴减少或消失呈空泡状。突触前后膜被破坏，典型的突触结构已不存在。结论：脑缺血后，随缺血时间延长，突触结构异常，突触密度下降。     

Transient enhancement of inhibitory synaptic transmission in hippocampal CA1 pyramidal neurons after cerebral ischemia

Pyramidal neurons in hippocampal CA1 regions are highly sensitive to cerebral ischemia. Alterations of excitatory and inhibitory synaptic transmission may contribute to the ischemia-induced neuronal degeneration. However, little is known about the changes of GABAergic synaptic transmission in the hippocampus following reperfusion. We examined the GABA_A receptor-mediated inhibitory postsynaptic currents (IPSCs) in CA1 pyramidal neurons 12 and 24 h after transient forebrain ischemia in rats. The amplitudes of evoked inhibitory postsynaptic currents (eIPSCs) were increased significantly 12 h after ischemia and returned to control levels 24 h following reperfusion. The potentiation of eIPSCs was accompanied by an increase of miniature inhibitory postsynaptic current (mIPSC) amplitude, and an enhanced response to exogenous application of GABA, indicating the involvement of postsynaptic mechanisms. Furthermore, there was no obvious change of the paired-pulse ratio (PPR) of eIPSCs and the frequency of mIPSCs, suggesting that the potentiation of eIPSCs might not be due to the increased presynaptic release. Blockade of adenosine A1 receptors led to a decrease of eIPSCs amplitude in post-ischemic neurons but not in control neurons, without affecting the frequency of mIPSCs and the PPR of eIPSCs. Thus, tonic activation of adenosine A1 receptors might, at least in part, contribute to the enhancement of inhibitory synaptic transmission in CA1 neurons after forebrain ischemia. The transient enhancement of inhibitory neurotransmission might temporarily protect CA1 pyramidal neurons, and delay the process of neuronal death after cerebral ischemia.     

巴曲酶对脑缺血再灌注大鼠海马CA1区的影响

目的 通过观察大鼠局灶性脑缺血再灌注不同时段，巴曲酶对海马CAl神经元及星形胶质细胞数目、形态等方面的影响，从而探讨巴曲酶对局灶性脑缺血再灌注损伤的保护作用。方法 采用改良的线栓法制备大脑中动脉阻塞(MACO)2h、不同再灌注时间段(3h、6h、12h、24h、48h、72h、7d)的大鼠短暂局灶性脑缺血(transient focal cerebral isehemia)模型，随机设立巴曲酶组(Bat)、生理盐水对照组(N．S)、假手术组(sham-operated)，通过HE染色及胶质原纤维酸性蛋白(GFAP)和神经元特异核抗原(NeuN)的免疫组化染色，观测CAl区神经元和星形胶质细胞的形态、数目的动态变化。结果巴曲酶能显提高再灌注早期(6～24h)CAl区GFAP阳性细胞的数目，再灌注7d组存活锥体细胞的数量较盐水对照组有明显提高，提示局灶性脑缺血后早期反应性星形胶质细胞的增多对维持神经元的存活有积极意义，巴曲酶对短暂局灶性脑缺血再灌注引起的海马CAl区延迟性神经元坏死(DND)有一定的抑制作用。     

Proliferating cells differentiate into neurons in the hippocampal CA1 region of gerbils after global cerebral ischemia

Maternal separation in early life can increase vulnerability to neuropsychiatric disorders over the lifespan. To investigate the effect of acupuncture on cell proliferation in the dentate gyrus (DG), 5-bromo-2'-deoxyuridine (BrdU)-immunohistochemistry was performed in maternally-separated rat pups. Maternal separation, for 7 days from postnatal day 14, induced a significant decrease of BrdU-immunoreactive cells in DG, while acupuncture treatment at acupoint Shenmen (HT7), at the end of the transverse crease of the ulnar wrist, resulted in the significant increase in the number of BrdU-positive cells in DG. However, acupuncture at acupoint ST36, near the knee joint, produced no increase in the number of BrdU-positive cells. These findings indicate that acupuncture at acupoint HT7 appears to stimulate cell proliferation, and we suggested that acupuncture may be useful in the treatment of diseases related to maternal separation.     

Role of apoptosis inducing factor (AIF) for hippocampal neuronal cell death following global cerebral ischemia in mice

The molecular mechanisms of neuronal cell death following circulatory arrest are still not fully understood. In the current study we investigated the role of apoptosis-inducing factor (AIF), a major caspase-independent mitochondrial cell death protein, for neuronal cell death following global cerebral ischemia (GCI). C57/Bl6 or low AIF expressing Harlequin mutant mice (AIF^low) and their wild-type littermates were subjected to 10 min of GCI. DNA damage, nuclear pathology, and localization of AIF were investigated 6, 24, and 72 h after GCI by TUNEL and DAPI staining, and immunohistochemistry, respectively. Cell death of hippocampal CA1 neurons following GCI was associated with nuclear translocation of AIF, nuclear pyknosis, and DNA fragmentation, i.e. ∼80% of all TUNEL-positive neurons had nuclear AIF staining. In AIF^low mice neuronal cell loss was reduced by 60% (p < 0.02). The current experiments suggest that AIF-mediated signaling represents a novel mechanism of neuronal cell death following GCI.     

Characterization of anxiety and habituation profile following global ischemia in rats

The purpose of the current study was to document the behavioral profile of ischemic rats in novel tasks including the elevated plus maze (EPM), the Vogel/conflict model of anxiety and novelty-induced feeding suppression paradigm as well as to further characterize using behavioral monitoring, the response of ischemic animals in existing paradigms such as the open field. Our findings revealed that ischemic animals spent significantly more time and made more entries in the open arm of the EPM as compared to sham animals, two behaviors indicative of decreased anxiety level. This anxiolytic effect appeared restricted to exploratory models of anxiety, as no differences in punished licking rate were observed between groups in the Vogel/conflict test. In the open field, behavioral monitoring revealed transient ischemia-induced hyperactivity, limited to the initial 15 min of a 30 min testing period. Increased activity in ischemic animals was primarily characterized by increased exploration and sniffing behavior with no significant alterations in rearing and grooming frequencies. Finally, using feeding behavior, our findings revealed a comparable rate of habituation to a novel environment in ischemic and sham rats. Taken together, these results suggest that ischemia-induced hyperactivity may involve a disinhibition to explore unfamiliar and/or mildly anxiogenic environments. However, the basis of such hyperactivity and the presence of habituation deficit following ischemia require further study and/or validation.     

慢性低压低氧暴露对小鼠海马CA1区神经元树突棘形态及细丝蛋白A表达的影响

目的:探讨低压低氧暴露对小鼠海马CA1区神经元树突棘形态及细丝蛋白A表达的影响。方法:6～8周龄C57BL/6雄性小鼠分为常氧暴露7 d组、常氧暴露14 d组、低压低氧暴露7 d组和低压低氧暴露14 d组。低压低氧暴露组置于低压舱模拟6 000 m海拔高原进行低压低氧暴露。Golgi染色法观察小鼠海马CA1区树突的分支数,以及基树突棘和顶树突棘长度和密度的变化; Western blot方法检测小鼠海马细丝蛋白A表达水平的变化;免疫组织荧光染色法检测小鼠海马CA1区细丝蛋白A的表达及分布变化。结果:与常氧暴露组相比,低压低氧暴露后,小鼠海马CA1区树突分支数的差异无统计学显著性,但基树突棘和顶树突棘的长度显著增加(P 0. 05),密度显著降低(P 0. 01)。低压低氧暴露后,小鼠海马细丝蛋白A表达水平低于常氧暴露组(P 0. 01或P0. 05)。免疫组织荧光染色显示细丝蛋白A在小鼠海马CA1区表达,低压低氧暴露后,海马CA1区细丝蛋白A表达水平降低(P 0. 05)。结论:慢性低压低氧暴露可影响小鼠海马CA1区细丝蛋白A表达,并导致海马CA1区神经元树突棘形态发生改变。     

脑缺血再灌注损伤的海马神经元对Bax、Bcl-2和Caspase-3的表达

目的：凋亡调控基因在脑缺血再灌后海马神经元的表达。方法：采用免疫组织化学的方法，观察 昆明小鼠双侧颈总动脉结扎7min后不同再灌时间组(24h组、48h组、72h组、7d组、14d组)海马CAl区神经元Bax、Bcl-2和Caspase-3的活性形式CM1的免疫反应活性。结果：Bax和CM1阳性神经元数在48h组最多，与其他各组相比差异有显著性(P＜0．01)，72h组明显下降，14d组完全消失；而Bcl-2阳性神经元数在48h组增多(与24h组相比，P＜0．01)，72h组下降，7d组再次上升(与72h组相比，P＜0．01)，14d组最多(与48h组相比，P＜0．01)。在24h、48h、72h、7d组，Bax阳性神经元多于Bcl-2阳性神经元(P＜0．05)，14d组则相反。结论：Bax和caspase-3在脑缺血再灌早期表达增强，然后下降以至消失，Bcl-2于再灌后期表达增强。Bax表达上调可能与Caspase-3激活相关。     

Heptamethoxyflavone,a citrus flavonoid,enhances brain-derived neurotrophic factor production and neurogenesis in the hippocampus following cerebral global ischemia in mice

In the present study using a transient global ischemia mouse model, we showed that (1) a citrus flavonoid 3,5,6,7,8,3′,4′-heptamethoxyflavone (HMF) induced the phosphorylation of extracellular signal-regulated kinases 1/2 (ERK1/2) and cAMP response element-binding protein (CREB) in the hippocampus after ischemia; (2) HMF increased the expression of brain-derived neurotrophic factor (BDNF), a representative neurotrophic factor in the central nervous system, in the hippocampal dentate gyrus, and most BDNF-positive cells were also stained with anti-glial fibrillary acidic protein (one of the major intermediate filament proteins of mature astrocytes) and (3) HMF increased doublecortin positive neuronal precursor cells in the dentate gyrus subventricular zone or subgranular zone. These results suggest that HMF has the ability to induce BDNF production in astrocytes and enhance neurogenesis after brain ischemia, which may be mediated by activation of ERK1/2 and CREB.