Sepsis facilitates brain serotonin activity and impairs learning ability in rats

Sepsis often provokes various neurological disorders. Because many neurologic symptoms are caused by changes in neurotransmissions, we investigated the relationship between behavioral alterations and changes in activities of the monoaminergic systems in rats. Sepsis was induced by cecal ligation and puncture. A step-through passive avoidance test was used for the behavioral evaluation. Passive avoidance retention in animals subjected to learning immediately before the septic or sham operation was examined after 24 or 48 h. Retention performance in animals subjected to learning 24 h after the operation was also examined after a further 24 h. Plasma concentrations of amino acids were determined 24 h after the operation. The activities of the brain monoaminergic systems were evaluated by ratios of metabolites to monoamines. Marked damage was found in the septic rats in the blood analysis 24 h after the operation. The plasma concentrations of tyrosine and arginine in the septic rats were decreased to 69% and 70% of those in the sham-operated animals, respectively. Retention performance was impaired in the septic rats when they were subjected to learning 24 h after the operation, but it was not impaired when animals were subjected to learning before the septic operation. The brain concentration of serotonin was increased in the cerebral cortex, striatum, and hippocampus 48 h after the septic operation, but not after 24 h. The concentration of 5-hydroxyindoleacetic acid, a metabolite of serotonin, was increased in the above three regions both 24 and 48 h after the operation, but not in the hypothalamus. Facilitation of the serotonergic activity in the telencephalon and hippocampus is suggested to be involved in the impairment of learning ability in sepsis.     

Impaired cerebrovascular reactivity after cortical spreading depression in rats: Restoration by nitric oxide or cGMP

We investigated the role of the NO/cGMP system in the vasodilatory response to hypercapnia after cortical spreading depression (CSD) in barbiturate anesthetized rats in vivo. Regional cerebral blood flow (rCBF) was measured by laser Doppler flowmetry (LDF). Hypercapnia (arterial pCO2 50-60 mm Hg) increased rCBF by 2.8+/-1.0%/mm Hg (n = 34). Fifteen minutes after CSD, resting rCBF was reduced to 87%, and rCBF response to hypercapnia was abolished (p < 0.001, n = 28). Within 1 h after CSD, only little restoration of vascular reactivity occurred. Topical application of the NO-donors S-nitroso-N-acetylpenicillamine (SNAP), 3-morpholinosydnonimine (SIN1), or spermine/NO complex (Sperm/NO), or of the cell permeable guanosine 3',5'-cyclic monophosphate (cGMP) analogue 8-Br-cGMP reestablished resting rCBF to values measured before CSD, and reversed CSD-induced attenuation of the cerebrovascular response to hypercapnia. Restoration of resting rCBF to pre-CSD level by the NO-independent vasodilator papaverine had no effect on the attenuated hypercapnic response. In conclusion, we have shown that the compromised vascular reactivity to hypercapnia after CSD can be reversed to normal reactivity by restoration of the basal NO or cGMP concentration in the cortex, suggesting a reduction of the cerebrovascular NO or cGMP concentration following CSD.     

Cerebral ammonia metabolism in normal and hyperammonemic rats

Brain ammonia is generated from many enzymatic reactions, including glutaminase, glutamate dehydrogenase, and the purine nucleotide cycle. In contrast, the brain possesses only one major enzyme for the removal of exogenous ammonia, i.e., glutamine synthetase. Thus, following administration of [¹³N]ammonia to rats [via either the carotid artery or cerebrospinal fluid (csf)], most metabolized label was in glutamine (amide) and little was in glutamate (plus aspartate). Since blood-and csf-borne ammonia are converted to glutamine largely, if not entirely, in the astrocytes, it is not possible from these types of experiments to predict with certainty the metabolic fate of the bulk of endogenously produced ammonia. By comparing the specific activity ofl-[¹³N]glutamate to that ofl-[amine-¹³N]glutamine following intracarotid [¹³N]ammonia administration it was concluded that metabolic compartmentation is no longer intact in the brains of rats treated with the glutamine synthetase inhibitorl-methionine-SR-sulfoximine (MSO) and that blood and brain ammonia pools mix in such animals. In MSO-treated animals, recovery of label in brain was low (～20% of controls), and of the label remaining, a prominent portion was in glutamine (amide) (despite an 87% decrease in brain glutamine synthetase activity). These data are consistent with the hypothesis that glutamine synthetase is the major enzyme for metabolism of endogenously—as well as exogenously—produced ammonia. The rate of turnover of blood-derived ammonia to glutamine in normal rat brain is extremely rapid (t _1/2≤3 s), but is slowed in the brains of chronically (12–14-wk portacaval-shunted) or acutely (urease-treated) hyperammonemic rats (t _1/2≤10 s). The slowed turnover rate may be caused by an increased astrocytic ammonia, decreased glutamine synthetase activity, or both. In the hyperammonemic rat brain, glutamine synthetase is still the only important enzyme for the removal of blood-borne ammonia. Hyperammonemia causes an increase in brain lactate/pyruvate ratios and decreases in brain glutamate and brainstem ATP, consistent with an interference with the malate-aspartate shuttle. In vitro, pathological levels of ammonia also inhibit brain α-ketoglutarate dehydrogenase complex and, less strongly, pyruvate dehydrogenase complex. The rat brain does not adapt to prolonged hyperammonemia by increasing its glutamine synthetase activity. Therefore, since the brain only has a limited capacity to buffer against excess ammonia, it is important that diseases in which hyper-ammonemia is a prominent feature be treated to reduce the associated hyperammonemia as much as possible.     

Long-term effects of seizures in neonatal rats on spatial learning ability and N-methyl-D-aspartate receptor expression in the brain

For the purpose of investigating the long-term effects of seizures in neonatal rats on spatial learning ability and N-methyl-D-aspartate (NMDA) receptor expression in adult rat brain, a seizure was induced by inhalant flurothyl daily in neonatal Wistar rats from postnatal day 6 (P6). The authors assigned six rats each averagely into the single-seizure group, the recurrent-seizure group (seizures induced in six consecutive days), and the control group. During P60 to P65, the rats were tested for spatial learning ability with the Morris water maze task. On P75, the authors examined protein expression of the NMDA receptor (NR) subunits, NR1, 2A, 2B, 2C, and 2D, in the cerebral cortex and hippocampus by Western blotting analysis. On P65, the escape latencies from the water maze of the rats in the recurrent-seizure group were significantly longer than those of the control rats, but there was no difference between the single-seizure group and the control group. NR subunit expression in the cerebral cortex and hippocampus of the rats with single seizure was similar to those in the control rats. Compared with the control rats, the protein expressions of NR1, NR2A and NR2B in the cerebral cortex and NR2A in the hippocampus of the recurrent-seizure group was significantly decreased, but NR2C protein expression in the cerebral cortex and hippocampus significantly increased. Recurrent seizures induced in neonatal rats might cause long-term spatial learning ability deficit and modify NR expression in the cerebral cortex and hippocampus of adult rats. The results suggest that abnormal NR expression might play an important role in long-term spatial learning ability deficit induced by recurrent seizures in early life.     

Early ventriculoperitoneal shunt — effects on learning ability and synaptogenesis of the brain in congenitally hydrocephalic HTX rats

The learning ability of congenitally hydrocephalic HTX rats in which hydrocephalus had been arrested by the insertion of a V-P shunt 7 days after birth (early shunt) was assessed by means of the light-darkness discrimination test when the animals reached maturity. Early shunt placement resulted in marked reduction in size of abnormally enlarged ventricles and the prevention of both decreasing spine density and decay of synaptic vesicle protein (SVP-38) in the affected cerebral cortex. The learning ability of such animals was also found not to be impaired compared with that of animals in a sham-operation group. On the basis of these investigations, it is concluded that early shunt placement may have a beneficial role in preventing not only impairment of synaptogenesis of the brain by progressing hydrocephalus, but also learning disability. Recent biochemical investigation of the developing brains of hydrocephalic HTX rats revealed problems that cannot be resolved by early shunt insertion, and these are also discussed.Presented at the Consensus Conference: Hydrocephalus '92, Assisi, Italy, 26–30 April 1992     

苯妥英钠对实验性癫痫脑cAMP、cGMP的影响研究

采用戊四氮诱发大鼠癫痫模型，用苯妥因预处理大白鼠，用放免法测定各组大鼠额叶皮层及海马中ｃＡＭＰ，ｃＧＭＰ的含量。结果发现：预处理组额叶皮层ｃＡＭＰ，ｃＧＭＰ与癫痫组中相应指标显著下降，海马ｃＧＭＰ的较癫痫组显著下降。提示ＰＨＴ可能控制癫痫是稳定ｃＡＭＰ，ｃＧＭＰ水平有关。     

Changes of learning and memory ability associated with neuronal nitric oxide synthase in brain tissues of rats with acute alcoholism

INTRODUCTION The discovery of nitric oxide was the greatest achievement of neuro- biology in late 20th century. The discoverers were awarded the Nobel Prize in Physiology and Medicine. Publications on all aspects of nitric oxide run into thousands. Nevert…     

Effects of Lamotrigine on brain nitrite and cGMP levels during focal cerebral ischemia in rats

Glutamate receptor antagonists are protective in animal models of focal cerebral ischemia. Lamotrigine (3,5-diamino-6-[2,3-dichlorophenyl]-1,2,4-triazine) is an anticonvulsant drug that blocks voltage-gated sodium channels and inhibits the ischemia-induced release of glutamate. Experiments in primary neuronal cultures implicate nitric oxide (NO) as a mediator of glutamatergic neurotoxicity acting via N-Methyl- d -Aspartate (NMDA) receptors. The effect of glutamate release inhibitor, Lamotrigine upon NO and cGMP production has been examined in focal cerebral ischemia in rats. Focal cerebral ischemia was produced by the permanent occlusion of right middle cerebral artery (MCA) in urethane anesthetized rats. A number of indicators of brain NO production (nitrite, cGMP) were determined in ipsilateral and contralateral cerebral cortex and cerebellum after 0, 10, 60 min of focal cerebral ischemia. The same parameters were measured in rats treated with Lamotrigine (20 mg/kg, i.p.) 30 min before or just after the occlusion of the right MCA.     

慢性前脑缺血大鼠学习、记忆功能的研究

目的 研究慢性持续性脑血流量下降对大鼠学习、记忆功能的影响。方法 采用双侧颈总动脉永久结扎方法制备慢性前脑缺血动物模型；利用激光多普勒血流仪检测各组大鼠术后不同时间点（术后24h、7d、15d、30d、60d、90d、120d）额叶皮质、海马枢局部及血流量(rCBF）；采用被动回避性条件反射－－跳台试验检验各组大鼠（时间点同前）学习能力；利用水迷宫方法检验各组大鼠记忆功能。结果 大鼠术后额叶皮质、海马区的cCBF明显下降，以术后24h最明显，主后120d时仍明显 于正常，呈慢性持续性下降的趋势。同时各实验组大鼠学习、记忆能力也明显下降，且有随时间推移而逐渐加重的倾向。结论 慢性持续性脑血流量下降可导致实验大鼠出现进行性认知功能障碍。     

Effects of increasing serotonergic receptor activity in brain on analgesic activity in rats

In the rat, increasing serotonergic receptor activity or functional serotonin in the brain with inhibitors of serotonin reuptake (such as fluoxetine and chlorimipramine), with serotonin, or with the serotonin precursor, 5-hydroxytryptophan, in combination with the peripheral decarboxylase inhibitor benserazide had a significant analgesic effect shown by an increase in the latency to hind-paw lick in the hot plate test. The data indicate that activation of central serotonergic receptors with inhibitors of serotonin reuptake, serotonin, or the serotonin precursor produced pain inhibition.     

Striatal extracellular dopamine levels are not increased by hyperglycemic exacerbation of ischemic brain damage in rats

We tested the hypothesis that hyperglycemic exacerbation of incomplete forebrain ischemia is mediated by increased extracellular dopamine levels. Normoglycemic and hyperglycemic Sprgue—Dawley rats (eight each) with previously placed coaxial striatal microdialysis probes underwent 12 min of forebrain carotid artery occlusion and trimethaphan-induced hypotension. Microdialysis was performed before, during and for 6 h after ischemia, then perfusion-fixation was performed. Hyperglycemic rats had more severe postischemic damage in the caudate-putamen, neocortex, and hippocampus. Extracellular striatal dopamine levels were increased by ischemia, but were unaffected by hyperglycemia. These data show that hyperglycemic exacerbation of ischemic striatal damage does not depend on elevated extracellular dopamine levels.     

大鼠能量限制通过上调脂联素水平减轻脑缺血损伤

目的 能量限制(CR)可产生脑缺血耐受作用,但其详细机制尚不清楚.本研究主要探讨CR产生脑缺血耐受效应是否与脂联素(APN)合成水平有关.方法 SD大鼠分为两组:CR和自由饮食(AL)组.喂养4w后,行大脑中动脉阻断模型(MCAO),检测MCAO前后大鼠血清及脑组织APN、内皮型一氧化氮合酶(eNOS)和一氧化氮(NO)含量,并测定大鼠脑梗死容积和神经功能评分,观察大鼠体内APN含量与CR产生脑缺血耐受间的关系.结果 ①MCAO后神经功能评分显示,CR组大鼠神经功能评分明显好于AL组(P＜0.05);②MCAO后脑梗死容积测量结果显示,CR组大鼠脑梗死容积明显小于AL组(P＜0.05);③经ELISA检测,CR可显著促进大鼠体内APN合成(与AL组比较P＜0.05),并可增加MCAO后3h大鼠血清和脑内eNOS表达及NO含量(P＜0.05).结论 CR可能通过增加体内APN合成、上调eNOS表达和促进NO分泌产生脑缺血耐受效应.     

白藜芦醇对戊四氮致痫大鼠的学习记忆能力的影响

目的 研究白藜芦醇对戊四氮致痫大鼠的空间学习记忆能力的影响.方法 采用戊四氮亚惊厥剂量腹腔注射建立慢性癫痫模型,造模成功后予以白藜芦醇15 mg/kg灌胃干预10 d,行Morris 水迷宫实验测试大鼠的空间学习和记忆能力.结果 经28 d连续给药,18只大鼠符合Racine点燃标准,Res干预组大鼠痫性发作潜伏期明显延长,且其发作时间明显低于癫痫模型组、二甲基亚砜组,差异有统计学意义(P＜0.05).定位航行试验:实验第1、2d,各组大鼠逃避潜伏期差异没有统计学意义,而第3、4、5d癫痫模型组、二甲基亚砜组大鼠逃避潜伏期比正常对照组明显延长,Res干预组大鼠逃避潜伏期明显低于癫痫模型组、二甲基亚砜组,差异有统计学意义(P＜0.05).空间探索试验:将原站台撤去后,癫痫模型组、二甲基亚砜组穿越原站台次数和象限逗留时间,比正常对照组明显减少;同Res干预组相比减少,差异有统计学意义(P＜0.05).结论 白藜芦醇对戊四氮致痫大鼠具有抗癫痫和改善其空间学习记忆能力.     

3-硝基丙酸诱发肌张力障碍大鼠的相关脑区细胞外神经递质变化

目的 研究3-硝基丙酸(3-NP)诱发肌张力障碍大鼠相关核团的神经递质变化.方法 24只SD大鼠随机分为对照组和实验组,每组12只.实验组大鼠尾壳核注射3-NP4000 μmol,对照组尾壳核注射生理盐水4μl,3 d后对两组大鼠进行行为学评分,然后对尾壳核、苍白球内侧、苍白球外侧和丘脑底核行微透析,用高效液相色谱法测定透析液中的神经递质含量.结果 实验组尾壳核天冬氨酸及谷氨酸较对照组明显增加(P＜0.05),而甘氨酸及γ-氨基丁酸较对照组明显减少(P＜0.01);苍白球内侧细胞外神经递质较对照组均明显减少(P＜0.01);丘脑底核细胞外神经递质较对照组均明显增加(P＜0.05);苍白球外侧细胞外神经递质含量较对照组均无明显差异(P＞0.05).结论 3-NP可引起尾壳核神经递质变化,并通过直接和间接通路引起苍白球内侧及丘脑底核神经递质变化,从而诱发肌张力障碍.     

全脑照射后昆明鼠的学习、记忆力损伤及其变化规律

目的探讨全脑照射后鼠的学习、记忆力损伤及其变化规律。方法硫喷妥钠麻醉后,采用直线加速器10MeV电子线照射102只4～6周龄昆明鼠全脑;102只分为3组（每组34只）,照射剂量分别为20、10、5Gy。另设34只鼠为对照组（只麻醉不照射）。照射后第1、2、3、4、5天和第14、28、56、84天采用跳台法测定鼠的学习、记忆力。结果照射后第2、3、56天,20Gy组鼠受电击次数分别为（1.0±0.9）次、（0.9±0.6）次和（1.4±1.0）次,与对照组的差异均有非常显著性（P<0.01）。照射后第2,3天20Gy组受电击潜伏期分别为（64±87）s、（92±78）s,与对照组［（173±21）s,（175±16）s］的差异均有非常显著性（P<0.01）;第56天为（164±88）s,与对照组［（261±79）s］的差异有显著性,P<0.05。照射后第2天20Gy组受电击鼠的构成比为6/9,与对照组（11%）的差异有显著性（P<0.05）。20Gy组学习、记忆力损伤最重,10Gy组次之,5Gy组与对照组的差异无显著性。照射后鼠学习、记忆力损伤的规律照射后第2,3天学习、记忆力有明显损伤,第4～28天为暂时恢复期,第56天出现第2次损伤高峰,第84天后再次恢复。结论放射性脑损伤可使鼠的学习、记忆力明显下降,记忆力损伤程度及恢复快慢均与照射剂量相关。     

Basal and learning task-related brain oxidative metabolism in cirrhotic rats

Hepatic encephalopathy is a neurological complication observed in patients with liver disease. Subjects with hepatic encephalopathy can develop memory alterations. In order to investigate brain oxidative metabolism in an animal model of chronic cirrhosis and its modification after spatial working memory task, we determined the neural metabolic activity of several brain limbic system regions by cytochrome oxidase (COx) histochemistry and assessed the spatial working memory in the Morris water maze of rats with cirrhosis by administration of thioacetamide. This COx histochemistry was done in cirrhotic and control rats under basal conditions and after the spatial working memory task. The histochemical results showed differences in basal COx activity between control and cirrhotic rats in hippocampal and thalamic regions. In cirrhotic rats basal COx activity was increased in the CA1 and CA3 areas of the hippocampus and reduced in the anterodorsal and anteroventral thalamic nuclei. We found impaired spatial working memory in animals with cirrhosis. These animals showed absence of metabolic activation of the CA3 hippocampal subfield and the lateral mammillary nucleus and disturbance of COx activity in the medial mammillary nucleus and the anteroventral thalamus. These findings suggest that cirrhotic rats show spatial working memory deficits that could be related to the alteration of metabolic activity of neural regions thought to be involved in the processing of spatial memories.     

Conditional discrimination learning in rats with global ischaemic brain damage

Hippocampal cell loss was induced by the four-vessel occlusion (4VO) method, a model of global ischaemia. Global ischaemia for 15 min induced a selective damage to the CA1 subfield. Occlusion for 25 min produced a larger cell loss within the CA1 and more variably the CA2, CA3, the striatum and cortex. Ischaemic and sham control groups were assessed on two conditional discrimination tasks (presenting the conditional cues either in the choice arms or the start arm) and two spatial tasks (water maze and a simple spatial discrimination task). No significant effects were found on either of the spatial tasks (apart from the speed measure on the water maze). However, on the conditional discrimination task with the cues in the choice arms, animals with 25 min ischaemia learned the task significantly more slowly than the 15 min ischaemic and control groups. Results for the task with cues presented in the start arm differed according to choice of criterion for learning. With a standard criterion of 90% accuracy on one session controls were significantly superior to both ischaemic groups. However, in this task rats with 15 min occlusion showed the greatest impairment, and were significantly worse than both the controls and the 25 min occlusion group. These results suggest that hippocampal ischaemic damage disrupts the learning of conditional discrimination but not simple spatial tasks. No clear relationship between the extent of hippocampal cell loss and behavioural impairment was evident. These results highlight the critical importance of procedural factors in the assessment of cognitive impairment.     

Long-term impairment of learning ability in rats after an experimental hippocampal epileptiform syndrome

An epileptiform syndrome was induced in rats by injecting tetanus toxin into their hippocampi. Control rats received neutralized toxin. Groups of animals that had recovered from the overt signs of the syndrome, and whose hippocampal EEGs would have returned to normal, were trained on different learning tasks. The subjects were found to be slightly impaired in learning a light-discrimination task in a Y maze, the impairment involving their continuing to make sporadic errors for a longer time. They were impaired in reversing this task and they adhered to their strategies for more consecutive trials. They took twice as many trials as their controls to learn a delayed alternation task in a T maze. They learned a simple position task in a Y maze more easily than their controls, but were impaired in reversing the task. The results suggest that the epileptiform syndrome produced changes in hippocampal functioning which outlast by weeks the EEG abnormalities. We suggest that the frequent seizure activity in their hippocampi may have produced long-term interference with the basic synaptic mechanisms involved in learning. The long-term learning deficits show that seizures themselves in the absence of anticonvulsant drugs can affect learning ability.     

Lower in vivo brain extracellular GABA concentration in diabetic rats during forced swimming

Diabetic rats are more immobile during the forced-swimming test (FST) and GABAergic drugs reverse this behavior. We investigated if there is in vivo changes of GABA levels of diabetic rats during the FST. In vivo basal striatal GABA levels of streptozotocin diabetic rats are similar to non-diabetic rats. Non-diabetic rats presented a significant increase in GABA levels after the FST while the increase was delayed and lower in diabetic rats. These results suggest that diabetes may change GABA homeostasis and modify behavioral responses in an animal model of depression.