Hippocampal cell genesis does not correlate with spatial learning ability in aged rats

Aging in rodents is known to lead to deficits in spatial learning and memory, including decreased performance on the Morris water maze. Recent attention has focused on the possible role of adult hippocampal neurogenesis in regulating spatial learning and memory. Therefore, in this study, we have examined levels of hippocampal cell proliferation in relation to water maze performance in aged and young male Fischer 344 rats. Aged rats (24 months old) were divided into aged-unimpaired and aged-impaired groups based on comparison with performance of young animals. Animals received five daily injections of the thymidine-analog bromodeoxyuridine (BrdU) and were killed 1 week later. Total numbers of BrdU-labeled cells were quantified in the hippocampal dentate gyrus and hilus and were related to behavioral performance. Whereas aging was associated with a significant reduction in the number of BrdU-labeled cells, behavioral impairment with aging was not associated with a further reduction in BrdU labeling. In the context of aging, these finding do not support a direct relationship of adult hippocampal neurogenesis with learning and memory capability.     

Individual differences in spatial memory among aged rats are related to hippocampal PKCgamma immunoreactivity

We reported previously that the extent of spatial memory impairment among aged rats was correlated positively with levels of protein kinase Cgamma in hippocampal homogenates measured by quantitative Western blotting (Colombo et al., 1997). In the current study, immunocytochemistry was used to test whether the relationship between elevated PKC-gamma and memory impairment among aged rats could be localized further within regions of the hippocampus. Six- and 24-month-old male Long-Evans rats were first trained in the water maze on a standard place-learning task and then trained 2 weeks later on a transfer task designed for rapid acquisition. In comparison with young rats, aged rats with impaired spatial memory had increased PKCgamma-immunoreactivity (PKCgamma-ir) in CA1 of the hippocampus, but not the dentate gyrus. In addition, PKCgamma-ir in CA1 was correlated positively with spatial memory impairment among aged rats on the standard place-learning and the transfer training tasks. The current results are consistent with our previous report of PKCgamma in hippocampal homogenates, and show further that the relationships between PKCgamma-ir and memory impairments among aged rats are most evident in area CA1. Thus age-related impairments of spatial memory, as well as deficits in the flexible use of previously acquired information, may result from dysregulation of PKCgamma.     

Hippocampal dependent learning ability correlates with N-methyl-D-aspartate (NMDA) receptor levels in CA3 neurons of young and aged rats

Hippocampal N-methyl-D-Aspartate (NMDA) receptors mediate mechanisms of cellular plasticity critical for spatial learning in rats. The present study examined the relationship between spatial learning and NMDA receptor expression in discrete neuronal populations, as well as the degree to which putative age-related changes in NMDA receptors are coupled to the effects of normal aging on spatial learning. Young and aged Long-Evans rats were tested in a Morris water maze task that depends on the integrity of the hippocampus. Levels of NR1, the obligatory subunit for a functional NMDA receptor, were subsequently quantified both biochemically by Western blot in whole homogenized hippocampus, and immunocytochemically by using a high-resolution confocal laser scanning microscopy method. The latter approach allowed comprehensive, regional analysis of discrete elements of excitatory hippocampal circuitry. Neither method revealed global changes, nor were there region-specific differences in hippocampal NR1 levels between young and aged animals. However, across all subjects, individual differences in spatial learning ability correlated with NR1 immunofluorescence levels selectively in CA3 neurons of the hippocampus. Parallel confocal microscopic analysis of the GluR2 subunit of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid (AMPA) receptor failed to reveal reliable differences as a function of age or spatial learning ability. This analysis linking age, performance, and NR1 levels demonstrates that although dendritic NR1 is generally preserved in the aged rat hippocampus, levels of this receptor subunit in selective elements of hippocampal circuitry are linked to spatial learning. These findings suggest that NMDA receptor abundance in CA3 bears a critical relationship to learning mediated by the hippocampus throughout the life span.     

Nerve growth factor levels and choline acetyltransferase activity in the brain of aged rats with spatial memory impairments

Nerve growth factor (NGF) and choline acetyltransferase (ChAT) activity levels were measured in 7 different brain regions in young (3-month-old) and aged (2-years-old) female Sprague-Dawley rats. Prior to analysis the spatial learning ability of the aged rats was assessed in the Morris' water maze test. In the aged rats a significant, 15–30%, increase in NGF levels was observed in 4 regions (septum, cortex, olfactory bulb and cerebellum), whereas the levels in hippocampus, striatum and the brainstem were similar to those of the young rats. The NGF changes did not correlate with the behavioral performance within the aged group. Minor 15–30%, changes in ChAT activity were observed in striatum, brainstem and cerebellum, but these changes did not correlate with the changes in NGF levels in any region. The results indicate that brain NGF levels are maintained at a normal or supranormal levels in rats with severe learning and memory impairments. Ther results, therefore, do not support the view that the marked atrophy and cell loss in the forebrain cholinergic system that is known to occur in the behaviorally impaired aged rats is caused by a reduced availability of NGF in the cholinergic target areas. The results also indicate that the slightly increased levels of NGF are not sufficient to prevent the age-dependent atrophy of cholinergic neurons, although they might be important for the stimulation of compensatory functional changes in a situation where the system is undergoing progressive degeneration.     

Hippocampal synapsin isoform levels are linked to spatial memory enhancement by SGS742

Synapsins are essential proteins for synaptic plasticity and there is no information available for their role in cognitive enhancement (CE) of spatial memory formation. It was therefore the aim of the study to link individual synapsin proteins and their isoforms to spatial memory formation enhanced by SGS742 in the mouse. Extracted hippocampal proteins from a cognitive study treating OF1 mice with the cognitive enhancer SGS742 and tested in the Morris water maze, were run on two‐dimensional gel electrophoresis. Subsequently, protein spots were unambiguously identified by qQ‐TOF mass spectrometry. Quantification of proteins from four groups (NaCl‐treated mice, SGS742‐treated mice, SGS742‐treated yoked controls, and NaCl‐treated yoked controls) was carried out according to an in‐gel stable isotope labeling method. A total of 17 protein spots representing synapsin isoforms were identified and quantified. Using quantification of individual synapsin isoforms showed that these can be clearly assigned to CE by the GABA_B antagonist SGS742. Quantitative determination of individual synapsin isoform showed an increase in SGS742‐treated mice (mean ± SD) of ratios between light and heavy stable isotope labeled synapsin protein (SGS742 vs. controls: 2.19 ± 0.41 for synapsin Ia, and 1.41 ± 0.81 for synapsin IIa). Synapsins Ib and IIb were not linked to CE. The NaCl‐treated controls and the use of yoked controls that were ruling out swimming‐ and stress‐mediated changes of synapsins, unequivocally allow to propose a role for synapsins Ia and IIa in the mechanism of CE of spatial memory formation. © 2009 Wiley‐Liss, Inc.     

Testosterone,but not nonaromatizable dihydrotestosterone,improves working memory and alters nerve growth factor levels in aged male rats

Recent studies have suggested that testosterone levels are lower in men with Alzheimer's disease and that testosterone treatment improves cognition in older men. Since testosterone can be aromatized to estrogen, testosterone's effects could be due to conversion into estrogen. We treated aged male rats with either testosterone or dihydrotestosterone (DHT), the latter of which is not aromatized to estrogen, in order to determine whether these treatments improve spatial working and reference memory as assessed in the water radial arm maze. We also tested whether such effects are related to beta-amyloid levels in the hippocampus or neurotrophin levels in the hippocampus, entorhinal cortex, frontal cortex, or striatum. Aged rats made more errors than young rats on all memory measures. Testosterone, but not DHT, improved working memory and decreased hippocampal NGF protein in aged rats, while having no effect on beta-amyloid. However, higher beta-amyloid levels were correlated with poorer working memory performance in young rats. Neurotrophin levels in entorhinal cortex were positively correlated with errors for all memory measures in androgen-treated rats. Similar to findings in human studies, in our study androgen treatment lowered circulating estradiol levels in aged rats, suggesting that androgen treatment exerts feedback to the hypothalamic pituitary axis and that conversion to estrogen may not be the underlying biological mechanism of testosterone's effects on memory and growth factor levels. The ratio of estradiol to testosterone, or the actions of the aromatase enzyme itself, may be responsible for the observed effects. These data support the hypothesis that testosterone therapy in aging men may provide positive effects on cognition and that neural regions that are linked to cognition, such as the hippocampus and/or entorhinal cortex, may be involved in such effects.     

Hippocampal lesioned rats are able to learn a spatial position using non-spatial strategies

In the last two decades, many experiments have demonstrated that the hippocampus plays a role in the learning and processing of spatial and contextual information. Despite these demonstrations, some recent publications have indicated that the hippocampus is not the only structure involved in spatial learning and that even after hippocampal lesions, rats can perform spatial tasks. However, it is not well established whether animals with hippocampal dysfunction still have some spatial learning capacities or develop non-spatial solutions; these may require lengthier acquisition training. We now report the effects of conventional, dorsal hippocampal ablation on rats' performance on the water maze. We tested rats using a short (4 days) versus a long (16 days) acquisition period. We demonstrated that animals with dorsal hippocampal lesions have some residual capacity for learning the localization of a hidden escape platform in a pool during both a reference memory task and a working memory task. The animals with dorsal hippocampal lesions learned to escape at a fixed location, but only with extended training. It is suggested that these animals used non-spatial strategies to compensate for a spatial memory impairment. The results are discussed with respect to the experimental procedure and the strategy applied by the lesioned rats.     

Hippocampal acetylcholine release correlates with spatial learning performance in freely moving rats

To assess the activity of septohippocampal cholinergic neurons during the learning of a radial-arm maze task we measured changes in extracellular acetylcholine levels in the hippocampus by means of the vertical microdialysis technique. During the 12 days spent learning the spatial task the extracellular concentration of acetylcholine in the hippocampus was monitored while rats performed the test. One week before radial-arm maze training a guide cannula was implanted unilaterally in the hippocampus. On each day of testing a removable microdialysis probe was inserted through the guide cannula and the dialysate was collected during the test performance. The concentration of acetylcholine in the dialysate was detected by means of a high-performance liquid chromatograph coupled to an electrochemical detector. We found that hippocampal acetylcholine release progressively increased from 139% to 245% during the 12 days of radial-maze learning and the magnitude of change in acetylcholine output was positively correlated with spatial memory performance, thus suggesting that changes in the functioning of these neurons are involved in learning.     

Circuit-specific alterations in hippocampal synaptophysin immunoreactivity predict spatial learning impairment in aged rats.

The present study examined the long-standing concept that changes in hippocampal circuitry contribute to age-related learning impairment. Individual differences in spatial learning were documented in young and aged Long-Evans rats by using a hippocampal-dependent version of the Morris water maze. Postmortem analysis used a confocal laser-scanning microscopy method to quantify changes in immunofluorescence staining for the presynaptic vesicle glycoprotein, synaptophysin (SYN), in the principal relays of hippocampal circuitry. Comparisons based on chronological age alone failed to reveal a reliable difference in the intensity of SYN staining in any region that was examined. In contrast, aged subjects with spatial learning deficits displayed significant reductions in SYN immunoreactivity in CA3 lacunosum-moleculare (LM) relative to either young controls or age-matched rats with preserved learning. SYN intensity values for the latter groups were indistinguishable. In addition, individual differences in spatial learning capacity among the aged rats correlated with levels of SYN staining selectively in three regions: outer and middle portions of the dentate gyrus molecular layer and CA3-LM. The cross-sectional area of SYN labeling, by comparison, was not reliably affected in relation cognitive status. These findings are the first to demonstrate that a circuit-specific pattern of variability in the connectional organization of the hippocampus is coupled to individual differences in the cognitive outcome of normal aging. The regional specificity of these effects suggests that a decline in the fidelity of input to the hippocampus from the entorhinal cortex may play a critical role.     

不同鼠龄大鼠成纤维细胞生长因子及相关基因在牵引成骨局部的表达

背景：成纤维细胞生长因子及相关基因表达在骨再生和修复过程中起着重要的作用。 目的：通过对不同鼠龄大鼠在同样条件下牵引成骨的比较，进一步验证成纤维细胞生长因子及相关基因在成骨局部的表达水平与年龄的关系，及其在大鼠胫骨牵引成骨过程中对新骨形成的影响。 设计、时间及地点：随机对照动物实验，于2007-01/03在中南大学附属三医院中心实验室完成。 材料：健康雄性SD大鼠20只，3月龄和12月龄各10只，分为青年组和老年组。 方法：所有大鼠接受左胫骨中上段低能截骨，安置体外延长固定架。第2天起开始每天进行胫骨延长，速率为0.2 mm， 2次/d，共14 d。第15天，处死大鼠，采集胫骨标本。 主要观察指标：以X射线片定量分析新骨密度和新骨面积；以组织学定量分析骨内膜成骨和骨膜成骨；以反转录-聚合酶链反应分析成纤维细胞生长因子及相关基因的表达。 结果：青年组大鼠牵引区的新生成骨面积和新生骨密度，以及骨内膜成骨和骨膜成骨百分比均显著高与老年组大鼠(P < 0.05或0.01)；成纤维细胞生长因子及相关基因在老年组大鼠的表达水平明显低于青年组。 结论：老年大鼠骨形成障碍可能与局部生长因子表达降低，从而导致成骨细胞功能低下密切相关。     

Effect of nerve growth factor on the lesioned septohippocampal cholinergic system of aged rats

Nerve growth factor (NGF) was injected intraventricularly into aged (24 months) rats with unilateral lesions of the lateral fimbria. The activity of choline acetyltransferase (ChAT) was determined in the septum and hippocampus from the normal unlesioned rats, lesioned and cytochrome c-treated rats (controls), and lesioned and NGF-treated rats at different times after the lesion. NGF-injection for 15 days after the lesion resulted in an increase of the ChAT activity in both the contralateral hippocampus and the entire septum, to about 130% of that in the normal animals, but resulted in a slight increase in the ipsilateral lesioned hippocampus, when compared to the activity in the ipsilateral side of the cytochrome c-treated controls. NGF-injection for 30 days after the lesion resulted in a 48% increase of the ChAT activity in the ipsilateral hippocampus as compared to cytochrome c-treated controls, but failed to result in a significant increase in the contralateral hippocampus. These findings indicate that atrophic cholinergic neurons in aged animals are similarly responsive to NGF treatment, like these in the young animals. Moreover, these findings suggest that the responses of basal forebrain cholinergic neurons to NGF treatment varies with time after the lesion and imply that the NGF administration can promote the collateral sprouting from spared cholinergic fibers after the lesion in the aged forebrain.     

Chronic nerve growth factor treatment of normotensive rats.

The objectives of this study were to examine the effects of chronic nerve growth factor (NGF) administration on vascular innervation and blood pressure in neonatal rats. Newborn Wistar-Kyoto (WKY) rats bred from normotensive parents were chronically treated with NGF for 8 weeks. Littermate controls received saline. Sympathetic ganglia of treated animals were greatly enlarged and in the superior cervical ganglion neuronal numbers were increased 200% and nuclear areas by 46%. The catecholamine contents of several sympathetically innervated tissues were determined biochemically and found to be significantly elevated in mesenteric arteries, aorta, ileum, adrenal and salivary glands from treated compared to control animals. The catecholamine concentrations were similar to, or exceeded those of the spontaneously hypertensive rat. Histochemically, an aberrant nerve supply was evident occupying a greater volume of the adventitia of the caudal artery and mesenteric arteries. In addition, nerve fibres could be seen penetrating the vessel wall to emerge within the lumen of mesenteric blood vessels. Analysis of the smooth muscle wall of the caudal artery revealed that a small but significantly hyperplastic response had been induced. Systolic blood pressures of NGF-treated and control animals were taken at one week intervals from 5 to 8 weeks of age utilizing the tail cuff method. The blood pressure of treated animals were within the normotensive range. It is concluded that chronic NGF treatment leads to changes in vascular innervation and muscle thickness that are similar to those seen in hypertensive animals. Furthermore, the results suggest the elevated levels of NGF seen in peripheral tissues of the spontaneously hypertensive rat are likely to be responsible for the hyperinnervation and resulting hyperplastic responses within vascular tissues, but not exclusively responsible for the elevated blood pressure.     

Calcium chelation improves spatial learning and synaptic plasticity in aged rats

Impaired regulation of intracellular calcium is thought to adversely affect synaptic plasticity and cognition in the aged brain. Comparing young (2-3 months) and aged (23-26 months) Fisher 344 rats, stratum radiatum-evoked CA1 field EPSPs were smaller and long-term potentiation (LTP) was diminished in aged hippocampal slices. Resting calcium, in presynaptic axonal terminals in the CA1 stratum radiatum area, was elevated in aged slices. Loading the slice with the calcium chelator, BAPTA-AM, depressed LTP in young slices, but enhanced this plasticity in old slices. Forty-five minutes following LTP-inducing high frequency stimulation, resting calcium levels were significantly increased in both young and old presynaptic terminals, and significantly reduced by pretreatment with BAPTA-AM. In vivo, intraperitoneal administration of BAPTA-AM prior to training in the reference memory version of the Morris water maze test, significantly improved the acquisition of spatial learning in aged animals, without a significant effect in young rats. These results support the hypothesis that increasing intracellular neuronal buffering power for calcium in aged rats ameliorates age-related impaired synaptic plasticity and learning.     

幼龄和老龄大鼠液压颅脑伤后NGFmRNA表达差异

目的观察幼龄和老龄大鼠颅脑损伤后神经生长因子信使RNA(nerve growth factor mRNA ,NGFmRNA)表达差异,探讨老年动物中枢神经损伤后神经功能缺失较多的病理生理机制,以及改善老年颅脑损伤预后的方法.方法采用大鼠侧方液压打击颅脑损伤模型,应用原位杂交方法和计算机显微图象分析技术,比较幼龄(2～3个月)和老龄(15个月)大鼠脑损伤后12 h脑内 NGFmRNA 表达水平的差异,并用β2 受体激动剂克仑特罗(clenbuterol,CLE)作为干预手段,观察其对幼龄和老龄大鼠受损脑组织 NGFmRNA 表达的调节作用.结果液压打击伤后12 h,两组大鼠损伤脑组织NGFmRNA表达均有不同程度的增加,但是老龄鼠损伤侧大脑皮层NGFmRNA表达明显低于幼龄鼠( P <0.05);伤后立即应用CLE(0.5 mg/kg,腹腔注射)并不提高幼龄大鼠受伤脑组织NGFmRNA的表达,但可显著提高老龄鼠NGFmRNA的表达( P <0.01).结论脑损伤早期老龄鼠NGFmRNA表达较低提示老年动物受损脑组织修复能力减低,这为我们认识临床上老年颅脑损伤后神经功能缺失较多的原因提供了帮助;CLE能够增加老龄大鼠受损脑组织NGFmRNA表达并可能由此提高老年动物的神经修复能力.     

Hippocampal synaptic plasticity and spatial learning are impaired in a rat model of sleep fragmentation

Sleep fragmentation, a symptom in many clinical disorders, leads to cognitive impairments. To investigate the mechanisms by which sleep fragmentation results in memory impairments, rats were awakened once every 2 min via 30 s of slow movement on an automated treadmill. Within 1 h of this sleep interruption (SI) schedule, rats began to sleep in the 90-s periods without treadmill movement. Total non-rapid eye movement sleep (NREM) sleep time did not change over the 24 h of SI, although there was a significant decline in rapid eye movement sleep (REM) sleep and a corresponding increase in time spent awake. In the SI group, the mean duration of sleep episodes decreased and delta activity during periods of wake increased. Control rats either lived in the treadmill without movement (cage controls, CC), or had 10-min periods of movement followed by 30 min of non-movement allowing deep/continuous sleep (exercise controls, EC). EC did not differ from baseline in the total time spent in each vigilance state. Hippocampal long-term potentiation (LTP), a long-lasting change in synaptic efficacy thought to underlie declarative memory formation, was absent in rats exposed to 24 and 72 h SI. In contrast, LTP was normal in EC rats. However, long-term depression and paired-pulse facilitation were unaltered by 24 h SI. Twenty-four hour SI also impaired acquisition of spatial learning in the hippocampus-dependent water maze test. Twenty-four hour SI elevated plasma corticosterone (CORT) to levels previously shown to enhance LTP (125 ng/mL). The results suggest that sleep fragmentation negatively impacts spatial learning. Loss of N-methyl-D-aspartate (NMDA) receptor-dependent LTP in the hippocampal CA1 region may be one mechanism involved in this deficit.     

Peripheral nerve abnormalities related to galactose administration in rats.

Electrophysiological, biochemical, and morphometric observations were made on the peripheral nerves of rats after galactose feeding. Motor nerve conduction velocity was found to be reduced. This was associated with an accumulation of galactitol in the peripheral nerves and a diminution in their myoinositol content. An increased water content and fascicular area, taken in conjunction with a probable increase in the area of the endoneurial spaces, indicated overhydration of the peripheral nerves. Morphometric observations on the myelinated fibre population in the tibial nerve showed no loss of fibres and although both the maximal and the average diameter of the myelinated fibres was slightly less than in age-matched controls, this was insufficient to explain the reduction in conduction velocity. Segmental demyelination was not detected and the relationship between myelin thickness and axon circumference was not altered. Electron microscope observations revealed no ultrastructural changes in the myelinated fibres and, in particular, no abnormalities at the nodes of Ranvier or indication of abnormal hydration of the Schwann cells. The relevance of these findings to the peripheral nerve changes in human and experimental diabetes is discussed.     

神经生长因子对脑缺血大鼠学习与记忆的影响

目的为了观察神经生长因子（NGF）对脑缺血大鼠学习与记忆的影响和海马内N-甲基-D-天门冬氨酸受体NR2A/B亚zhanghaopeng（NR2A/B）表达的变化。方法本研究将48只成年雄性SD大鼠分为正常组（n=12）、假手术组（n=12）、慢性脑缺血组（n=12）、NGF处理组（n=12）。于造模后开始腹腔注射0.25 ug/100 g NGF,假手术组和慢性脑缺血组腹腔注射等量生理盐水,均1次/d,共21 d。用Morris水迷宫和＂＂Y＂迷宫作业测试其空间学习与记忆成绩,再采用Western blot方法分析海马的NR2A、NR2B的表达。结果①Morris水迷宫测试：模型组大鼠寻找平台的潜伏期较假手术组明显延长,NGF处理组大鼠寻找平台的潜伏期较模型组明显缩短;＂Y＂迷宫测试：模型组大鼠学会躲避电击的正确次数较假手术组明显减少,NGF处理组大鼠学会躲避电击的正确次数较模型组明显增多;②模型组NR2A表达水平较假手术组明显降低,而NR2B明显升高;NGF处理组海马内NR2A表达水平较模型组明显上调,而NR2B明显下调。结论神经生长因子可增强学习与记忆,海马内N-甲基-D-天门冬氨酸（NMDA）受体表达变化可能是影响学习与记忆的机制之一。     

No nerve growth factor response to treatment with memantine in adult rats

Summary. Nerve growth factor (NGF) is the most widely examined neurotrophin in the experimental models of Alzheimers disease (AD) and has been shown to prevent the retrograde degeneration of cholinergic neurons. In this study we examined NGF and cholineacetyltransferase (ChAT) changes in several rat brain regions after excitotoxic lesion of the entorhinal cortex with quinolinic acid and tested the effect of memantine on spatial learning in the radial maze after lesion. We observed a significant increase (+26%, p=0.02) of NGF concentrations in the hippocampus of the lesioned rats when compared to sham-lesioned rats. Chronic treatment with memantine showed no significant effect on the NGF increase in the hippocampus (p=0.72). The ChAT activity was significantly increased in the lesioned rats when compared to controls (+16%, p<0.05) and did not depend on treatment with memantine. In spite of this, memantine improved performance of the radial maze. This indicates that memory improving effects of memantine observed in experimental animals and in clinical studies are probably not related to changes in brain NGF content, whereas the observed NGF increase in the denervated hippocampus is probably trauma-related reflecting impaired retrograde transport of hippocampal NGF.Present address: Solvay Pharmaceuticals BV, Weesp, NiederlandePresent address: Institute of Pharmacology PAN, Cracow, Poland     

Effect of calcitonin gene-related peptide and nerve growth factor on spatial learning and memory abilities of rats following focal cerebral ischemia/reperfusion

BACKGROUND: Calcitonin gene-related peptide (CGRP) and nerve growth actor (NGF) cam improve spatial learning and memory abilities of rats with cerebral ischemia/reperfusion; however, the effect of combination of them on relieving learning and memory injury following cerebral ischemia/reperfusion should be further studied. OBJECTIVE: To study the effects of exogenous CGRP and NGF on learning and memory abilities of rats with focal cerebral ischemia/reperfusion. DESIGN: Randomized controlled animal study. SETTING: Department of Neurosurgery, the Second Hospital of Xiamen; Department of Neurosurgery, the Second Affiliated Hospital of China Medical University; Department of Neurobiology, Basic Medical College of China Medical University. MATERIALS: A total of 30 healthy male SD rats, aged 8 weeks, of clean grade, weighing 250-300 g, were provided by Experimental Animal Department of China Medical University. All rats were randomly divided into sham-operation group, ischemia/reperfusion group and treatment group with 10 in each group. The main reagents were detailed as the follows: 100 g/L chloral hydrate, 0.5 mL CGRP (2 mg/L, Sigma Company, USA), and NGF (1× 106 U/L, 0.5 mL, Siweite Company, Dalian). METHODS: The experiment was carried out in the Department of Neurobiology, Basic Medical College of China Medical University from February to July 2005. Rat models of middle cerebral artery occlusion were established by method of occlusion, 2 hours after that rats were anesthetized and the thread was slightly drawn out for 10 mm under direct staring to perform reperfusion. Rats in the ischemia/reperfusion group received intraperitoneal injection of 1 mL saline via the abdomen at two hours later, while rats in the treatment group at 2 hours later received intraperitoneal injection of 2 mg/L CGRP (0.5 mL) and 1×106 U/L NGF (0.5 mL) once a day for 10 successive days. First administration was accomplished within 15 minutes after ischemia/reperfusion. Rats in the sham-operation group were separated of the vessels without occlusion or administration. The neural function was evaluated with Zea Longa 5-grade scale. Animals with the score of one, two and three points received Morris water-maze test to measure searching time on platform (omitting platform-escaping latency). Meanwhile, leaning and memory abilities of animals were reflected through testing times of passing through platform per minute. MAIN OUTCOME MEASURES: Experimental results of omitting platform-escaping latency and spatial probe. RESULTS: Three and two rats in the ischemia/reperfusion group and treatment group respectively were not in accordance with the criteria in the process, and the rest were involved in the final analysis. ① Comparisons of platform-escaping latency during Morris water-maze test in all the three groups: Ten days after modeling, the platform-escaping latency in the ischemia/reperfusion group was obviously longer than that in sham-operation group (P < 0.01), and was significantly shorter than that in the treatment group (P < 0.01). ② Comparisons of times of passing through platform in all the three groups: Times of passing through platform were remarkably less in the ischemia/reperfusion group than those in the sham-operation group [(1.79±0.39), (4.30±0.73) times/minute, P < 0.01], and those were markedly more in the treatment group than the ischemia/reperfusion group [(3.16±1.03), (1.79±0.39) times/minute, P < 0.01]. CONCLUSION: CGRP and NGF are capable of ameliorating the abilities of spatial learning and memory in MCAO rats, which indicates that CGRP and NGF can protect ischemic neurons.     

Low serum levels of nerve growth factor in diabetic neuropathy

Several structural and functional similarities between nerve growth factor and insulin have been described. Diabetes mellitus, a disease with absolute or relative deficiency of insulin is frequently associated with peripheral neuropathy whose physiopathological mechanisms are obscure. In this study, we measured serum levels of NGF in 18 patients with diabetic neuropathy and 9 healthy controls; patients with diabetic neuropathy had lower levels of NGF than controls (p less than 0.01). When patients were separated in two groups according to degree of impairment of motor nerve conduction velocity, those with more than 10% of impairment, had lower levels of NGF than those with less than 10% of impairment, or controls. It was found a correlation between NGF levels and decrease of motor nerve conduction velocity; then, diabetic neuropathy seems to be associated to low serum levels of NGF, pointing out a possible role of NGF in the pathology of diabetic neuropathy.