Strain comparison of synaptic density in hippocampal CA1 of aged rats

Synaptic density in hippocampal CA1 stratum radiatum was studied in two different strains of rat at 3 and 24-28 months of age. Neither Fischer 344 nor Sprague-Dawley rodents showed any age-related loss of synapses. These data support the contention that synapse loss with age is not a generalized phenomenon in the mammalian CNS.     

脑缺血大鼠大脑皮质NMDA受体的早期表达

目的　探讨脑缺血和缺血再灌注早期大脑皮质NMDA受体的变化规律。方法　健康雄性SD大鼠 4 8只 ,随机分为 6组 :假手术对照组、单纯脑缺血 1 5min、2 0min和 30min组及脑缺血 1 5min再灌流 30min和 2 4h组 ;4血管脑缺血动物模型 ;连续冰冻冠状切片观察 ,NR1 免疫组化染色特异性地显著NMDA受体的变化 ,图象分析及计算阳性单位PU值。结果　①单纯脑缺血各组PU值分别为 7 5 5± 1 81、6 91± 2 5 3和 6 0 9± 1 5 0 ,与对照组PU值 9 0 4± 1 5 7相比呈下降趋势 (P≤ 0 0 5 ) ;②再灌流 30min和 2 4h组PU值分别为 5 76± 2 2 4和 4 73± 1 34,与对照组PU值相比明显减少 36 2 9%～ 4 7 6 8% ,有统计学意义(P <0 0 5 ) ;③再灌流 0min、30min和 2 4h组两两比较 ,除 2 4h和 0min组相比NR1 阳性反应物减少有统计学意义 (P <0 0 5 )外 ,其它组别间NMDA受体下降的变化无显著性差异 (P >0 0 5 )。结论　脑缺血和缺血再灌流早期NMDA受体都存在下行调节 ,这种调节可能是一种保护性作用     

Synaptic remodelling and astrocytic hypertrophy in rat cerebral cortex from early to late adulthood

Ultrastructural observation of the molecular layer of the parietal cortex of rats, aged 3, 6, 10 and 17 months, revealed various atypical synaptic profiles besides typical synapses. The atypical synapses were frequently in the vacinity of hypertrophied astrocytic profiles, and were sometimes completely surrounded by astrocytic processes. The presynaptic terminal contained either no vesicles or a few small distored vesicles. Vacant postynaptic terminals were occasionally seen. The total surface area of astrocytic profiles and the numbers of atypical synapses increased significantly between 3 and 10 months. The astrocytic acquistion of degerating terminals was repeatedly observed over this period. Since there was no decrease in total synaptic number at this age, the astrocytic phenomenon may represent a stage in a continuous cycle of synaptic loss and replacement in the normal brain. By 17 months, when total synapse numbers decrease, synaptic replacement may be less than optimal.     

大鼠睁眼前初级视皮层2/3层锥体神经元突触自身稳态可塑性的变化特征

目的：通过对Wistar大鼠睁眼前初级视皮层2/3层锥体神经元突触AMPA（α-氨基-3-羧基-5-甲基异恶唑-4-丙酸）介导的微小兴奋性突触后电流 (mEPSCs)的测定分析,研究突触自身稳态可塑性在生后早期初级视皮层的作用特点。方法: 采用红外可视膜片钳技术全细胞模式记录生后4-11(d)（P4-11）Wistar大鼠初级视皮层脑片2/3层锥体神经元AMPA介导的mEPSCs,钳制电位-70 mV。人工脑脊液中加入河豚毒素（TTX）、荷包牡丹碱（BMI）及2-氨基-5-磷酸基戊酸（AP-5）分离出AMPA介导的mEPSCs,加入阻断剂6-氰基-7-硝基喹喔啉-2,3二酮 (CNQX）可消除mEPSCs。使用Clampfit 9.0进行数据分析。结果: P4至P11,大鼠初级视皮层2/3层锥体神经元AMPA介导的mEPSCs的波幅呈现上升趋势,频率自P7至P11逐渐增加,上升时间常数及下降时间常数均呈缩短趋势,以下降时间常数变化为著。P4至P7可见“单通道样”电流形态。结论: 在大鼠睁眼前初级视皮层2/3层锥体神经元亦存在突触自身稳态可塑性调节机制,其作用特点不同于睁眼后。     

The cerebral cortex of the reeler mouse embryo

Summary The cerebral cortex of reeler (rl/rl) and control (rl/+) embryos has been examined at embryonic day 14 (E0=day of the plug). At this early stage, the cells of the cortical plate in reeler are characteristically maloriented when compared to the controls but, despite this malorientation, they assume a normal differentiation; in particular the regions of contact between the cells of the cortical plate are not different from the controls. The marginal zone and the subcortical plate of reeler are less well delimited than in normal fetuses, yet each of these layers contains the same contingent of cells and fibers as the normal embryos. In particular an early afferent fiber system is visualized in reeler and shows the same characteristics as in normal embryos: weak osmiophily, presence of dense core vesicles and of multilocular dense vacuoles, formation of asymmetric synapses in the marginal zone. The nature of these fibers is unknown but it is suggested that they could correspond to the aminergic system described in rats at the same developmental stage.The observations reported, though compatible with the hypothesis that the reeler gene acts upon a cell recognition-adhesion phenomenon between CP cells, do not provide a positive evidence for it and do not exclude other explanations.Aspirant au Fonds National de la Recherche Scientifique de Belgique     

Stability of synaptic density and spine volume in dentate gyrus of aged rats

The number of synapses per unit volume and per granule cell and the size of dendritic spines were studied in the dentate gyrus of Sprague-Dawley rats 6, 24, and 30 months of age. Neither synaptic density nor mean spine volume showed any age-related trends. An increase in granule cell packing density at 24 months and concomitant stability of the height of the granule cell layer is consistent with the idea that postnatal generation of granule cells may continue late into life. Possible explanations for the discrepancies in the literature regarding synaptic loss in this area include differences in morphometric techniques, age of animals used, regional differences within dentate gyrus, and sampling variability. Generalized synapse loss in the senescent rodent brain remains to be established.     

大鼠脑皮质星形胶质细胞体外培养方法的改进

目的改进大鼠脑皮质星形胶质细胞体外培养方法,获得纯度较高的大鼠脑皮质星形胶质细胞。方法取出生后1d内SD大鼠大脑皮质,用机械吹打法使细胞分散制成初细胞悬液,10μm尼龙膜过滤除去成纤维细胞后接种。待7d细胞铺满瓶底后,＂十＂字形震荡培养液5min后传代接种。传代2次后行GFAP免疫组化染色鉴定。结果通过微孔尼龙膜过滤和传代前＂十＂字形震荡培养液等操作可以得到形态典型、纯度较高的星形胶质细胞。通过纯度计算可得离体培养的星形胶质细胞的纯度平均值为95.49%（n=6）。结论改进的星形胶质细胞体外培养方法,降低了实验操作难度,方法稳定有效,得到的星形胶质细胞纯度较高。     

活性氧清除剂对缺氧所致大鼠大脑皮层细胞产生脂质过氧化物的影响

对缺氧所致的大鼠大脑皮层细胞选用不同的活性氧清除剂观察其对脂质过氧化物的影响。苯甲酸钠可抑制脑细胞脂质过氧化，使脂质过氧化物生成减少；超氧化物歧化酶、过氧化氢酶和谷胱甘肽过氧化物酶对细胞脂质过氧化亦有不同程度的抑制作用，其中超氧化物歧化酶作用较强，谷胱甘肽过氧化物酶次之，过氧化氢酶作用较弱。结果提示缺氧可引起脑细胞活性氧生成增加。拮抗ＯＨ·或清除Ｏ和Ｈ＿（２）Ｏ＿（２），减弱ＯＨ·的效应均可降低细胞脂质过氧化物的生成。     

Efflux of phenylalanine and tryptophan from cerebral cortex slices of adult and 7-day-old rats

An equation of two exponential terms was found to adequately describe the efflux of phenylalanine and tryptophan from cerebral cortex slices of adult and 7-day-old rats. These exponential terms described two forms (components) of efflux taking place at different rates. The fast component of efflux was more prominent in the slices from young rats than in those from adults. In both age groups the contribution of the fast component increased with an increasing amino acid concentration in the superfusate, but there were no changes in the rate constants. The rate constants of the fast components were equal in all experimental conditions in both age groups. The rate constants for the slow components of both amino acids were lower in the slices from adult rats than in those from young rats. The reason for efflux occurring at two different rates is discussed. The fast component probably consisted of the amino acid originating from the extracellular space of the slices and of the intracellular amino acid released by exchange. The slow component consisted of the amino acid released from the cells by other mechanisms, e.g. by diffusion through the membranes or by some active efflux processes. The cerebral cortex slices from adult rats have greater ability to concentrate aromatic amino acids than the slices from young rats. This may partly be dependent on the more effective influx and partly on the slower efflux of amino acids in the slices from adults.     

Canal-neck interaction in vestibular neurons of the cat's cerebral cortex

Summary Interaction of semicircular canal and neck proprioceptive inputs was studied in the cerebral cortex of awake, intact cats. Neuronal responses were recorded extracellularly in the anterior suprasylvian gyrus of the left hemisphere. Stimulations consisted of horizontal rotations in the dark applied as sinusoids or position ramps. There were three stimulus conditions: (1) Pure canal stimulation; rotation of whole body. (2) Pure neck stimulation; rotation of trunk about stationary head. (3) Canalneck interaction; rotation of head about stationary trunk.(1) We recorded 105 neurons with either Type I or Type II canal response. These showed often pronounced non-linearities such as a clear firing increase upon rotation in the on-direction and hardly any decrease in the opposite direction. The responses reflected mostly angular velocity, but angular position signals were also obtained. (2) In 79 neurons, either Type I or Type II neck responses were obtained. They coded either angular velocity, velocity plus position, or position. (3) Canal-neck convergence was found in 67 of 88 neurons tested. In the majority of neurons, interaction was dantagonistic in the sense that the canal and neck responses tended to cancel each other during rotation of the head about the stationary trunk. These neurons could signal trunk rotation in space rather than head in space or head relative to trunk. Most of the remaining neurons showed a synergistic interaction such that the response upon head rotation was enhanced as compared to whole body or trunk rotation. These neurons might be involved in the dual task of monitoring head rotation in space and relative to trunk. Interaction was compatible with linear summation of canal and neck inputs in 70% of the neurons. In part of these, however, the assumption had to be made that the interaction had taken place already at some stage prior to the cortical neurons investigated. The response characteristics of cortical canal neurons are discussed in comparison to vestibular nuclear neurons. Furthermore, parallels are drawn between the observed canal-neck interactions in the cortical neurons and (i) interactions of canal and neck dependent postural reflexes in the decerebrate cat, and (ii) interactions of canal and neck induced turning sensations in man.     

An attempt to assess the effects of monocular deprivation and strabismus on synaptic efficiency in the kitten's visual cortex

Summary The relative effectiveness of the two eyes in exciting cells in the visual cortex was assessed, using both natural stimulation and electrical stimulation of the optic discs. It is argued that supramaximal electrical stimulation of the optic nerve could possibly reveal subliminal synaptic inputs even after monocular deprivation or artificial strabismus has caused a loss of natural input from that eye, if such silent synaptic input still survives. However, in kittens monocularly deprived for various periods of time or made artificially strabismic, there was usually excellent agreement between the relative visual excitability in the two eyes and their relative electrical excitability. In one animal, monocularly deprived continuously until 23 weeks of age, we examined the effect of reversibly turning off signals from the normal eye by pressure blinding. There was no evidence of a very rapid return of sensitivity to either electrical or natural stimulation of the deprived eye.Royal Society Locke Research FellowOn leave from The Neurobiology Unit, The Hebrew University of Jerusalem, Jerusalem, Israel     

Exchange and efflux of tryptophan from superfused cerebral cortex slices

Summary The efflux and exchange of L-tryptophan (Trp) from rat cerebral cortex slices were studied in a superfusion system. The substrate specificity of Trp exchange was assessed by measuring the stimulation of [³H]Trp exit provoked by other extracellular amino acids. Large neutral amino acids were the most potent, but also glutamic acid, lysine and glycine had some effect. The stimulation caused by extracellular Trp and phenylalanine persisted also at 0 ° C though severalfold attenuated. Only intracellular histidine provoked slight inhibition of [³H]Trp efflux and intracellular Trp, phenylalanine and lysine had a small stimulatory effect. The results suggest an involvement of carrier-mediated processes in the exchange and efflux of Trp. The substrate specificities of the exchange and efflux are not apparently identical.     

Loss of dendritic spines in aging cerebral cortex

Summary Previous work has shown that the dendritic spines of pyramidal neurons of the cerebral cortex are sensitive to a wide variety of environmental and surgical manipulations. The present study shows that the normal aging process also affects these spines. The spines were studied with the light microscope in Golgi preparations from rats ranging in age from 3 to 29.5 months. Visible spines were counted on either 25 or 50 segments of the basal dendrites, apical dendrites, oblique branches, and terminal tufts of layer V pyramidal cells in area 17. A progressive loss of spines occurred at each of these loci. The smallest observed spine loss (24%) occurred on the dendrites of the terminal tuft, and the largest (40%) on the oblique branches. Age-related spine loss appears to affect all animals, and for animals of any one age the overall loss is similar. However, the cell-to-cell variability within an individual animal is pronounced, some cells with high spine densities being present at every age examined. As a general rule, there is a positive relationship between visible spine density along the apical dendrite as it traverses layer IV and the thickness of the dendrite. With advancing age, the relatively thick dendrites decrease in number so that the thinner dendrites make up an increasingly larger proportion of the total apical dendrite population. Questions that remain for the future include the genesis of the spine loss, its relation to other aging changes, and its functional significance for the neuron.Supported by United States Public Health Service Program Project Grant HDO-5796-03 and Research Grant NB-07016     

大鼠脑缺血后突触体素与突触密度的关系

目的：观察脑缺血后,大脑顶叶皮质突触体素的表达与突触密度的关系,为脑缺血后监测突触密度的变化提供了一个间接方法。方法：采用大鼠脑缺血模型,用免疫组化及电镜方法。结果：脑缺血后,随缺血时间的延长,突触体素的表达逐渐减少;神经毡内突触数目逐渐减少。结论：脑缺血后,随缺血时间延长,突触体素表达减少,神经毡内突触数目逐渐减少,二者之间呈正相关,说明突触体素可作为监测突触密度的间接指标。     

Electrophysiological investigations on the projections from the cerebral cortex to the vermal posterior lobe of the cerebellum

Summary The following cerebrocortical areas have been electrically stimulated in cats under Nembutal anaesthesia: forelimb and hindlimb areas of the primary sensorimotor cortex, primary and secondary acoustic areas and visual area. Stimulation of these regions evokes in the vermal portion of lobuli VI and VII of the cerebellum potentials at a short latency (2.8–3.5 ms) and at a longer latency (12–22 ms), which have been identified as due to mossy and climbing fibre inputs respectively. Each point of the cerebellar cortex receives usually projections by some and never by all the stimulated cerebrocortical areas. The different cortical regions don't project predominantly to separate parts of the cerebellar cortex, but they project in an apparently random manner with a patchy arrangement.In the anterior lobe we have confirmed the known somatotopy from the primary sensorimotor cortex and we have found no projections from the other cerebrocortical areas.This work has been performed in part with a grant given by the Consiglio Nazionale delle Ricerche to the E.U.L.O., Brescia     

碘过量对大鼠子代大脑锥体细胞的形态学影响

目的观察不同碘水平对仔鼠大脑皮质发育的形态学影响。方法断乳后1个月大鼠饮用不同浓度的碘水,饲养3个月后雌雄合笼,取第2代60日龄仔鼠,测量血清甲状腺激素值,测量全脑重量,观察大脑皮质内锥体细胞层锥体细胞的形态学改变(苏木精-伊红染色和镀银染色)。结果各碘过量组甲状腺激素水平呈下降趋势,100HI组呈明显甲低状态;各高碘组仔鼠大脑皮质神经元排列分层及细胞形态与适碘组相比,未见明显改变(P<0.05)。结论大鼠对碘摄入量的增高有较强的耐受性,本实验各碘过量组中均未见仔鼠大脑皮质锥体细胞产生明显的形态改变。但过高碘摄入时(100HI组)表现为甲状腺功能低下,是否会引起仔鼠大脑皮质神经元的功能改变,还有待于进一步实验研究。     

The size and curvature of synapses in the cerebellar cortex of the cat

Summary At the supra Purkinje layer and the subpial level in the molecular layer of lobules V and VI of the cerebellar cortex of the cat, synaptic profiles were measured in ultrathin serial sections treated with either osmium tetroxide (OsO₄) or ethanolic phosphotungstic acid (E-PTA). From trace and chord lengths of the intercepts of synaptic profiles the curvature and the mean caliper diameter of the synapse was calculated. In OsO₄-material the curvature of synapses yielded an average angle of about 47 degrees and about 36 degrees in E-PTA material.Although these values are contrary to the assumption of a flat disc, which is commonly required in stereological procedures to estimate caliper diameter, the effect of the curvature on the estimation of the mean caliper diameter is limited. This is shown by serial reconstruction analysis of the largest diameter of synapses from maximal arc and chord length measurements at the subpial and supra Purkinje level. The results provide quantitative data concerning synaptic size, curvature and the frequency of intercepts per synapse at the subpial and supra Purkinje level in the cerebellar cortex in OsO₄ and E-PTA material. In addition the advantages and disadvantages of E-PTA and osmiumtetroxide staining in quantitative analysis are discussed.     

高铁对大鼠大脑皮层二价金属转运蛋白1表达的影响

目的 探讨在脑铁代谢中发挥重要生理作用的二价金属转运蛋白1(DMT1)的表达及其调控机制.方法 大鼠(n=6)侧脑室注射右旋糖酐铁3d和7d后,采用铁组织化学法检测脑内铁含量的变化,免疫组织化学技术检测大脑皮层中DMT1的两种亚型,即DMT1(+IRE)和DMT1(-IRE)蛋白表达的变化.结果 铁组织化学染色结果显示,大鼠侧脑室注射右旋糖酐铁500μg/(只·d)7d后,大脑皮层中二价铁和三价铁均显著增高.同时,免疫组织化学结果表明,与对照组相比,脑内达高铁状态时大脑皮层DMT1(+IRE)蛋白表达显著升高,而DMT1(-IRE)蛋白表达无显著变化.结论 在大鼠大脑皮层中,DMT1(+IRE)蛋白对铁水平的升高更为敏感,其表达与脑铁水平(尤其是二价铁)呈正相关.高铁对脑内不同区域内不同亚型DMT1表达的影响存在特异性.     

Topographical projections from the cerebral cortex to the nucleus of the solitary tract in the cat

Summary The distribution of cerebral cortical neurons sending projection fibers to the nucleus of the solitary tract (NST), and the topographical distribution of axon terminals of cortico-NST fibers within the NST were examined in the cat by two sets of experiments with horseradish peroxidase (HRP) and HRP conjugated with wheat germ agglutinin (WGA-HRP). First, HRP was injected into the NST. In the cerebral cortex of these cats, neuronal cell bodies were labeled retrogradely in the deep pyramidal cell layer (layer V): After HRP injection centered on the rostral or middle part of the NST, HRP-labeled neuronal cell bodies were distributed mainly in the orbital gyrus and caudal part of the infralimbic cortex, and additionally in the rostral part of the anterior sylvian gyrus. After HRP injection centered on the caudal part of the NST, labeled neuronal cell bodies were seen mainly in the caudoventral part of the infralimbic cortex, and additionally in the orbital gyrus, posterior sigmoid gyrus and rostral part of the anterior sylvian gyrus. The labeling in the infralimbic cortex, orbital gyrus and anterior sylvian gyrus was bilateral with a predominantly ipsilateral distribution, while that in the posterior sigmoid gyrus was bilateral with a clear-cut contralateral dominance. In the second set of experiments, WGA-HRP was injected into the cerebral cortical regions where neuronal cell bodies had been retrogradely labeled with HRP injected into the NST: After WGA-HRP injection into the orbital gyrus, presumed axon terminals in the NST were labeled in the rostral two thirds of the nucleus bilaterally with an ipsilateral predominance. After WGA-HRP injection into the rostral part of the anterior sylvian gyrus, a moderate number of presumed axon terminals were labeled throughout the whole rostrocaudal extent of the NST bilaterally with a slight ipsilateral dominance. After WGA-HRP injection into the middle and caudal parts of the anterior sylvian gyrus, no labeling was found in the NST. After WGA-HRP injection into the caudal part of the infralimbic cortex, presumed terminal labeling in the NST was seen throughout the whole rostrocaudal extent of the nucleus bilaterally with a dominant ipsilateral distribution. After WGA-HRP injection into the posterior sigmoid gyrus, however, no terminal labeling was found in the NST. The results indicate that cortico-NST fibers from the orbital gyrus terminate in the rostral two thirds of the NST, while those from the infralimbic cortex and the rostral part of the anterior sylvian gyrus project to the whole rostrocaudal extent of the NST.     

An electron microscopic study of dendritic degeneration in the cerebral cortex resulting from laminar lesions

Summary The morphological characteristics of dendrites in layers of the cerebral cortex above laminar lesions induced by ionizing particle irradiation have been studied in the striate field of rat at various survival times. Within two weeks following irradiation an increasing number of dendrites display unusual alterations inferred to be signs of degeneration.Degenerating dendrites can be characterized by a dense cytoplasmic matrix, disruption of mitochondria, presence of dense bodies, irregular outline and a marked alteration of the plasmalemma in its dimensions and staining properties. Some degenerating dendrites possess a large accumulation of dense subsynaptic material and are contacted by synapses with enlarged and altered synaptic clefts. A few dendrites contain extensive membranous whorls. Engulfment by reactive astrocyte processes is a common feature and often includes the presynaptic axonal knob, but only the degenerating dendrite has been observed within glial cytoplasm. The inference that the majority of degenerating dendrites in this material are apical dendrites of pyramidal cells suggests that either shaft synapses are common for these cells, protuberances may retract during degeneration, or spines are lost due to loss of afferent terminals.Supported by research grants from the United States Public Health Service, NB-4578 and NB-6594.