金黄地鼠视皮层通过胼胝体顺行和逆行激活的神经元的电活动和分布

用细胞外记录技术研究了金黄地鼠一侧视皮层神经元对电刺激另一侧相应部位的反应及其对视觉刺激反应的特点。(1)在17—18a 交界区大多数(78%)细胞能被电刺激对侧相应点所驱动。在17区内部,被驱动细胞数随离开17—18a 交界距离增加而减少。(2)按对电刺激的反应形式,记录的细胞可分为四类:a.逆行驱动细胞,占17—18a 交界区记录细胞数的20%;b.顺行驱动细胞,占52%中;c.自发发放因电刺激而减少或完全停止的细胞,占6%,d.其余细胞(22%)对电刺激没有可察觉的反应。(3)在17—18a 交界,除了Ⅰ层以外的各层都可记录到顺行驱动细胞,而逆行驱动细胞则主要集中在Ⅲ及Ⅴ层。(4)17—18a 交界细胞感受野(RF)多位于垂直中线附近的对侧视野内,有些 RF 跨越中线,其边界延伸到同侧约10°处。(5)逆行驱动细胞包括刁和 Blakemore 以前在视皮层中记录到的所有细胞类型和各种程度的眼优势,但单眼细胞的比例增加,非对称式 RF 和中心对称式的给-撤型 RF 的比例有所减少。     

胼胝体输入对猫17/18区交界神经元反应强度的影响

用微机控制的以一定速度移动的亮棒或暗棒作为视觉刺激,在视皮层一侧施加GABA或其拮抗剂荷苞牡丹碱(Bicuculline,简写为Bicu),在对侧皮层17/18区交界附近记录加药前后单细胞的视觉反应.结果表明,对侧施加GABA后有52.1%细胞反应减少,22.5%细胞反应增加;对侧施加Bicu后有44.9%细胞反应增加,23.2%细胞反应减少;对两种药物均无反应的细胞不足10%.实验中受胼胝体神经元影响的对侧细胞的百分比明显高于以往用其它方法所得到的结果.本文对实验结果的可靠性和意义做了讨论.     

躯体感觉Ⅱ区皮层内微刺激对猕猴回避性操作式条件反射和针刺镇痛的影响

在七只清醒、可以活动的猕猴上观察了皮层内刺激 S_Ⅱ区对外周痛阈和针刺镇痛的影响,其结果如下:(1)在73次皮层内刺激的实验中有72次引起对侧相应皮肤感受野的痛阈变化,其中54次痛阈明显升高。痛阈升高的效应在停止刺激后常持续0.5—3min。较浅层的刺激,痛阈升高比较明显;不同刺激强度引起的痛阈升高的程度也不相同。(2)一般皮层内刺激 S_Ⅱ区也可导致同侧相应皮肤感受野痛阈升高,但不如对侧痛阈升高明显。(3)皮层内刺激 S_Ⅱ区时,非感受野痛阈几乎没有任何改变。(4)S_Ⅱ区皮层内刺激可增强针刺镇痛效应。     

大脑皮层对于对侧皮层单个刺激的重复反应

用单个电刺激直接刺激不麻醉兔的大脑皮层,在对側皮层相应区域引起的反应包含一串頻率10—20次/秒,以表面負电位为主的重复反应。直接刺激胼胝体也可以在两侧皮层引起相同的重复反应,然而两侧之間并不同步。在切断胼胝体后这种反应仍能出現,但将胼胝体和丘脑都沿中綫切开,反应就消失不見。将一側丘脑吸去,保留胼胝体,不論刺激那一侧皮层,都只在丘脑存留侧的皮层才能得到重复反应。从这些結果来看,刺激一側皮层可以通过胼胝体和丘脑,激发另一侧皮层和丘脑之間线路的活动而引起重复反应。     

体感Ⅰ区和Ⅱ区同时皮层内微刺激对猕猴外周皮肤痛阈的影响

本实验以皮肤伤害性刺激引起的回避性操怍式条件反射作为外周皮肤痛指标,在七只清醒、可以活动的猕猴身上观察了同时皮层内刺激SⅠ区和SⅡ区对外周痛阈的影响,其结果如下:(1)在单独刺激SⅠ区或SⅡ区后肢代表区观察到对侧后肢皮肤相应感受野痛阈明显升高后,同时刺激SⅠ及SⅡ区的47次实验中,有31次可见痛阈比单独刺激SⅠ或SⅡ区痛阈进一步有不同程度的升高;13次其痛阈未见进一步升高;3次其痛阈反而下降。(2)单独刺激SⅠ区后肢代表区,对同侧外周皮肤感受野痛阐没有影响,单独刺激SⅡ区的后肢代表区,则可使同侧相应外周感受野痛阈明显升高,而同时刺激SⅠ区和SⅡ区的8次实验中有7次发现同侧肢体皮肤感受野痛阈也进一步升高。(3)10次单独刺激SⅠ或SⅡ区,均未见非感受野皮肤痛阈明显改变,同时刺激SⅠ和SⅡ区也未见其痛阈有明显影响。相反10次同时刺激SⅠ和SⅡ区的手代表区也未发现对后肢皮肤痛阈有明显影响。结果提示:两个体感区对上行痛觉信息的相互间的调制作用主要表现为加强对外周痛阈的抑制作用。     

Wistar大鼠运动皮层代表区的微刺激测定

在１５例氯胺酮麻醉的Ｗｉｓｔａｒ大鼠利用皮层内微刺激技术测定了躯体的运动皮层代表区。电刺激为３５０Ｈｚ的阴极串脉冲,电流最大值限为８０μＡ。结果表明大多数皮层点诱发对侧肌肉反应。虽然代表区的大小有很大个体差异,分区的相对位置是恒定的。但在分区内部未见分域排列。部分大鼠存在前部前肢区,但无一例发现前部后肢区。比较文献结果提示Ｗｉｓｔａｒ大鼠的运动皮层的分化程度比Ｌｏｎｇ－Ｅｖａｎｓ黑顶鼠低。     

参与不同难度数字计算的脑区——脑功能磁共振成像研究

本研究用功能磁共振成像技术观察了人脑进行不同难度数字加减计算时的脑区激活情况,并探讨大脑皮层和皮层下结构在数字计算中的作用.用Siemens 1.5 Tesla磁共振机对16名右利手健康志愿者进行简单及复杂数字加减任务的fMRI扫描.实验采用组块设计.刺激任务分为简单加减计算任务、复杂加减计算任务和基线任务.用SPM99软件进行数据分析和脑功能区定位.分别比较同一任务各个脑区平均激活强度和同一脑区在两种任务中的激活强度.结果显示,简单及复杂加减计算激活的被试者的脑区基本相同,激活的皮层区主要见于额叶、顶叶、枕叶、扣带回、丘脑及小脑;简单及复杂加减计算激活的皮层下结构包括两侧尾状核、左纹状体边缘区等基底核结构和丘脑.在简单及复杂计算中,纹状体与皮质结构(额叶、顶叶)间激活强度均无显著性差异.简单计算与复杂计算比较,右顶叶,在复杂任务时出现激活,在简单任务时未出现激活.上述结果提示,完成数字计算任务的脑区除了额叶、顶叶、扣带回等皮层结构外,大脑皮层下的一些结构如纹状体、纹状体边缘区,也是参与数字计算的重要部位.皮层下结构纹状体和优势半球的纹状体边缘区参与了数字工作记忆,可能是进行数字计算神经环路的重要组成部位.右项叶(缘上回)只在复杂任务出现激活,该区可能是视空间记忆和加工的重要部位.     

刺激兔丘脑不同核团和胼胝体引起的膈神经放电效应

实验在33例清醒、肌肉麻痹和切断双侧迷走神经的家兔上进行,观察了刺激丘脑不同核团(VIL,VL,VPM 和 MI)和胼胝体纤维以激活皮层时膈神经的放电效应。当在吸气相(膈神经放电时)给予上述核团及胼胝体纤维电脉冲刺激,可使膈神经放电短暂抑制,随后的呼气相缩短、吸气相提前出现。如果在呼气相刺激上述核团,也能使该呼气时相缩短,随后的吸气时相提前出现。当在皮层接受 VL 投射的局部区域给予回苏灵后,再刺激 VL,皮层诱发电位增大,除使原先的膈神经放电效应更为明显外,还可在呼气相刺激时引起膈神经即刻的短暂放电。以上实验结果提示,当用回苏灵使皮层活动加强后,刺激丘脑 VL 引起的膈神经放电效应明显增强。损毁红核或切断皮层下行传导束但保留皮层脊髓束后,刺激丘脑引起的膈神经放电效应均不受影响,表明传入冲动激活皮层后引起的膈神经放电效应可能主要经皮层脊髓束下传,而皮层红核脊髓束不起重要作用。     

C类纤维传入诱发体感皮层电反应的脊髓上传通路

实验用猫,在氯醛糖和三碘季铵酚处理下进行。以强电脉冲刺激腓浅神经,结合极化电流阻滞A类纤维的传入后,选择性引起C类纤维传入时,在对侧大脑皮层体感Ⅰ区记录到特异的C类纤维皮层诱发电位(G-CEP)。观察到损毁脊髓胸11节段对侧腹外侧索后,C-CEP的幅值明显衰减;损毁同侧背索后,G-CEP的幅值也明显衰减;保留同侧背索,损毁脊髓其他部份后,C-CEP仍出现,但幅值变小;同时损毁上述两索后,C-CEP完全消失。提示C类纤维传入诱发C-CEP的脊髓上传通路位于同侧背索和对侧腹外侧索。     

刺激兔皮层感觉运动区引起的膈神经放电效应

在53例清醒、肌肉麻痹、切断迷走神经的家兔,刺激对侧皮层感觉运动区引起膈神经上的放电效应包括两种不同成分。第一效应指紧接刺激发生的放电变化。在呼气相刺激时,第一效应表现为短暂的放电;在吸气相刺激时,则表现为放电的抑制。士的宁刺激较易在呼气相引起第一效应,电刺激较易在吸气相引起第一效应。在 C_2切断同侧背外侧束可使第一效应消失,提示第一效应经皮层脊髓束和皮层红核脊髓束下行。第二效应指刺激后呼吸周期放电的变化。不论是在呼气相或吸气相刺激,第二效应均表现为吸气放电的提前出现、吸气时程和呼气时程的缩短。同时记录延髓孤束区单位放电与膈神经放电时,两者放电均有表现一致的第二效应。在 C_2切断同侧背外侧束,不影响第二效应的出现;完全切断同侧脊髓,则膈神经放电消失,但不影响孤東区的第二效应。以上结果说明,皮层控制膈运动神经元有两条途径,一条是皮层直接下达脊髓的途径,另一条是间接通过脑干呼吸中枢下达脊髓的途径;皮层直接下达脊髓的通路,既可兴奋也可抑制膈运动神经元的活动。     

Enhanced neurogenesis and cell migration following focal ischemia and peripheral stimulation in mice

Peripheral stimulation and physical therapy can promote neurovascular plasticity and functional recovery after CNS disorders such as ischemic stroke. Using a rodent model of whisker-barrel cortex stroke, we have previously demonstrated that whisker activity promotes angiogenesis in the penumbra of the ischemic barrel cortex. This study explored the potential of increased peripheral activity to promote neurogenesis and neural progenitor migration toward the ischemic barrel cortex. Three days after focal barrel cortex ischemia in adult mice, whiskers were manually stimulated (15 min x 3 times/day) to enhance afferent signals to the ischemic barrel cortex. 5-Bromo-2'-deoxyuridine (BrdU, i.p.) was administered once daily to label newborn cells. At 14 days after stroke, whisker stimulation significantly increased vascular endothelial growth factor and stromal-derived factor-1 expression in the penumbra. The whisker stimulation animals showed increased doublecortin (DCX) positive and DCX/BrdU-positive cells in the ipsilateral corpus of the white matter but no increase in BrdU-positive cells in the subventricular zone, suggesting a selective effect on neuroblast migration. Neurogenesis indicated by neuronal nuclear protein and BrdU double staining was also enhanced by whisker stimulation in the penumbra at 30 days after stroke. Local cerebral blood flow was better recovered in mice that received whisker stimulation. It is suggested that the enriched microenvironment created by specific peripheral stimulation increases regenerative responses in the postischemic brain and may benefit long-term functional recovery from ischemic stroke.     

Increased synaptophysin expression through whisker stimulation in rat

1. Synaptophysin is responsible for the cycling of the synaptic vesicles containing the neurotransmitter, and it can be phosphorylated.2. This study examined whether repeated whisker stimulation alters the expression of synaptophysin mRNA in the rat barrel cortex, and found induced expression of synaptophysin mRNA in the contralateral barrel cortex compared to that in the ipsilateral hemisphere.3. This result suggests that synaptophysin is involved in the modulation of the synaptic plasticity.     

Cortical potentials evoked by mechanical stimulation of different number of vibrissae of the rat

Distribution maps of cortical potentials evoked by mechanical stimulation of different number of contralateral vibrissae were studied. It was found that stimulation of all the contralateral vibrissae led to more extensive activation than the barrel field in the somatosensory cortex. The activation was most widespread when all the vibrissae were synchronously deflected. With reduction of the number of synchronously stimulated whiskers the activated cortical area did not decrease in parallel. Deflection of only a few whiskers activated significantly smaller cortical areas.     

在体神经元胞外记录用于大脑皮层可塑性研究

神经元网络可塑性是大脑学习和记忆功能的基础,可塑性的变化也是某些脑功能疾病的成因。研究大脑皮层可塑性不仅可以为认识可塑性机制提供基本方法,也可对自然衰老过程和神经退行性疾病的病理过程进行观测,进而可以为评价抗衰老药物和治疗神经退行性疾病提供新方法。本文基于经典的大鼠胡须配对模型建立了一套实验方案,通过在体细胞外记录实验的数据分析,比较修剪胡须后相同时间内神经元感受野不对称变化程度的差异,衡量不同生理条件下大鼠体感皮层神经元网络可塑性。本文以中年和青年大鼠体感皮层神经元网络可塑性比较为例,详细介绍了实验方法中的关键技术和操作,如皮层D2功能柱的定位和D2功能柱内不同层神经元的定位等,结果和我室以前相关研究证明了此实验方案的可行性。     

Use-dependent plasticity in barrel cortex: Intrinsic signal imaging reveals functional expansion of spared whisker representation into adjacent deprived columns

We used optical imaging of intrinsic cortical signals, elicited by whisker stimulation, to define areas of activation in primary sensory cortex of normal hamsters and hamsters subjected to neonatal follicle ablation at postnatal day seven (P7). Follicle ablations were unilateral, and spared either C-row whiskers or the second whisker arc. This study was done to determine if the intrinsic cortical connectivity pattern of the barrel cortex, established during the critical period, affects the process of representational plasticity that follows whisker follicle ablation. Additionally, we tested the ability to monitor such changes in individual cortical whisker representations using intrinsic signal imaging. Stimulation of a single whisker yielded peak activation of a barrel-sized patch in the somatotopically appropriate location in normal cortex. In both row and arc-spared animals, functional representations corresponding to spared follicles were significantly stronger and more oblong than normal. The pattern of activation differed in the row-sparing and arc-sparing groups, in that the expansion was preferentially into deprived, not spared areas. Single whisker stimulation in row-spared cases preferentially activated the corresponding barrel arc, while stimulation of one whisker in arc-spared cases produced elongated activation down the barrel row. Since whisker deflection normally has a net inhibitory effect on neighboring barrels, our data suggest that intracortical inhibition fails to develop normally in deprived cortical columns. Because thalamocortical projections are not affected by follicle ablation after P7, we suggest that the effects we observed are largely cortical, not thalamocortical.     

Use-dependent plasticity in barrel cortex: intrinsic signal imaging reveals functional expansion of spared whisker representation into adjacent deprived columns

We used optical imaging of intrinsic cortical signals, elicited by whisker stimulation, to define areas of activation in primary sensory cortex of normal hamsters and hamsters subjected to neonatal follicle ablation at postnatal day seven (P7). Follicle ablations were unilateral, and spared either C-row whiskers or the second whisker arc. This study was done to determine if the intrinsic cortical connectivity pattern of the barrel cortex, established during the critical period, affects the process of representational plasticity that follows whisker follicle ablation. Additionally, we tested the ability to monitor such changes in individual cortical whisker representations using intrinsic signal imaging. Stimulation of a single whisker yielded peak activation of a barrel-sized patch in the somatotopically appropriate location in normal cortex. In both row and arc-spared animals, functional representations corresponding to spared follicles were significantly stronger and more oblong than normal. The pattern of activation differed in the row-sparing and arc-sparing groups, in that the expansion was preferentially into deprived, not spared areas. Single whisker stimulation in row-spared cases preferentially activated the corresponding barrel arc, while stimulation of one whisker in arc-spared cases produced elongated activation down the barrel row. Since whisker deflection normally has a net inhibitory effect on neighboring barrels, our data suggest that intracortical inhibition fails to develop normally in deprived cortical columns. Because thalamocortical projections are not affected by follicle ablation after P7, we suggest that the effects we observed are largely cortical, not thalamocortical.     

Widespread Activation of Barrel Cortex by Small Numbers of Neonatally Spared Whiskers

Activity-dependent plasticity in rodent whisker barrel cortex was examined by means of high-resolution 2-deoxyglucose (2-DG) with immunohistochemical double labeling. Hamsters with all but one, two, or four follicles ablated on postnatal day 7 received 2-DG injections as adults. Autoradiograms of follicle-ablated animals showed heavy activation of the entire barrel field during normal behavior, despite the missing whiskers. The intensity of 2-DG labeling was significantly reduced if the whiskers spared after follicle ablation were trimmed prior to the 2-DG injection, demonstrating that the widespread activation was driven by the spared whiskers. This widespread metabolic activation of the adult barrel field after neonatal follicle ablation was in sharp contrast to the somatotopically appropriate 2-DG labeling in barrel fields of normal adults subject to acute trimming of most whiskers, but was similar to that seen in normal adult animals with all whiskers intact. The results demonstrate large-scale plasticity of barrel circuitry following neonatal sensory deprivation, and provide a powerful functional anatomical setting to investigate underlying mechanisms     

Infrared thermal imaging of rat somatosensory cortex with whisker stimulation

The present study aims to validate the applicability of infrared (IR) thermal imaging for the study of brain function through experiments on the rat barrel cortex. Regional changes in neural activity within the brain produce alterations in local thermal equilibrium via increases in metabolic activity and blood flow. We studied the relationship between temperature change and neural activity in anesthetized rats using IR imaging to visualize stimulus-induced changes in the somatosensory cortex of the brain. Sensory stimulation of the vibrissae (whiskers) was given for 10 s using an oscillating whisker vibrator (5-mm deflection at 10, 5, and 1 Hz). The brain temperature in the observational region continued to increase significantly with whisker stimulation. The mean peak recorded temperature changes were 0.048 ± 0.028, 0.054 ± 0.036, and 0.097 ± 0.015°C at 10, 5, and 1 Hz, respectively. We also observed that the temperature increase occurred in a focal spot, radiating to encompass a larger region within the contralateral barrel cortex region during single-whisker stimulation. Whisker stimulation also produced ipsilateral cortex temperature increases, which were localized in the same region as the pial arterioles. Temperature increase in the barrel cortex was also observed in rats treated with a calcium channel blocker (nimodipine), which acts to suppress the hemodynamic response to neural activity. Thus the location and area of temperature increase were found to change in accordance with the region of neural activation. These results indicate that IR thermal imaging is viable as a functional quantitative neuroimaging technique.     

Activation of a wide-spread network of inhibitory neurons in barrel cortex

Abstract The one-to-one correspondence of whiskers to barrels in layer IV of rodent somatosensory cortex can be demonstrated by a precise match between columns of heavy 2-deoxyglucose (2DG) label in layer IV barrels and other layers which correspond to stimulated whiskers. While there is specificity of peripheral-to-central mapping, the extent to which integration and/or modulation are generated by circuitry within or interactions between the barrel-defined whisker columns is not clear. Following stimulation of selected whiskers, large cells at the layer IV-V boundary throughout the barrel field are heavily labeled by 2-deoxyglucose (2DG) at high resolution. Many of these cells are outside the barrel columns of the stimulated whiskers. Further, the number of cells labeled is not directly related to the number of activated barrel columns. These neurons are not labeled in animals anesthetized before 2DG injection and are not as heavily labeled in barrel fields of somnolent animals. Most of the heavily labeled neurons immunolabel for glutamate decarboxylase (GAD) and are presumed to be inhibitory, while a smaller number of labeled neurons, presumed to be excitatory, immunolabel for glutamate (Glu). Similar populations of large, heavily 2DG-labeled neurons are found in other cortical areas. These relatively few neurons are exceptionally active and may modulate integrative functions of cerebral cortex.     

Imaging the spatio-temporal dynamics of supragranular activity in the rat somatosensory cortex in response to stimulation of the paws

We employed voltage-sensitive dye (VSD) imaging to investigate the spatio-temporal dynamics of the responses of the supragranular somatosensory cortex to stimulation of the four paws in urethane-anesthetized rats. We obtained the following main results. (1) Stimulation of the contralateral forepaw evoked VSD responses with greater amplitude and smaller latency than stimulation of the contralateral hindpaw, and ipsilateral VSD responses had a lower amplitude and greater latency than contralateral responses. (2) While the contralateral stimulation initially activated only one focus, the ipsilateral stimulation initially activated two foci: one focus was typically medial to the focus activated by contralateral stimulation and was stereotaxically localized in the motor cortex; the other focus was typically posterior to the focus activated by contralateral stimulation and was stereotaxically localized in the somatosensory cortex. (3) Forepaw and hindpaw somatosensory stimuli activated large areas of the sensorimotor cortex, well beyond the forepaw and hindpaw somatosensory areas of classical somatotopic maps, and forepaw stimuli activated larger cortical areas with greater activation velocity than hindpaw stimuli. (4) Stimulation of the forepaw and hindpaw evoked different cortical activation dynamics: forepaw responses displayed a clear medial directionality, whereas hindpaw responses were much more uniform in all directions. In conclusion, this work offers a complete spatio-temporal map of the supragranular VSD cortical activation in response to stimulation of the paws, showing important somatotopic differences between contralateral and ipsilateral maps as well as differences in the spatio-temporal activation dynamics in response to forepaw and hindpaw stimuli.