共查询到20条相似文献，搜索用时 25 毫秒
1.
Fricke C Lee JS Geiger-Rudolph S Bonhoeffer F Chien CB 《Science (New York, N.Y.)》2001,292(5516):507-510
As growing retinotectal axons navigate from the eye to the tectum, they sense guidance molecules distributed along the optic pathway. Mutations in the zebrafish astray gene severely disrupt retinal axon guidance, causing anterior-posterior pathfinding defects, excessive midline crossing, and defasciculation of the retinal projection. Eye transplantation experiments show that astray function is required in the eye. We identify astray as zebrafish robo2, a member of the Roundabout family of axon guidance receptors. Retinal ganglion cells express robo2 as they extend axons. Thus, robo2 is required for multiple axon guidance decisions during establishment of the vertebrate visual projection. 相似文献
2.
The topographic map of cell position in the avian retina is inverted in its projection to the optic tectum. Dorsal retinal ganglion cell axons project to ventral tectum, and ventral retinal ganglion cells project to dorsal tectum. Topographic gradients of toponymic (TOP) cell surface molecules along the dorsoventral axes of retina and tectum also are inverted. TOP molecules are most abundant in dorsal retina and ventral tectum and least abundant in ventral retina and dorsal tectum during the period of initial retinal-tectal interaction. Thus, TOP molecules may be involved in orienting the retinotectal map. 相似文献
3.
α6/α3β4烟碱型乙酰胆碱受体（α6β4* nAChRs,*代表其他亚基）主要分布于大脑海马区、外周神经节和人源肾上腺嗜铬细胞等,与神经性疼痛和炎症反应、情绪等生理疾病密切相关。本研究拟对大鼠α6/α3β4 nAChR在非洲爪蟾（Xenopus laevis）卵母细胞膜上进行重组表达,并利用双电极电压钳电生理学技术检测该重组受体的功能。在不同浓度的激动剂乙酰胆碱的刺激下,比较了α6/α3和β4亚基的不同配比形成的受体通道开放而产生的电流大小,并用其拮抗剂α?芋螺毒素TxID验证了该受体的敏感性。结果表明,亚基不同配比的α6/α3β4 nAChR均可在非洲爪蟾卵母细胞膜上成功表达,并具有较好的配体门控敏感性。 相似文献
4.
Del Bene F Wyart C Robles E Tran A Looger L Scott EK Isacoff EY Baier H 《Science (New York, N.Y.)》2010,330(6004):669-673
The optic tectum of zebrafish is involved in behavioral responses that require the detection of small objects. The superficial layers of the tectal neuropil receive input from retinal axons, while its deeper layers convey the processed information to premotor areas. Imaging with a genetically encoded calcium indicator revealed that the deep layers, as well as the dendrites of single tectal neurons, are preferentially activated by small visual stimuli. This spatial filtering relies on GABAergic interneurons (using the neurotransmitter γ-aminobutyric acid) that are located in the superficial input layer and respond only to large visual stimuli. Photo-ablation of these cells with KillerRed, or silencing of their synaptic transmission, eliminates the size tuning of deeper layers and impairs the capture of prey. 相似文献
5.
Nicotinic antagonists enhance process outgrowth by rat retinal ganglion cells in culture 总被引：2，自引：0，他引：2
S A Lipton M P Frosch M D Phillips D L Tauck E Aizenman 《Science (New York, N.Y.)》1988,239(4845):1293-1296
Functional nicotinic cholinergic receptors are found on mammalian retinal ganglion cell neurons in culture. The neurotransmitter acetylcholine (ACh) can be detected in the medium of many of these retinal cultures, after release presumably from the choline acetyltransferase-positive amacrine cells. The postsynaptic effect of endogenous or applied ACh on the ganglion cells can be blocked with specific nicotinic antagonists. Here it is shown that within 24 hours of producing such a pharmacologic blockade, the retinal ganglion cells begin to sprout or regenerate neuronal processes. Thus, the growth-enhancing effect of nicotinic antagonists may be due to the removal of inhibition to growth by tonic levels of ACh present in the culture medium. Since there is a spontaneous leak of ACh in the intact retina, the effects of nicotinic cholinergic drugs on process outgrowth in culture may reflect a normal control mechanism for growth or regeneration of retinal ganglion cell processes that is exerted by ACh in vivo. 相似文献
6.
Acetylcholine receptors: number and distribution at neuromuscular junctions in rat diaphragm 总被引：38，自引：0，他引：38
The number of acetylcholine receptors per motor end plate in the rat diaphragm, measured by the binding of [(125)1]alpha-bungarotoxin, varies directly with rat size and is (4.0 +/- 0.2) x 10(7) for full-grown male rats. Autoradiographic analysis of single fibers labeled with this substance reveals that virtually all of these receptors are localized in the end plate. 相似文献
7.
The number of acetylcholine receptors was determined in the neuromuscular junctions of eight patients with typical myasthenia gravis and in five controls, by means of (125)1-labeled alpha-bungarotoxin binding. The junctional acetylcholine receptors were reduced in the myasthenic muscles as compared with the controls. This reduction in receptors may account for the defect in neuromuscular transmission in myasthenia gravis. 相似文献
8.
为了进一步探究第11位氨基酸的性质对LvIA靶点结合活性的影响，设计了LvIA的2个新型突变体[D11R]LvIA和[D11H]LvIA，即用2个碱性氨基酸?精氨酸（R）和组氨酸（H）分别替换原来的酸性氨基酸D。先人工合成了这2个新突变体的线性肽，然后采用2步氧化法进行折叠，以获得在第1位和第3位半胱氨酸（Cys 1～3）、第2位和第4位半胱氨酸（Cys 2～4）之间定点连接形成二硫键。经高效液相色谱分离纯化和质谱鉴定，合成了含有Cys(1～3, 2～4)二硫键连接方式的多肽，其分子质量正确，纯度在95%以上。利用双电极电压钳电生理学技术对这2种突变体与α3β2 nAChR的结合活性进行了检测。结果发现，当该位点的氨基酸性质由酸性转换为碱性后，对LvIA的活性影响巨大，直接导致对α3β2 nAChR的阻断活性丧失。[D11R]LvIA和[D11H]LvIA的活性与野生型LvIA相比分别降低了574.38%和408.62%。由此表明，第11位氨基酸的酸碱性对LvIA的活性至关重要。 相似文献
9.
Conduction velocity variations minimize conduction time differences among retinal ganglion cell axons 总被引：1，自引：0，他引：1
L R Stanford 《Science (New York, N.Y.)》1987,238(4825):358-360
The visual system is able to accurately represent the spatiotemporal relations among the elements of a changing visual scene as the image moves across the retinal surface. This precise spatiotemporal mapping occurs despite great variability in retinal position and conduction velocity even among retinal ganglion cells of the same physiological class-a variability that would seem to reduce the precision with which spatiotemporal information can be transmitted to central visual areas. There was a strong negative relation between the intraretinal and extraretinal conduction time for axons of individual ganglion cells of the X-cell class. The effect of this relation was to produce a nearly constant total transmission time between the soma of a retinal X cell and its central target site. Thus, the variation in the conduction velocities of retinal ganglion cell axons may ensure that, regardless of the constraints imposed by retinal topography, a precise spatiotemporal central representation of the retinal image is maintained. 相似文献
10.
A small amount of horseradish peroxidase, injected into the goldfish optic nerve and transported into the retina, filled an annulus of ganglion cells. Since the retina grew by annular addition of cells, this result shows that axons from cells of similar age clustered together in the nerve. 相似文献
11.
Serum globulin in myasthenia gravis: inhibition of alpha-bungarotoxin binding to acetylcholine receptors 总被引：35，自引：0，他引：35
Serum factors that inhibit the binding of (125)I-labeled alpha-bungarotoxin to the acetylcholine receptor extracted in detergent from denervated rat muscle were detected by a sensitive assay. The serum of at least 5 and possibly 11 out of 15 patients with myasthenia gravis showed inhibitory activity that was localized to the globulin fraction. No controls showed inhibitory activity. The demonstration of inhibitory globulins may help explain the involvement of the immune system in the pathophysiology of the neuromuscular junction in patients with myasthenia gravis. 相似文献
12.
Rats with geniculate laminae that run perpendicular to the lines of projection are described. Earlier reports of laminae parallel to the lines of projection were based on mammalian mutants that may be relatively common. In these mutants, the chiasmatic course of axons arising in a patch of retinal ganglion cells is wrongly specified. 相似文献
13.
Transport of protein by goldfish optic nerve fibers 总被引：4，自引：0，他引：4
B Grafstein 《Science (New York, N.Y.)》1967,157(785):196-198
After tritiated leucine was injected into the eye of goldfish, radio-active protein synthesized by the ganglion cell bodies moved down the optic axons at an average rate of 0.4 mm per day. Radioautograms of the optic tectum in which these axons end show that, as early as 24 hours after the injection, before the radioactivity in the tectal layer containing the optic axons had risen above background level, the layer containing the axon terminals was already heavily labeled. The radioactivity in the terminals reached a maximum about 48 hours after the injection and remained approximately constant for at least 23 days thereafter, whereas the radioactivity in the fiber layer increased significantly during the same interval, as the slowly moving protein component entered it. Thus there appears to be a special mechanism for rapid transport of protein from the cell body to the synaptic terminals, as well as a slower movement of protein down the axon. 相似文献
14.
Radioautography of the optic tectum of the goldfish, performed after injection of [(3)H]proline into the contralateral eye, effectively resolves several distinct layers of retinal synapses. Silver grains are found unilaterally over nerve tracts containing efferent fibers from the tectum, a result that suggests intercellular migration of labeled molecules. The low background and high specific grain density obtained with [(3)H]proline radioautography indicate the usefulness of this technique for the elucidation of neuroanatomical connections in the visual system. 相似文献
15.
Acuity falls sharply and predictably in man as fixation is shifted away from the test stimulus. If the same "eccentricity" function applies to the monkey, then it can be shown that striate cortex lesions produce a smaller acuity impairment than is predicted by electrophysiological maps of the projection of retina onto the cortex. It is seen in this study that retinal lesions of the fovea and adjacent parafovea produce a more severe drop in acuity than corresponding cortical lesions, and therefore the surprisingly slight effects of the latter cannot be explained in terms of a relatively higher parafoveal acuity in the monkey. The discrepancy between retinal and cortical effects is unlikely to be due to the development of "supersensitivity" at the edge of the cortical lesions. An explanation is proposed in terms of lateral spread of information at retinal and/or geniculate stages of the visual system. 相似文献
16.
J P Raynauld 《Science (New York, N.Y.)》1972,177(43):84-85
After light adaptation, all "on-center" ganglion cells in the dark became "red on-center," and all "off-center" cells turned into "red off-center" cells. On a chance basis, this similitude of effect between the rods and the red cones in opponent color cells was not expected. These findings indicate that in the goldfish there is some similarity between the connections of the rods and of the long-wavelength cones. 相似文献
17.
Functional expression of a new pharmacological subtype of brain nicotinic acetylcholine receptor 总被引：20，自引：0，他引：20
K Wada M Ballivet J Boulter J Connolly E Wada E S Deneris L W Swanson S Heinemann J Patrick 《Science (New York, N.Y.)》1988,240(4850):330-334
A new type of agonist-binding subunit of rat neuronal nicotinic acetylcholine receptors (nAChRs) was identified. Rat genomic DNA and complementary DNA encoding this subunit (alpha 2) were cloned and analyzed. Complementary DNA expression studies in Xenopus oocytes revealed that the injection of messenger RNAs (mRNAs) for alpha 2 and beta 2 (a neuronal nAChR subunit) led to the generation of a functional nAChR. In contrast to the other known neuronal nAChRs, the receptor produced by the injection of alpha 2 and beta 2 mRNAs was resistant to the alpha-neurotoxin Bgt3.1. In situ hybridization histochemistry showed that alpha 2 mRNA was expressed in a small number of regions, in contrast to the wide distribution of the other known agonist-binding subunits (alpha 3 and alpha 4) mRNAs. These results demonstrate that the alpha 2 subunit differs from other known agonist-binding alpha-subunits of nAChRs in its distribution in the brain and in its pharmacology. 相似文献
18.
Ouabain, when applied to the periotic spaces, that is, to the basal end of the saccular hair cells, suppressed microphonic potentials of the inner ear in goldfish. In contrast, streptomycin produced such an effect only when it was applied directly into the endolymph, that is, to the hair-bearing ends of the hair cells. 相似文献
19.
Cat X retinal ganglion cells that can resolve sine gratings of only 2.5 cycles per degree can nevertheless respond reliably to displacements of a grating of approximately 1 minute of arc. This is a form of hyperacuity comparable in magnitude to that seen in human vision. A theoretical analysis of this form of hyperacuity reveals it to be a result of the high gain and low noise of ganglion cells. The hyperacuity expected for the best retinal ganglion cells is substantially better than that observed in behavioral experiments. Thus the brain, rather than improving on the retinal signal-to-noise ratio by pooling signals from many ganglion cells, is unable to make use of all the hyperacuity information present in single ganglion cell responses. 相似文献
20.
The nicotinic acetylcholine receptors （nAchRs） are cholinergic receptors that form ligand-gated ion channels by ifve subunits in insect and vertebrate nervous systems. The insect nAChR is the molecular target of a class of insecticides, neonicotinoids. Here, we identiifed and cloned 11 candidate nAChR subunit genes in Acyrthosiphon pisum using genome-based bioinformatics combined modern molecular techniques. Most A. pisum nAChRs including α1, α2, α3, α4, α6, α8, and β1 show highly sequence identities with the counterparts of other insects examined. Expression proifles analysis showed that all subunit genes were expressed in adult head. At least two subunits have alternative splicing that obviously increase A. pisum nicotinic receptor diversity. This study will be invaluable for exploring the molecular mechanisms of neonicotinoid-like insecticides in sucking pests, and for ultimately establishing the screening platform of novel insecticides. 相似文献