Dendritic computation of direction selectivity by retinal ganglion cells

Direction-selective ganglion cells (DSGCs) in the retina respond strongly when stimulated by image motion in a preferred direction but are only weakly excited by image motion in the opposite null direction. Such coding represents an early manifestation of complex information processing in the visual system, but the cellular locus and the synaptic mechanisms have yet to be elucidated. We recorded the synaptic activity of DSGCs using strategies to observe the asymmetric inhibitory inputs that underlie the generation of direction selectivity. The critical nonlinear interactions between the excitatory and inhibitory inputs took place postsynaptically within the dendrites of the DSGCs.     

Synchronous bursts of action potentials in ganglion cells of the developing mammalian retina

The development of orderly connections in the mammalian visual system depends on action potentials in the optic nerve fibers, even before the retina receives visual input. In particular, it has been suggested that correlated firing of retinal ganglion cells in the same eye directs the segregation of their synaptic terminals into eye-specific layers within the lateral geniculate nucleus. Such correlations in electrical activity were found by simultaneous recording of the extracellular action potentials of up to 100 ganglion cells in the isolated retina of the newborn ferret and the fetal cat. These neurons fired spikes in nearly synchronous bursts lasting a few seconds and separated by 1 to 2 minutes of silence. Individual bursts consisted of a wave of excitation, several hundred micrometers wide, sweeping across the retina at about 100 micrometers per second. These concerted firing patterns have the appropriate spatial and temporal properties to guide the refinement of connections between the retina and the lateral geniculate nucleus.     

Goldfish retina: sign of the rod input in opponent color ganglion cells

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.     

北京鸭视网膜移动性无长突细胞的分布

利用视神经溃变试验和Nissl染色法研究了北京鸭视网膜移动性无长突细胞 (dACs)的形态、大小与密度分布。北京鸭dACs是位于视网膜节细胞层的小神经元 ,核深染 ,胞质很少 ,细胞体呈圆形或卵圆形 ,细胞大小均一 ,平均面积为 19～ 2 5 μm2 。在视网膜中央有一个dACs高密度区即中央高密度区 (CA ,386 0个·mm-2 ) ,dACs的密度由视网膜中央部向视网膜周边部逐渐降低 (TP ,约为 1780个·mm-2 ;NP ,约为 176 0个·mm-2 )。试验结果表明北京鸭视网膜中央部和周边部的dACs大小差异不明显 ,但dACs在节细胞层密度分布不均 ,呈现由视网膜中央部至周边部密度梯度递减的变化     

Transient morphological features of identified ganglion cells in living fetal and neonatal retina

The function and morphology of retinal ganglion cells in the adult mammalian visual system has been well studied, but little is known about how the adult state is achieved. To address this question, the morphological changes that retinal ganglion cells undergo during development were studied. Ganglion cells were first identified by retrograde labeling with rhodamine latex microspheres deposited in retinorecipient targets in fetal and early postnatal cats. The structure of ganglion cells was then revealed by intracellular injection of Lucifer yellow in living retinas removed and maintained in vitro. As early as 2 weeks before birth, a morphologically diverse assortment of ganglion cells is present, some of which resemble the alpha, beta, and gamma classes found in the adult. However, in contrast to the adult, developing ganglion cells exhibit several transient features, including excessive axonal and dendritic branching and exuberant somatic and dendritic spines. These morphological features indicate that there is a transient network of connectivity that could play an important role in the final determination of retinal ganglion cell form and function.     

Acetylcholinesterase: method for demonstration in amacrine cells of rabbit retina

The activity of acetylcholinesterase in the inner plexiform layer of the rabbit retina was not affected detectably by prior section of the optic nerve. After the animals were treated with diisopropyl phosphorofluoridate, acetylcholinesterase reappeared in the somata of the amacrine cells and in certain cells of the ganglion cell layer before it reappeared in the inner plexiform fibers. This confirms the normal presence of acetylcholinesterase at the former site. The possible role of acetylcholine in intraretinal transmission is considered.     

Neuronal population coding of movement direction

Although individual neurons in the arm area of the primate motor cortex are only broadly tuned to a particular direction in three-dimensional space, the animal can very precisely control the movement of its arm. The direction of movement was found to be uniquely predicted by the action of a population of motor cortical neurons. When individual cells were represented as vectors that make weighted contributions along the axis of their preferred direction (according to changes in their activity during the movement under consideration) the resulting vector sum of all cell vectors (population vector) was in a direction congruent with the direction of movement. This population vector can be monitored during various tasks, and similar measures in other neuronal populations could be of heuristic value where there is a neural representation of variables with vectorial attributes.     

Frog retina: detection of movement

The response of class 2 ganglion cells in the frog retina is dependent on the angular velocity of a black visual stimulus whose size (1.20 degrees ) and contrast against a background are held constant. The relation between neuronal discharge rate and the angular velocity of the stimulus may be expressed as a power function.     

Differential sensitivity of peripheral retina to intermittent white light

The ability of the eye to detect differences in the interruption rate of white light was investigated for various rates and for several locations onthe temporal periphery of the right eye. The complex relationship previously reported was again found, but only for stimulation of the fovea. The results from the peripheral regions indicate that differential sensitivity is adecreasing function of the rate of intermittence.     

Direction-selective units in rabbit retina: distribution of preferred directions

The preferred directions of 102 direction-selective ganglion cells in the rabbit retina have been determined. Cells of the "on-off" type form four nonoverlapping groups; cells of the "on" type fall into three groups. The on-off groups appear to correspond to the directions of apparent object displacement produced by contractions of the four rectus muscles. Each group of cells could, without further processing, provide the error signal for a visual servo-systerm minimizing retinal image motion.     

草兔对幼树的选择危害及其防治技术研究

调查了黄土高原退耕还林区草兔(Lepuscapensis)对常见造林树种的危害程度与危害症状,并采取不同防治措施进行了防治效果试验。结果表明,草兔主要危害郁闭前的幼树,在调查的26种树木中,7种危害严重,10种危害中等,9种危害较轻。防治试验结果表明,春季用牛油或废柴油涂干处理的苗木被害率较对照降低50.2%或48.7%;造林时对裸根苗用多效抗旱驱鼠剂150倍水溶液兑成泥浆蘸根,苗木被害率降低32.3%;苗木生长期用多效抗旱驱鼠剂400～500倍水溶液叶面喷施、篱障阻隔、阻隔与药泥蘸根或阻隔与叶面喷施相结合,均对草兔危害有一定的防治作用,各处理苗木被害率分别较对照降低了25.5%,63.0%,80.2%和74.5%。其中以篱障阻隔与药剂泥浆蘸根造林技术相结合对草兔的预防效果最好。     

Hyperacuity in cat retinal ganglion cells

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.     

Responses of retinal ganglion cells to exponentially increasing light stimuli

Action potentials of ganglion cells were recorded extracellularly from opened cat eyes. It was found that inhibition, as judged by discharge frequency, may depend upon rate of change of light intensity. Apparently the balance between excitatory and inhibitory inputs at the ganglion cell level depends upon rate of change of illumination. Visual purple bleaching or sensory adaptation taking place during the stimulation does not explain the results.     

Selective visual experience fails to modify receptive field properties of rabbit striate cortex neurons

During development, rabbits were exposed only to vertical or horizontal lines to determine if the receptive field characteristics of visual cortex cells would be altered as they are in the cat. Motion and directional selectivity were preserved, and orientation specificity remained unaffected by the restricted experience, which suggests that the rabbit may lack the neural plasticity seen in some other mammals.     

Rhodopsin photoproducts: effects on electroretinogram sensitivity in isolated perfused rat retina

Isolated perfused retinas of albino rats were exposed to brief saturating flashes of white light which bleached about 50 percent of the rhodopsin present. Transient photoproducts of the reaction could be detected for about 30 minutes. The b-wave threshold increased by some 3 logarithmic units immediately after the flash and remained stable at this level thereafter. This suggests that the longer-lived intermediate products of rhodopsin photolysis do not influence scotopic visual sensitivity.     

碱性成纤维细胞生长因子对视网膜组织中一氧化氮及其合成酶的影响

目的：观察碱性成纤维细胞生长因子(bFGF)对成年家兔体外培养的视网膜组织的一氧化氮(NO)及其合成酶(NOS)的影响,旨在为视网膜移植提供抗氧化的保护方法。方法：健康成年家兔20只(40眼),分成4组．Ⅰ(新鲜视网膜组)、Ⅱ(常规培养液组)、Ⅲ(高浓度bFGF液组)、Ⅳ(低浓度bFGF液组)．将Ⅱ～Ⅳ组视网膜组织块放入相应培养基中培养1周。4组视网膜取材后进行NO、NOS生化指标的测定。结果：Ⅰ～Ⅳ组视网膜组织NO、NOS含量差异有显著性．与Ⅰ组相比．Ⅱ、Ⅳ组NO、NOS值显著增高;与Ⅱ组相比．Ⅲ、Ⅳ组NO、NOS值显著降低;Ⅲ组与Ⅰ组NO值统计学差异无显著性意义。Ⅲ组与IV组比较．NOS值降低明显。结论：bFGF有清除自由基、增强抗氧化能力的作用．并且高浓度bFGF较低浓度bFGF对体外培养的视网膜组织抗氧化作用显著。     

Synaptic transmission between photoreceptors and horizontal cells in the turtle retina

Low calcium, high magnesium, and cobalt hyperpolarize the horizontal cell membrane and suppress the response to light, but only partially affect the response of receptor cells. These observations are consistent with the interpretation that a depolarizing transmitter is released by photoreceptors in darkness. The hyperpolarizing response to light of the horizontal cells would then result from a reduction in the amount of transmitter released.     

Sex chromatin of cone cells of human retina

Each retinal cone cell of the female contains a sex-chromatin body not present in coinparable material from the male. Therefore the lack of detectable "patch" formation in female heterozygotes for red color-blindness (as expected from the X-inactivation hypothesis) cannot be attributed to failure of Barr-body formation.     

Grueneberg ganglion cells mediate alarm pheromone detection in mice

Alarm pheromones (APs) are widely used throughout the plant and animal kingdoms. Species such as fish, insects, and mammals signal danger to conspecifics by releasing volatile alarm molecules. Thus far, neither the chemicals, their bodily source, nor the sensory system involved in their detection have been isolated or identified in mammals. We found that APs are recognized by the Grueneberg ganglion (GG), a recently discovered olfactory subsystem. We showed with electron microscopy that GG neurons bear primary cilia, with cell bodies ensheathed by glial cells. APs evoked calcium responses in GG neurons in vitro and induced freezing behavior in vivo, which completely disappeared when the GG degenerated after axotomy. We conclude that mice detect APs through the activation of olfactory GG neurons.