Blockade of visual excitation and adaptation in Limulus photoreceptor by GDP-beta-S

Light causes both depolarization and adaptation to light in Limulus ventral photoreceptors. Both visual excitation and adaptation were blocked by guanosine 5'-O-(2-thiodiphosphate) (GDP-beta-S), a metabolically stable analog of guanosine 5'-diphosphate (GDP). However, GDP-beta-S did not block the excitation caused by injection of inositol 1,4,5-trisphosphate into the cell. These results suggest a molecular cascade of visual excitation and adaptation: Light isomerizes the visual pigment rhodopsin, which in turn activates a guanyl nucleotide-binding protein. The binding protein then stimulates production of inositol 1,4,5-trisphosphate, which causes release of calcium from the endoplasmic reticulum.     

Photoelectric potential from photoreceptor cells in ventral eye of Limulus

Intense colored light from a gas laser evokes a photoelectric potential in the photoreceptor cells of the ventral eye of Limulus. This potential has two components, both of which have the action spectrum of a rhodopsin with an absorbancy maximum at 530 nm. The evidence is consistent with the hypothesis that the photoelectric potential arises directly from the orderly array of rhodopsin molecules which are an integral part of the photoreceptor cell membrane.     

Masking in visual recognition: effects of two-dimensional filtered noise

It is difficult to recognize portraits that have been coarsely sampled and quantized. Blurring such images improves recognition. A simple, straightforward explanation is that high-frequency noise introduced by the sampling and quantizing must be removed by low-pass filtering to improve the signal-to-noise ratio and hence signal detectability or recognition. Experiments reported here, suggested on the basis of a different model, show instead that noise bands that are spectrally adjacent to the picture's spectrum are considerably more effective in suppressing recognition.     

鲎C因子的研究进展

鲎C因子是鲎血细胞中一种对内毒素敏感的丝氨酸蛋白酶原,主要有6种结构域,能特异结合内毒素而被激活.对鲎C因子的结构与功能、基因工程研究及其应用前景进行了综述.     

The contribution of noise to contrast invariance of orientation tuning in cat visual cortex

Feedforward models of visual cortex appear to be inconsistent with a well-known property of cortical cells: contrast invariance of orientation tuning. The models' fixed threshold broadens orientation tuning as contrast increases, whereas in real cells tuning width is invariant with contrast. We have compared the orientation tuning of spike and membrane potential responses in single cells. Both are contrast invariant, yet a threshold-linear relation applied to the membrane potential accurately predicts the orientation tuning of spike responses. The key to this apparent paradox lies in the noisiness of the membrane potential. Responses that are subthreshold on average are still capable of generating spikes on individual trials. Unlike the iceberg effect, contrast invariance remains intact even as threshold narrows orientation selectivity. Noise may, by extension, smooth the average relation between membrane potential and spike rate throughout the brain.     

Conductance changes associated with receptor potentials in Limulus photoreceptors

The receptor potential in Limulus photoreceptors appears to be a consequence not of permeability changes in the cell membrane but of alterations in a light-sensitive constant-current generator.     

A role for the sodium pump in photoreception in Limulus

The membranes of photoreceptor cells in Limulus have an electrogenic sodium pump which contributes directly to membrane potential and whose activity is changed by light. These light-induced changes in pump activity underlie the receptor potential.     

鲎血水解液美拉德反应产物的挥发性成分研究

以制备鲎试剂产生的废料血浆为原料,经盐酸水解后,水解液进行美拉德反应,通过固相微萃取-气相色谱-质谱法(SPME-GC-MS)测定反应产物中的挥发性成分,分析了其呈香机理。结果表明,鲎血水解液在p H为8.0,100℃加热2 h,其美拉德反应的褐变程度最强,确定了39种挥发性成分,主要包括烃类5.13%、酮类1.47%、酸类2.64%、醛类14.08%、酯类1.24%、酚类0.84%、醇类4.33%及含氮化合物0.26%。该结果可为开发苯甲醛、食品香精及卷烟改良剂等方面提供参考。     

Intracellular absorption difference spectrum of Limulus extra-ocular photolabile pigment

Microspectrophotometric measurements on single cell bodies located on the surface of the"lateral olfactory nerve" of Limulus polyphemus show they contain a photolabile pigment with a absorption-difference spectrum similar in shape to that of most other visual pigments and with a maximum absorption at 529 +/- 5 nanometers.     

Limulus lateral eye: properties of receptor units in the unexcised eye

Single receptor units in the compound eye of the horseshoe crab were illuminated, and their impulse discharges were recorded without removing the eye from the animal. The receptors were spontaneously active in darkness and responded without saturation over a light intensity range of 10(10) to 1. When the eye was excised, the receptors did not discharge in darkness and had an intensity range of 10(5) to 1, as is usually found. Experiments show that these and other differences result from cutting off the blood supply to the eye when it is excised. In addition, the range and shape of the intensity characteristic suggest that more than one receptor mechanism encodes light intensity in this eye.     

A hyperpolarizing component of the receptor potential in the median ocellus of Limulus

There are two classes of photoreceptor cells in the median ocellus of Limulus. One class of cells respond to long wavelength (visible) stimuli with a depolarizing receptor potential and to near ultraviolet light with a biphasic, initially hyperpolarizing, receptor potential. The other class of receptors respond with a depolarization to near ultraviolet and with a biphasic response to visible light. In the latter type of cell, visible light can counteract the depolarization elicited by near ultraviolet light. The evidence suggests that there are two photopigments in each cell and that both are involved in the generation of receptor potential.     

Self-maintained visual stimulation in monkeys after long-term visual deprivation

Newborn monkeys reared in darkness for 16 months, except for daily 1-hour periods of exposure to unpatterned light, were allowed to press a lever to obtain unpatterned light. The animals showed apparently insatiable responding, at rates that were extremely high as compared with rates for normally reared control animals.     

Landslide noise

Acoustical monitoring of real landslides has revealed the existence of subaudible noise activity prior to failure and has enabled prediction of the depth of the seat of sliding when conducted in boreholes beneath the surface. Recordings of noise generated in small slopes of moist sand, tilted to failure in laboratory tests, have been analyzed to determine the foci of discrete subaudible noise events. The noises emitted shortly before failure were plotted close to the true sliding surface observed after failure. The foci of earlier events lay either within the central portion of the sliding mass or in a region behind the failure surface. The head and toe zones were devoid of strong seismic activity.     

北京公园绿地边缘植物景观降噪能力与视觉效果的综合研究

对城市公园绿地外道路噪声环境进行监测与分析的结果表明:公园边界噪音来源于车辆发动机噪音、胎噪、运动风声的综合噪声。这些噪音对公园游憩造成了或多或少的影响。如果公园绿地边缘部分的植物景观能够迅速降低噪音,又能展现美感,将对公园利用率的提高大有裨益。植物景观的视觉效果与生态效益都融合在园林植物中,所以一次设计将在多个层面展现植物景观的功能。以北京市公园绿地(被城市干道包围的绿地)边界的多个不同样方为对象,调查与研究这一宽度范围内的植物类型、种植密度和配置方式,从而判断使噪声衰减最有效率的植物配置形式。这些植物群落不仅能有效地减弱交通噪声,构造更为安静的游园环境,而且更能美化城市环境,体现并形成当地的植物特色。按照降噪效率对这些样方进行排序并运用SBE法对所测公园边界的植物群落进行美景度相应指标的评价,分析边界植物群落色彩美景度高低的原因,得到所测群落中景观效果最好的植物配置形式。综合以上两种最佳形式的植物配置,进行平衡与推断, 形成诸如同样的宽度条件下,多排小乔或低层灌木既可以起到较好的降噪作用,又可以丰富路缘的观赏效果;乔灌草皆有的种植模式中乔木排数尽可能多,林间内部保持通透,会形成舒适的空间效果等判断, 可以对北京市以及类似的大型城市绿地边缘塑造植物景观提供科学的论据。      

The response of living cells to very weak electric fields: the thermal noise limit

A physical model in which cells are considered as possible detectors of very weak periodic electric fields yields a general relation between cell size and both thermally induced fluctuations in membrane potential and the maximum change in membrane potential caused by an applied field. The simplest version of the model provides a broad-band estimate of the smallest applied electric field to which membrane macromolecules can directly respond (about 10(-3) volt per centimeter). Much smaller fields (10(-6) volt per centimeter) can be detected if there is a response in only a narrow band of frequencies or if signal averaging occurs through field-induced variation in the catalytic activity of membrane-associated enzymes. Both extensions of the simplest version remove the apparent violation of the thermal noise limit found in some experiments.     

Limulus rhodopsin: rapid return of transient intermediates to the thermally stable state

Spectral transitions of rhodopsin in single cells of the Limulus ventral eye were observed both with flash photometry and by measuring the early receptor potential. Even with repetitive stimulus flashes the rhodopsin did not bleach; after each flash the spectral intermediates decayed rapidly to the initial thermally stable state. The pigment returns to the stable state in a time comparable with the duration of the late receptor potential.