Receptive fields in the cat retina: a new type

A new type of receptive field of cat retinal ganglion cells is described and termed the "suppressed-by-contrast" type. The firing rate of these cells is suppressed by a variety of visual stimuli. However, it has not been possible to find a stimulus that increases the firing rate above the maintained level.     

Receptive field organization of the S-potential

The receptive fields of S-potentials have been studied in carp retinas. The relationship between the stimulus intensity and area of stimulation was examined for each component of three different types of S-potential. It appears that for each component there is full summation over a large portion of the retina, a type of organization different from that found in the ganglion cell.     

Receptive field organization of units in the first optic ganglion of diptera

Centripetal spike potentials were recorded from two classes of units (transient and sustained) in the intermediate chiasma of flies. On-off units were characterized by a transient discharge after the onset and cessation of a light spot presented within its elliptical receptive field. Receptive fields of sustaining units were composed of three roughly circular regions arranged adjacently along a line; stimulation of the center region elicited a sustainied discharge, whereas stimulation of either adjacent region elicited an off discharge. Adjacent regions antagonized the central region, for stimulation of either inhibited the discharge resulting from stimulation of the central region.     

Substance P activity in the bullfrog retina: localization and identification in several vertebrate species

Immunoreactive substance P is present in the bullfrog retina, possibly in two types of stratified amacrine cells, with their somas in the inner nuclear layer and their neuronal processes entering the inner plexiform layer and ramifying in sublayers 3 or 4 (or both). Occasionally, polygonal somas positive for substance P were found in the ganglion cell layer. Approximately 75 percent of the cell bodies positive for substance P and 65 percent of the radioimmunoassayable substance P were found in the superior half of the frog retina. On the basis of high-performance liquid chromatography, the immunoreactive substance P in the neural retina of the rat, monkey, or chick is similar to synthetic substance P, whereas this is not true of the immunoreactive substance P in the bullfrog or carp retina.     

Lateral interactions at inner plexiform layer of vertebrate retina: antagonistic responses to change

Lateral interactions at the inner plexiform layer of the retina of the mudpuppy were studied intracellularly after they were isolated from interactions at the outer plexiform layer with a special stimulus. The isolation was confirmed by recording no surround effect at bipolar cells under conditions that elicited a strong surround effect at ganglion cells. It appears that amacrine cell, which respond to spatiotemporal change at one retinal region, inhibit the response to change in on-off ganglion cells at adjacent sites.     

形成灰色烤烟的原因及机理

通过对土壤、烟株、烟叶生理生化指标分析及田间生态环境调查和盆栽试验,系统研究了形成灰色烤烟的原因及影响品质的机理.结果表明,烤烟灰色烟叶发生与植烟土壤pH偏低、根层土壤含水量过高、土壤通透性差有密切关系,而影响灰色烟叶发生和严重程度的直接原因是土壤和烟叶内Fe,Mn等离子含量过高所致.在土壤pH值偏低,土壤含水量过高,根层土壤通透性差的条件下,Fe,Mn由不易被吸收的高价态转化成容易被植物吸收的低价态,造成烟株体内吸收积累Fe,Mn过多,营养平衡失调,引起烟草出现生理性中毒.     

Major steps in vertebrate evolution

We have come to the end of our story-a long one, covering some half a billion years, it appears. A modern man or other higher vertebrate has traveled far from the simply built insensate type of creature seen in his ultimate metazoan ancestor among the pterobranchs. The course of this evolutionary progression is far from direct and simple, as some might believe to be the case; it is a trail with many twists and turns. Nor is there the slightest reason to attempt a teleological interpretation; there is no trace of design and direction toward an obvious goal. Quite in contrast, it seems clear in many stages of the series that the changes which have taken place are immediately beneficial ones, strongly subject to selection. Obvious, too, is the fact that special environmental factors, biological and physical, have added unexpected quirks to the story. The development of a motile "tadpole" larva at an early chordate stage led to a sharp shift in an evolutionary sequence which otherwise might have simply ended in a sedate filtering form of tunicate type. The development of plant life on the continents opened up to motile chordates a new environment into which few invertebrates could enter and in which the chordates flourished to progress to the vertebrate level. The need for armor as defense against eurypterid enemies appears to have initiated the development of bony skeletal structures, without which the higher vertebrates could never have developed. The widespread late Paleozoic condition of seasonal drought favored progressive developments which, with the attainment of a reptilian stage, had the happy accidental result of the vertebrate conquest of the land, a conquest aided by the emergence of the insects as a basic food supply. The long period of dinosaur dominance seems to have been responsible for the sharpened wits which made the mammalian descendants of the therapsids competent for terrestrial dominance when the reign of the ruling reptiles ended. The arboreal life of primates was finally abandoned by man, but tree-dwelling had endowed his ancestors with advances in brain, eyes, and hands that were highly advantageous when this relatively feeble creature descended to the ground. It has been a long and tortuous journey; but every stage of it shows its effects in the structures and functions of such an end product as ourselves (Fig. 4).     

Receptive fields of directionally selective units in the optic nerve of the ground squirrel

These units responded vigorously to stimuli moving entirely across their receptive field centers in one direction (preferred) and not at all when the direction of motion was reversed (null). The directional selectivity was the result of an inhibitory mechanism which prevented responses to null movements. Surrounding each field center was a concentric antagonistic region produced by a second inhibitory mechanism.     

Centrifugal effects in the avian retina

Electrical stimulation of the centrifugal fibers to the avian retina can disturb the balance between the excitatory and inhibitory system within the receptive fields of individual retinal ganglion cells. Although the mechanisms may vary from one unit to another, the effect is always to make them fire more readily and to a wider range of visual inputs.     

Hemichannel-mediated inhibition in the outer retina

An essential feature of the first synapse in the retina is a negative feedback pathway from horizontal cells to cones. Here we show that at this synapse, connexin26 forms hemichannels on horizontal cell dendrites near the glutamate release site of the cones. Blocking these hemichannels hyperpolarizes horizontal cells, modulates the Ca2+ channels of the cones, and abolishes all feedback-mediated responses. We propose a feedback mechanism in which the activity of the Ca2+ channels and the subsequent glutamate release of the cones are modulated by a current through these hemichannels. Because the current through the hemichannels depends on the polarization of the horizontal cells, their activity modulates the output of the cones.     

Receptive fields of opponent color units in the optic nerve of the ground squirrel

When mapped with white light, each receptive field consisted either of an excitatory ("on") center and a concentric inhibitory ("off") surround, or of the reverse arrangement. Monochromatic stimuli revealed that each receptive field was composed of two mutually antagonistic components (one excitatory, one inhibitory) which had different spectral sensitivities and different spatial distributions. For some units the two chromatic components had identical spatial distributions.     

Natural free-running period in vertebrate animal populations

Regression analysis (analysis of covariance) is contrasted with the conventional "mean period length" for estimating the length of period of the spontaneous activity frequency (free-running period) in population samples of Gila monsters (Heloderma suspectum) and kangaroo rats (Dipodomys merriami) in the Sonoran Desert. The mean period length in each population does not differ significantly from 24:00 hours (P > .05) and it does not differ significantly (P > .05) between the species studied; the probability that the free-running period a(in constant dark) in natural populations of Gila monsters and kangaroo rats is different from 24:00.0 is less than 1 in 1000 (P < .001). The so-called "mean period length" is of little or no use for precise determination of the period and phase relationships in circadian rhythms; moreover, it is entirely without value for statistical testing of differences either within or between populations.     

Visual pigment renewal in the mature frog retina

It has been demonstrated by autoradiography that radioactive amino acids serve as precursors for proteins which are subsequently incorporated into retinal rod outer segment discs in mature animals. By the isolation and purification of visual pigment from retinas of adult frogs after injection of tritiated leucine and phenylalanine, it has been shown that at least part of this labeled protein consists of visual pigment (rhodopsin).     

施磷水田田表排水磷素流失特征及其机制研究

通过人工排灌手段模拟雨季条件下水田田表排水,研究了水田面施无机磷肥及有机无机磷肥配施48 h后、以间隔48 h连续进行4次人工排灌的磷素流失特征及其机制.结果表明:首次排水的磷素流失形态以可溶性磷为主,而其后多次排水的磷素流失形态主要为固相磷;面施磷肥时配施有机肥能显著提高后3次排水的田表磷素流失量与流失负荷,但对4次排水累计的磷素流失总量并没有影响,而以全磷表征的磷肥表观流失率为9%～16%.     

Synaptic connections of the centrifugal fibers in the pigeon retina

The centrifugal fibers in the pigeon retina end in the inner nuclear layer and form two kinds of terminals, convergent and divergent. In the inner nuclear layer the fibers synapse with amnacrine and displaced ganglion cells. Because of their great number and their even distribution these fibers appear to constitute a system for the localized centrifugal control of the retinal functions.     

高压静电场作用机理的物理解释及其在农业中的应用

根据近年来高压静电场的发展,探讨了从大气电场、雷云电场以及到高压静电场作用机理的物理微观解释,研究高压静电技术在农业各领域中的应用,认识高压静电场促进农作物生长的规律,努力扩大高压静电场在农业领域中的各种应用范围,并以此看作是寻求向高科技技术进军的战略新起点,推动一次真正意义的农业技术革命。     

小麦田日本看麦娘对唑啉草酯的抗药性机制研究

为明确小麦田日本看麦娘对唑啉草酯的抗药性情况及潜在的抗药性机制,应用整株生物测定法测定了采自安徽省、江苏省多个日本看麦娘发生严重地区共19个日本看麦娘种群对唑啉草酯的抗药性水平,并选取6个高抗种群进行ACCase基因测序和GSTs活性测定,比较抗药性、敏感种群间的基因序列和GSTs活性差异,同时测定了AH-29对其他8种除草剂的敏感性。结果显示,9个日本看麦娘种群对唑啉草酯产生了高水平抗性,占被测总数的47.37%,抗性指数在12.70 ~ 38.77之间;种群AH-28、AH-29和JS-15的ACCase基因CT区域第1781位异亮氨酸（ATA）突变为亮氨酸（TTA）,种群AH-36和JS-16第2027位色氨酸（TGG）突变为半胱氨酸（TGT）,种群AH-34未发现突变;6个高抗种群体内GSTs活性经唑啉草酯处理后均明显高于同处理敏感种群AH-7;种群AH-29均对ACCase抑制剂炔草酯、烯草酮以及ALS抑制剂的甲基二磺隆和氟唑磺隆产生了高水平抗性,抗性指数分别为45.32、29.54、37.53和23.04;对三甲苯草酮产生了中水平抗性,对双草醚和啶磺草胺表现低抗,但对PSII抑制剂异丙隆较为敏感。研究表明,ACCase基因突变与GSTs活性增强是导致日本看麦娘种群对唑啉草酯产生抗药性的重要原因之一。