Synapses onto different morphological types of retinal ganglion cells

The percentage of bipolar and amacrine synapses onto ganglion cell dendrites of the ground squirrel has been determined by electron microscopy of cells impregnated by the Golgi method. One group of ganglion cells has mainly amacrine input (approximately 97 percent); the other group has an approximately equal bipolar and amacrine input. Morphologically distinct types of ganglion cells usually have a consistent synaptic input, but exceptions may exist.     

Unusual retinal cells in the dolphin eye

By comparison to the cellular constituents of the retinas of certain other diving mammals, the elements of the dolphin retina include an unusually large number of specialized cells. Both cone and rod receptors may be identified. An unusual amacrine cell may be seen which produces a process that spans the cells between the inner plexiform and outer plexiform layers. Most unusual is a layer of giant ganglion cells which appears to serve most of the central retina. The giant ganglion cells support giant dendrites and optic nerve fibers which range up to 8 micrometers in diameter.     

Eye-specific retinogeniculate segregation independent of normal neuronal activity

The segregation of initially intermingled left and right eye inputs to the dorsal lateral geniculate nucleus (DLGN) during development is thought to be in response to precise spatial and temporal patterns of spontaneous ganglion cell activity. To test this hypothesis, we disrupted the correlated activity of neighboring ganglion cells in the developing ferret retina through immunotoxin depletion of starburst amacrine cells. Despite the absence of this type of correlated activity, left and right eye inputs segregated normally in the DLGN. By contrast, when all spontaneous activity was blocked, the projections from the two eyes remained intermingled. Thus, certain features of normal neural activity patterns are not required for the formation of eye-specific projections to the DLGN.     

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.     

GDF11 controls the timing of progenitor cell competence in developing retina

The orderly generation of cell types in the developing retina is thought to be regulated by changes in the competence of multipotent progenitors. Here, we show that a secreted factor, growth and differentiation factor 11 (GDF11), controls the numbers of retinal ganglion cells (RGCs), as well as amacrine and photoreceptor cells, that form during development. GDF11 does not affect proliferation of progenitors-a major mode of GDF11 action in other tissues-but instead controls duration of expression of Math5, a gene that confers competence for RGC genesis, in progenitor cells. Thus, GDF11 governs the temporal windows during which multipotent progenitors retain competence to produce distinct neural progeny.     

Nicotinic antagonists enhance process outgrowth by rat retinal ganglion cells in culture

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.     

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.     

Receptive field mechanism in the vertebrate retina

In the catfish retina there are two types of ganglion cells: in one type (type A cell) a spot of light at the center of its receptive field gives rise to a sustained discharge whereas an annulus gives rise to a transient response, and in the other type (type B cell) the response pattern is reversed for a spot and an annulus. Current injected into the horizontal cell induces spike discharges of the ganglion cell very similar to that elicited by a spot of light or by an annulus. In both types of receptive fields, depolarization of the horizontal cell gives rise to a response of the ganglion cell similar to that elicited by a spot of light, whereas hyperpolarization of the cell gives rise to a response of the ganglion cell similar to that elicited by an annulus. Current through a single injecting electrode could drive two types of cells simultaneously. Interaction between a spot of light and an annulus can also be simulated by replacing one light stimulus by current of the proper polarization injected into the horizontal cells. Results suggest that interactions among three neuronal structures, the receptor, the horizontal cell, and the bipolar cell, produce the basic receptive field organization in the channel catfish.     

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.     

Adrenergic innervation of the parasympathetic ciliary ganglion in the chick

The chick ciliary ganglion receives a nonvascular symathetic innervation in addition to the well-known cholinergic one; fluorescent, varicose adrenergic fibers form pericelluar baskets. Adrenergic fibes were identified electron microscopically in ganglia fixed with potassium permanganate. The fibers degenerate after injection of 6-hydroxydopamine. No true synaptic relationships involving adrenergic varicosities and ganglion cells or cholinergic terminals were demonstrable. The distribution of the adrenergic fibers suggests a kind of "distance à synapse" with the choroidal cells or with the preganglionic fibers (or both). The adrenergic innervation might provide a modulation of the cholinergic transmission.     

Central neuron initiation of periodic gill movements

In Aplysia periodic spontaneous gill movements are controlled by activity endogenous to the abdominal ganglion. These movements were still observed when only the ctenidio-genital nerve was left intact between the ganglion and the gill. One kind of spontaneous gill movement (one per 5 minutes at 15 degrees C) was correlated with the expression of activity of interneuron II; others were not. With reference to this kind of spontaneous gill movement, four types of central neurons in the ganglion send processes to the gill via the nerve. Two cell types (ii, iii) are inhibited and the other two (i, iv) are excited. Two types (i, ii) elicited gill movement-one type activating large gill areas elicited spontaneous gill movements, and the other activating specific gill regions did not participate in the spontaneous gill movements. The value of this preparation in studying the role of central neurons eliciting specific patterned movements and the temporal organization of their activity is shown.     

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.     

Amacrine-signaled loss of intrinsic axon growth ability by retinal ganglion cells

The central nervous system (CNS) loses the ability to regenerate early during development, but it is not known why. The retina has long served as a simple model system for study of CNS regeneration. Here we show that amacrine cells signal neonatal rat retinal ganglion cells (RGCs) to undergo a profound and apparently irreversible loss of intrinsic axon growth ability. Concurrently, retinal maturation triggers RGCs to greatly increase their dendritic growth ability. These results suggest that adult CNS neurons fail to regenerate not only because of CNS glial inhibition but also because of a loss of intrinsic axon growth ability.     

An excitatory amino acid antagonist blocks cone input to sign-conserving second-order retinal neurons

cis-2,3-Piperidinedicarboxylic acid (PDA), an excitatory amino acid antagonist, reversibly blocked cone input to OFF bipolars and horizontal cells, whereas ON bipolars were relatively unaffected. Kainic acid effects were also blocked, indicating a postsynaptic mechanism of action. The use of PDA helps to characterize one of two classes of excitatory amino acid synaptic receptors that mediate cone influence in the outer retina.     

克氏原螯虾X器官-窦腺复合体的组织学观察

应用组织切片技术观察了克氏原螯虾眼柄神经内分泌系统的结构,研究了XO-SG复合体的分布.结果表明,克氏原螯虾眼柄神经内分泌系统主要组成部分为X器官-窦腺复合体.X器官分布在视神经节上,由Ⅰ～Ⅵ型6种神经分泌细胞构成,均为单级神经元.Ⅰ～Ⅵ型分泌细胞类型及数量在不同生长期存在差异.窦腺位于视内髓与视端髓之间的背内侧,由窦腺壁和中央血窦腔组成;窦腺壁由神经分泌细胞的末梢、神经胶质细胞及其突起交织而成.     

Diminished pupillary light reflex at high irradiances in melanopsin-knockout mice

In the mammalian retina, a small subset of retinal ganglion cells (RGCs) are intrinsically photosensitive, express the opsin-like protein melanopsin, and project to brain nuclei involved in non-image-forming visual functions such as pupillary light reflex and circadian photoentrainment. We report that in mice with the melanopsin gene ablated, RGCs retrograde-labeled from the suprachiasmatic nuclei were no longer intrinsically photosensitive, although their number, morphology, and projections were unchanged. These animals showed a pupillary light reflex indistinguishable from that of the wild type at low irradiances, but at high irradiances the reflex was incomplete, a pattern that suggests that the melanopsin-associated system and the classical rod/cone system are complementary in function.     

Hexokinase isoenzymes in human erythrocytes

The electrophoretic mobility of hexokinase from human erythrocytes and other tissues was studied with a new method that depends on the fluorescence of reduced nicotinamide-adenine dinucleotide phosphate for detecting enzyme activity on starch gel. The hexokinase of cord-blood erythrocytes has slightly different electrophoretic properties from that of adult red cells. Type I enzyme is split into type I(A) and type I(F); the latter is more intense in cord blood; in hemolyzates of adult blood, the activity of the two bands is usually about equal. No type II enzyme was found in cord blood. The double type I band was present in red cells from adult rabbits.     

Morphological identification of serotonin-accumulating neurons in the living retina

Neurons that accumulate the transmitter serotonin have been identified in the living retina by being labeled with 5,7-dihydroxytryptamine (5,7-HT), an autofluorescent serotonin analog. Iontophoretic injection of Lucifer yellow into the labeled cells under microscopic control revealed that the serotonin-accumulating neurons in rabbit retina constitute two morphological types of amacrine cells, termed S1 and S2, whose distal dendrites are stratified at the inner margin of the inner plexiform layer. The dendritic overlap of the S1 type is extraordinarily large: each point on the retina is covered by the fields of 550 to 900 S1 amacrines, and 6 to 8 meters of their dendrites are packed into each square millimeter of retina. Such a pervasive neuropil may provide an effective substrate for diffuse transmitter release, as proposed for serotonergic fibers elsewhere in the central nervous system.     

Dopamine-accumulating retinal neurons revealed by in vitro fluorescence display a unique morphology

Dopamine is the principal catecholamine neurotransmitter in the vertebrate retina. The shape of retinal neurons that accumulate dopamine has been demonstrated in an in vitro preparation of cat retina. This was achieved by the discovery that the combined uptake of dopamine and the indoleaminergic transmitter analog 5,7-dihydroxytryptamine leads to an intense, catecholamine-like fluorescence in the cell bodies and processes of presumed dopaminergic amacrine cells in the living retina. This fluorescence served as an in vitro marker for these cells, and their detailed morphology was analyzed after intracellular injection of horseradish peroxidase under direct microscopic control. The horseradish peroxidase-filled cells show an unprecedented neuronal morphology: each cell gives rise to multiple, axon-like processes that arise from, and extend for millimeters beyond, the dendritic tree. The unique structure of this type of amacrine cell suggests a function for dopamine in long-range lateral interactions in the inner plexiform layer.     

山西省棉花黄萎病菌致病力分化研究

选山西有代表性的棉花黄萎病菌19个菌系及3个对照菌种,各配成一定浓度的孢子悬浮液,于棉苗1～2叶期伤根接菌,在温室中对各代表菌系进行致病力测定。结果表明:各菌系致病力强弱差异明显,可分为致病力强的I型、致病力弱的II型和致病力中等的III型;并发现山西棉花黄萎病有落叶型菌系存在。