Simulated bipolar cells in fovea of human retina

This static bipolar cell (BC) model of the human fovea is based on a number of reasonable assumptions. The human fovea is directly responsible for visual acuity and color vision. The fovea can be considered as having two parts; a central fovea with only red- and green-sensitive cones and a parafovea with blue-sensitive cones added to the other two. A cone mosaic can be precisely organized spatially into unit hexagons that specify inputs to horizontal cells (HC) and BCs. The retina up to and including BCs is piece-wise linear, i.e. at a given steady-state adapting light intensity BC outputs are linear functions of the physical image. BC centers receive inputs directly from weighted cones, while antagonistic surrounds receive inverted inputs from HCs. Appropriate optical and chromatic filtering due to the eye that are taken from human data are incorporated into the model. Chromatic aberrations are simulated by three separate point spread functions that also are taken from human data. Automatic gain control of cones is a function of intensity and wavelength of the steady adapting light.The major part of this work was done while the author was a Senior Research Associate of the National Research Council, USA     

Excitatory and inhibitory receptive fields of tectal cells are differentially modified by magnocellular and parvocellular divisions of the pigeon nucleus isthmi

It has been known that magnocellular and parvocellular divisions of the pigeon nucleus isthmi exert excitatory and inhibitory actions on tectal cells, respectively. The present study shows that injection of N-methyl-D-aspartate into the parvocellular division results in an increase in responsive strength and extent of the inhibitory receptive fields, which expand into the excitatory receptive fields of tectal cells. This injection concurrently leads to a decrease in responsiveness and extent of the excitatory fields. On the other hand, injection of acetylcholine into the magnocellular division enhances visual responsiveness, although the excitatory field is not obviously changed in extent. Meanwhile, strength and extent of the inhibitory fields are decreased by acetylcholine. The excitatory and inhibitory fields are reduced in both strength and extent by magnocellular and parvocellular injection of lidocaine, respectively. It suggests that isthmic inputs from both parvocellular and magnocellular divisions converge onto the same tectal cells, and the magnocellular and parvocellular subnuclei can modulate excitatory and inhibitory receptive fields of tectal cells, respectively, with some interactions between both fields. Accepted: 1 March 2000     

The parvocellular LGN provides a robust disynaptic input to the visual motion area MT

Dorsal visual cortical areas are thought to be dominated by input from the magnocellular (M) visual pathway, with little or no parvocellular (P) contribution. These relationships are supported by a close correlation between the functional properties of these areas and the M pathway and by a lack of anatomical evidence for P input. Here we use rabies virus as a retrograde transynaptic tracer to show that the dorsal area MT receives strong input, via a single relay, from both M and P cells of the lateral geniculate nucleus. This surprising P input, likely relayed via layer 6 Meynert cells in primary visual cortex, can provide MT with sensitivity to a more complete range of spatial, temporal, and chromatic cues than the M pathway alone. These observations provide definitive evidence for P pathway input to MT and show that convergence of parallel visual pathways occurs in the dorsal stream.     

Catecholamine distribution and relationship to magnocellular neurons in the paraventricular nucleus of the rat

Summary The distribution of catecholamine synthesizing enzymes within the paraventricular nucleus of the rat hypothalamus is elucidated immunocytochemically by use of antibodies to tyrosine hydroxylase, dopamine -hydroxylase, and phenylethanolamine-N-methyltransferase. Tyrosine hydroxylase-immunostained cell bodies are localized in the periventricular stratum and adjacent parvocellular regions, but rarely in magnocellular subnuclei of the paraventricular nucleus. Tyrosine hydroxylase-immunostained fibers are present in greatest density in the periventricular zone, and moderate density in the parvocellular and magnocellular subnuclei. Dopamine -hydroxylase-immunostained fibers are remarkably dense in the posterior magnocellular division of the paraventricular nucleus, especially in the dorso-lateral portion where vasopressin-containing cells predominate. Noradrenergic fiber input to these magnocellular neurons is likely since phenylethanolamine-N-methyltransferase-immunostained fibers are sparse in magnocellular subnuclei of the paraventricular nucleus. Dual immunocytochemical staining of thick and thin tissue sections demonstrates with clarity an anatomical association of dopamine -hydroxylase-immunostained fibers and magnocellular neurons. Dopamine -hydroxylase-immunostained and phenylethanolamine-N-methyltransferase-immunostained fibers are dense in the medial parvocellular component of the paraventricular nucleus; distinct features of both antisera are presented.     

Profound contrast adaptation early in the visual pathway

Prior exposure to a moving grating of high contrast led to a substantial and persistent reduction in the contrast sensitivity of neurons in the lateral geniculate nucleus (LGN) of macaque. This slow contrast adaptation was potent in all magnocellular (M) cells but essentially absent in parvocellular (P) cells and neurons that received input from S cones. Simultaneous recordings of M cells and the potentials of ganglion cells driving them showed that adaptation originated in ganglion cells. As expected from the spatiotemporal tuning of M cells, adaptation was broadly tuned for spatial frequency and lacked orientation selectivity. Adaptation could be induced by high temporal frequencies to which cortical neurons do not respond, but not by low temporal frequencies that can strongly adapt cortical neurons. Our observations confirm that contrast adaptation occurs at multiple levels in the visual system, and they provide a new way to reveal the function and perceptual significance of the M pathway.     

Cone connections of the horizontal cells of the rhesus monkey's retina

The presence in the rhesus monkey's retina of a second morphological type of horizontal cell (H2), described by Kolb et al. (1980), is confirmed. Both types of cell are here further described. Their cone connections are quantified and compared with those of mammals and other vertebrates. The dendrites and axons of the H2 type of cell contact only cones as do the dendrites of the H1 cell (originally described by Polyak (1941)) which has an axon contacting only rods. The dendrites of foveal H2 cells contact between 11 and 14 cones; those of H1 contact 7. The number of cones that each type of cell contacts increases with increasing distance from the fovea, so that, by 5-6 mm eccentricity, H2-type cells synapse with between 20 and 30 cones, and the H1 cells with 12-15. The qualitatively estimated coverage factors of each are 3 or 4; every cone synapses with more than one of both types. Neither type of horizontal cell makes chromatically specific connections that are anatomically recognizable, unlike the situation in some teleostean and turtle retinae. Individual horizontal cells, particularly those connected to foveal cones, may have different ratios of chromatic input. At equivalent eccentricities, up to about 6 mm from the fovea, the dendritic fields of H2 horizontal cells are about twice the size of H1 cells and contact about twice the number of cones. These relative differences are closely similar to those of the cat's horizontal cells and it is suggested that they are a basic feature of most placental mammals. The organization of foveal cone fibres within Henle's layer is described. The distribution of primate cone telodendria, gap junctions and synapses in the outer plexiform layer are briefly reviewed and compared with those of other vertebrate retinae.     

A simple model of human foveal ganglion cell responses to hyperacuity stimuli

We developed a physiologically plausible model of the first steps of spatial visual information processing in the fovea of the human retina. With the predictions of this model we could support the hypothesis that, for moderate contrasts ( 40%), hyperacuity is mediated by the magnocellular (MC-) pathway. Despite the lower sampling density in the MC pathway, as compared to the parvocellular (PC-) pathway, the information that is transferred by the MC ganglion cells is sufficient to achieve thresholds comparable to those of human subjects in psychophysical tasks. This is a result of the much higher signal-to-noise ratio of the MC pathway cell signals. The PC pathway cells do not transfer enough information for hyperacuity thresholds.     

Dynamics of the cone-horizontal cell circuit in the turtle retina

The model of the catfish retina (Siminoff, in press) has been extended to the turtle retina with incorporation of color-coding. The turtle retina contains 6 types of cones of which 4 are red-sensitive and the other 2 are green-and blue-sensitive, respectively. The cone-horizontal circuit incorporates negative feedback from the L-HC to all the cones having input to the L-HC. By use of systems analysis, Laplace transforms and the convolution theorem, impulse responses, that give information as to gain and phase, for the cone-types and L-HC were simulated. As with the catfish retina, negative feedback gain was proportional to the dc level of the L-HC and therefore, the mean illuminance level. It was shown that this mechanism can be an important factor in chromatic adaptation, since the gains of the various cone-types are preferentially altered dependent on mean illuminance level and wavelength of the background light.     

On optical receivers in the pathway implicated in regulating the human circadian rhythm

Biological and mathematical grounding was provided for the mechanism that is responsible for the optical radiation-dependent regulation of the human circadian rhythm that involves the well-known retinal photoreceptors, rods and blue-sensitive cones. It was shown that light-sensitive retinal ganglion cells are unable to act as receivers of optical radiation. Two spectral channels involved in regulating the circadian rhythm were observed in the retino-hypothalamic pathway. An analytical expression for the function of the relative spectral circadian efficiency was obtained for Scalculations and mathematical modeling of the human circadian rhythm.

     

Evidence for the presence of nerve growth factor (NGF) and NGF receptors in human testis

Summary The co-localization of arginine vasopressin-and enkephalin-like immunoreactivities in nerve cells of the rat paraventricular hypothalamic nucleus and adjacent areas was investigated by the simultaneous application of immuno--galactosidase staining and the peroxidase-antiperoxidase method to sections. Arginine vasopressin-like immunoreactive cells were stained blue with immuno--galactosidase staining and enkephalin-like immunoreactive cells brown with the peroxidase-antiperoxidase method. Double-labeled cells with overlap of blue and brown immunoreaction products were identified in the anterior, medial, and lateral parvocellular parts of the paraventricular hypothalamic nucleus as well as in the previously indicated posterior magnocellular part. Other regions that contained double-labeled cells were the lateral hypothalamic area, anterior hypothalamic nucleus, area between the lateral hypothalamic area and anterior hypothalamic nucleus, suprachiasmatic nucleus, and bed nucleus of the stria terminalis, medial division, posterolateral part. These findings suggest that nerve cells with both arginine vasopressin- and enkephalin-like immunoreactivities may be more actively involved in neuroendocrine regulation and neural transmission than previously considered. They may provide a morphological basis for an increase in enkephalin-like immunoreactivity within the anterior pituitary in cases of hemorrhagic shock which is presumably accompanied by arginine vasopressin hypersecretion.Abbreviations AH anterior hypothalamic nucleus - ap anterior parvocellular part of the paraventricular hypothalamic nucleus - BSTMPL bed nucleus of the stria terminalis, medial division, posterolateral part - dp dorsal parvocellular part of the paraventricular hypothalamic nucleus - f fornix - LH lateral hypothalamic area - lp lateral paryocellular part of the paraventricular hypothalamic nuclcus - mp medial parvocellular part of the paraventricular hypothalamic nucleus - MPA medial preoptic area - pm posterior magnocellular part of the paraventricular hypothalamic nucleus - pv periventricular part of the paraventricular hypothalamic nucleus - SC suprachiasmatic nucleus - Zi zona incerta     

Electronic simulation of ganglion cells of generalized vertebrate cone retina

Electronic simulation of generalized vertebrate cone retina consists of 43x41 grid of red-, green-, and blue-sensitive cones. Each retinal element is simulated by a linear summator in series with a leaky integrator and spatial-temporal properties are developed by spatial organization of cone mosaic into unit hexagons and interplay of antagonistic inputs of differing time courses. Model has full compliments of horizontal and bipolar cells including color- and noncolor coding as well as single- and double-opponent receptive fields for bipolar cells. Electronic simulation also has negative feedback from L-horizontal cells to cones. Ganglion cells are formed by convergence of 7 bipolar cells, either all same and thus homogeneous, or else with a central-DPBC (or HPBC) and 6 surround-HPBCs (or DPBCs) and thus non-homogeneous. Responses of color- and non-color-coded ganglion cells as well as single- and double-opponents are investigated with stationary and moving light spots using white and colored lights. While responses to stationary light spots are predictable from digital models, responses to moving spots are complicated by differing time lags of components involved in total response. Therefore, responses to moving stimuli are more readily simulated by analogue models.     

In situ hybridization of corticotropin-releasing factor-encoding messenger RNA in the hypothalamus of the white sucker,Catostomus commersoni

Summary In situ hybridization procedure with a ³²P-labelled synthetic oligonucleotide probe was used to detect corticotropin-releasing factor-encoding messenger RNA (CRF mRNA) in the hypothalamus of the white sucker, Catostomus commersoni. Adjacent sections were immunostained by a sucker CRF-specific antiserum. CRF mRNA-containing neurons were identified by autoradiography in the magnocellular and parvocellular subdivisions of the preoptic nucleus (PON). Many of these neurons were also immunostained by sucker antiserum, showing the same distribution patterns. These results confirm the presence of CRF mRNA and CRF peptide in the white sucker hypothalamus and support the view that the magnocellular and parvocellular neurons of the PON may be involved in the control of adrenocorticotropic hormone secretion from the pituitary in the white sucker.     

Electronic simulation of cones,horizontal cells and bipolar cells of generalized vertebrate cone retina

Electronic analogue of my theoretical model of generalized vertebrate cone retina [Siminoff: J. Theor. Biol. 86, 763 (1980)] is presented. Cone mosaic is simulated by 25x21 grid of phototransistors that have colored filters mounted in front of then to produce red-, green-, and blue-sensitive cones arranged in a trichromatic retina. Each retinal element is simulated by Summator-Integrator and unit gain voltage invertes are used to give correct polarities to output voltages. Dynamic properties of retinal elements are developed solely by temporal interplay of antagonistic input voltages with differing time courses, and spatial organization of receptive fields is developed by unit hexagons that precisely define cone input voltages to subsequent elements. Electronic model contains both color- and non-colorcoded channels. Negative feedback from L-horizontal cells to cones, electrical coupling of like-cones, and electrical coupling of like-horizontal cells are simulated by feedfoward circuits. Stray light is present due to light scattering properties of colored filters used to simulate color selectivety of cones. Stationary and moving spots of white and colored lights of varied sizes and intensities are used to study characteristics of electronic analogue. Results demonstrate practicality of electronic simulation to function analogous to real cone retinas to process visual stimuli and give information to higher centers as to size, shape, color and motion of objects in visual world.     

Axonal outgrowth within the abnormal scaffold of brain tracts in a zebrafish mutant

The role of specific axonal tracts for the guidance of growth cones was investigated by examining axonal outgrowth within the abnormal brain tracts of zebrafish cyclops mutants. Normally, the earliest differentiating neurons in the zebrafish brain establish a simple scaffold of axonal tracts. Later-developing axons follow cell-specific pathways within this axonal scaffold. In Cyclops embryos, this scaffold is perturbed due to the deletion of some ventromedial neurons that establish parts of the axonal scaffold and the development of an abnormal crease in the brain. In these mutant embryos, the growth cones projected by the neurons of the nucleus of the posterior commissure (nur PC) are deprived of the two tracts of axons that they sequentially follow to first extend ventrally, then posteriorly. These growth cones respond to the abnormal scaffold in several interesting ways. First, nuc PC growth cones initially always extend ventrally as in wild-type embryos. This suggests that for the first portion of their pathway the axons they normally follow are not required for proper navigation. Second, approximately half of the nuc PC growth cones follow aberrant longitudinal pathways after the first portion of their pathway. This suggests that for the longitudinal portion of the pathway, specific growth cone/axon interactions are important for guiding growth cones. Third, although approximately half of the nuc PC growth cones follow aberrant longitudinal pathways, the rest follow normal pathways despite the absence of the axons that they normally follow. This suggests that cues independent of these axons may be capable of guiding nuc PC growth cones as well. These results suggest that different guidance cues or combinations of cues guide specific growth cones along different portions of their pathway. 1994 John Wiley & Sons, Inc.     

The role ofc-type cytochromes in the terminal respiratory chain of the methylotrophic bacteriumMethylophilus methylotrophus

Whole cells of the methylotrophic bacteriumMethylophilus methylotrophus cultured under methanol-limited conditions contain approximately equal amounts of two majorc-type cytochromes,c _H andc _L. Virtually all of the cytochromec _H, and over one-third of the cytochromec _L, are loosely attached to the periplasmic surface of the respiratory membrane whence they can be released by sonication or by washing cells in ethylenediaminetetraacetate (EDTA). The latter causes inhibition of methanol oxidase activity and stimulation of ascorbate-N,N,N,N-tetramethyl-p-phenylenediamine (TMPD) oxidase activity, neither of which effects are reversible by divalent metal ions. Kinetic analyses indicate that ascorbate-TMPD is oxidised via two routes, viz. a slow low-affinity pathway involving loosely membrane-boundc-type cytochromes plus cytochrome oxidaseaa ₃, and a faster higher-affinity pathway involving the firmly membrane-bound cytochrome oxidasec _L o complex; the former route predominates in the presence of divalent metal ions, and the latter route after exposure to EDTA. These and other results are discussed in terms of the spatial organisation of the terminal respiratory chain, and of the role ofc-type cytochromes in the oxidation of methanol and ascorbate-TMPD.Abbreviations EDTA Enthylenediaminetetraacetate - PMS Phenazinemethosulphate - TMPD N,N,N,N-tetramethyl-p-phenylenediamine - SDS Sodium dodecylsulphate - I₅₀ Concentration of inhibitor required to give 50% inhibition of enzyme activity - PQQ Pyrroloquinoline quinone     

Microtubule-associated protein 2 (MAP2)-immunoreactive neurons in the retina of Bufo marinus: colocalisation with tyrosine hydroxylase and serotonin in amacrine cells

Summary Neuron populations in the retina of the toad, Bufo marinus, were labelled with a monoclonal antibody raised against microtubule-associated protein 2 (MAP2). A subpopulation of cones, probably corresponding to the blue-sensitive small single cones, large diameter amacrine cells in the most proximal row of the inner nuclear layer and some large ganglion cells in the ganglion cell layer were labelled. Double labelling experiments were carried out to establish the colocalisation of MAP2 with known putative transmitter substances of the anuran amacrine cells. MAP2 was colocalised in a subpopulation of serotonin-immunoreactive and in all tyrosine hydroxylase-immunoreactive amacrine cells. The results indicate, that the MAP2 content in the neurons of the anuran retina can be correlated with other well-defined neurochemical and/or physiological properties.On leave from Department of Zoology, Attlia József University, Szeged, Hungary     

Ganglion Cell and Displaced Amacrine Cell Density Distribution in the Retina of the Howler Monkey (Alouatta caraya)

Unlike all other New World (platyrrine) monkeys, both male and female howler monkeys (Alouatta sp.) are obligatory trichromats. In all other platyrrines, only females can be trichromats, while males are always dichromats, as determined by multiple behavioral, electrophysiological, and genetic studies. In addition to obligatory trichromacy, Alouatta has an unusual fovea, with substantially higher peak cone density in the foveal pit than every other diurnal anthropoid monkey (both platyrrhines and catarrhines) and great ape yet examined, including humans. In addition to documenting the general organization of the retinal ganglion cell layer in Alouatta, the distribution of cones is compared to retinal ganglion cells, to explore possible relationships between their atypical trichromacy and foveal specialization. The number and distribution of retinal ganglion cells and displaced amacrine cells were determined in six flat-mounted retinas from five Alouatta caraya. Ganglion cell density peaked at 0.5 mm between the fovea and optic nerve head, reaching 40,700–45,200 cells/mm². Displaced amacrine cell density distribution peaked between 0.5–1.75 mm from the fovea, reaching mean values between 2,050–3,100 cells/mm². The mean number of ganglion cells was 1,133,000±79,000 cells and the mean number of displaced amacrine cells was 537,000±61,800 cells, in retinas of mean area 641±62 mm². Ganglion cell and displaced amacrine cell density distribution in the Alouatta retina was consistent with that observed among several species of diurnal Anthropoidea, both platyrrhines and catarrhines. The principal alteration in the Alouatta retina appears not to be in the number of any retinal cell class, but rather a marked gradient in cone density within the fovea, which could potentially support high chromatic acuity in a restricted central region.     

Survival associated pathway identification with group <Emphasis Type="Italic">L</Emphasis><Subscript><Emphasis Type="Italic">p</Emphasis></Subscript> penalized global AUC maximization

It has been demonstrated that genes in a cell do not act independently. They interact with one another to complete certain biological processes or to implement certain molecular functions. How to incorporate biological pathways or functional groups into the model and identify survival associated gene pathways is still a challenging problem. In this paper, we propose a novel iterative gradient based method for survival analysis with group L _p penalized global AUC summary maximization. Unlike LASSO, L _p (p < 1) (with its special implementation entitled adaptive LASSO) is asymptotic unbiased and has oracle properties [1]. We first extend L _p for individual gene identification to group L _p penalty for pathway selection, and then develop a novel iterative gradient algorithm for penalized global AUC summary maximization (IGGAUCS). This method incorporates the genetic pathways into global AUC summary maximization and identifies survival associated pathways instead of individual genes. The tuning parameters are determined using 10-fold cross validation with training data only. The prediction performance is evaluated using test data. We apply the proposed method to survival outcome analysis with gene expression profile and identify multiple pathways simultaneously. Experimental results with simulation and gene expression data demonstrate that the proposed procedures can be used for identifying important biological pathways that are related to survival phenotype and for building a parsimonious model for predicting the survival times.     

Two different electron transfer pathways may involve in azoreduction in Shewanella decolorationis S12

Electron transfer pathways for azoreduction by S. decolorationis S12 were studied using a mutant S12-22 which had a transposon insertion in ccmA. The results imply that there are two different pathways for electron transport to azo bonds. The colony of S12-22 was whitish and incapable of producing mature c-type cytochromes whose α-peak was at 553 nm in the wild type S12. The mutant S12-22 could not use formate as the sole electron donor for azoreduction either in vivo or in vitro, but intact cells of S12-22 were able to reduce azo dyes of low polarity, such as methyl red, when NADH was served as the sole electron donor. Although the highly polar-sulfonated amaranth could not be reduced by intact cells of S12-22, it could be efficiently reduced by cell extracts of the mutant when NADH was provided as the sole electron donor. These results suggest that the mature c-type cytochromes are essential electron mediators for the extracellular azoreduction of intact cells, while the other pathway without the involvement of mature c-type cytochromes, NADH-dependent oxidoreductase-mediated electron transfer pathway can reduce lowly polar sulfonated azo dyes inside the whole cells or highly polar sulfonated azo dyes in the cell extracts without bacterial membrane barriers.     

Vasopressin and oxytocin in the neural control of the circulation

Catecholamine innervation originating in dorsal medial and ventral lateral medulla terminates on parvocellular and magnocellular subnuclei, respectively, of the paraventricular nucleus of the hypothalamus. In turn, parvocellular pathways terminate in brain stem and spinal cord, whereas magnocellular pathways terminate in median eminence and posterior pituitary. Consistent with the neuroanatomy, we find that baroreceptor regulation of neuroendocrine (plasma vasopressin) and autonomic (blood pressure) functions can be dissociated. Further, studies indicate that sympathetic vasomotor pathways are activated by injections of vasopressin and oxytocin into the nucleus tractus solitarii and vasopressin into the lateral cerebral ventricles. Also, parasympathetic pathways to the heart and baroreflex function are activated and augmented, respectively, by i.v. administered vasopressin. These results are consistent with at least three central sites of action and suggest a complex role of vasopressin (and possibly oxytocin) in the central neural regulation of the heart and circulation.