bluuebunny/crossref_metadata_2025 huggingface dataset:
Enkephalin-immunoreactive ganglion cells in the pigeon retina
Authors: Britto Luiz R. G. , Hamassaki-Britto Dȃnia E.
Published: June 2009

A small number of enkephalin-like immunoreactive cells were observed in the ganglion cell layer of the pigeon retina. Many of these neurons were identified as ganglion cells, since they were retrogradely labeled after injections of fluorescent latex microspheres in the contralateral optic tectum. These ganglion cells were mainly distributed in the inferior retina, and their soma sizes ranged from 12–26 μm in the largest axis. The enkephalin-containing ganglion cells appear to represent only a very small percentage of the ganglion cells projecting to the optic tectum (less than 0.1%). Two to 7 weeks after removal of the neural retina, there was an almost complete elimination of an enkephalin-like immunoreactive plexus in layer 3 of the contralateral, rostrodorsal optic tectum. These data provide evidence for the existence of a population of enkephalinergic retinal ganglion cells with projections to the optic tectum.
Area 17 lesions deactivate area MT in owl monkeys
Authors: Kaas Jon H. , Krubitzer Leah A.
Published: June 2009

The middle temporal visual area, MT, is one of three major targets of the primary visual cortex, area 17, in primates. We assessed the contribution of area 17 connections to the responsiveness of area MT neurons to visual stimuli by first mapping the representation of the visual hemifield in MT of anesthetized owl monkeys with microelectrodes, ablating an electrophysiologically mapped part of area 17, and then immediately remapping MT. Before the lesions, neurons at recording sites throughout MT responded vigorously to moving slits of light and other visual stimuli. In addition, the relationship of receptive fields to recording sites revealed a systematic representation of the contralateral visual hemifield in MT, as reported previously for owl monkeys and other primates. The immediate effect of removing part of the retinotopic map in area 17 by gentle aspiration was to selectively deactivate the corresponding part of the visuotopic map in MT. Lesions of dorsomedial area 17 representing central and paracentral vision of the lower visual quadrant deactivated neurons in caudomedial MT formerly having receptive fields in the central and paracentral lower visual quadrant. Most neurons at recording sites throughout other parts of MT had normal levels of responsiveness to visual stimuli, and receptive-field locations that closely matched those before the lesion. However, neurons at a few sites along the margin of the deactivated zone of cortex had receptive fields that were slightly displaced from the region of vision affected by the lesion into other parts of the visual field, suggesting some degree of plasticity in the visual hemifield representation in MT. Subsequent histological examination of cortex confirmed that the lesions were confined to area 17 and the recordings were in MT. The results indicate that the visually evoked activity of neurons in MT of owl monkeys is highly dependent on inputs relayed directly or indirectly from area 17.
Neuronal basis for parallel visual processing in the fly
Authors: Strausfeld Nicholas J. , Lee Jong-Kyoo
Published: June 2009

Behavioral and electrophysiological studies of insects demonstrate both spectrally independent and chromatically dependent behaviors and interneurons. This account describes the neuroanatomical identification of two parallel retinotopic subsystems, one supplying descending channels to spectrally independent neck and flight motor circuits, the other supplying polychromatic channels to neuropils associated with leg motor circuits in the thoracic ganglia. In the compound eye, two classes of photoreceptors contribute to each of several thousand sampling units. High-sensitivity, chromatically uniform short-axon photoreceptors (R1-R6) supply the lamina's external plexiform layer and are presynaptic to L1, L2 efferents. These project in parallel with a second system of trichromatic long-axon receptors and the L3 efferent. Both pathways supply columns of the medulla, equal in number to ommatidia. Golgi and cobalt-silver impregnation demonstrates that neurons from the medulla diverge to two deeper regions, the lobula plate and lobula, the former a thin tectum of neuropil dorsal to the more substantial lobula. Layer relationships between medulla neurons and their afferent supply suggest that the lobula plate and lobula are each supplied by one or the other, but not both, of the two parallel subsystems. Independence of the two parallel pathways is suggested by ablation of the photoreceptor layer leading to selective degeneration of the motion-sensitive lobula plate neuropil. In addition, octets of small-field neurons associated with the R1-R6/L1, L2 pathway give rise to synaptic complexes with motion-sensitive neurons of the lobula plate. A variety of behavioral and electrophysiological studies provide supporting evidence that certain insects possess parallel visual pathways comparable to the magnocellular and parvocellular subsystems of primates.
Induction of retinal degeneration in a crab by light and okadaic acidin vitro: Comparison with theDrosophilalight-dependent retinal degeneration mutantw rdgBKS222
Authors: Blest A. D. , Carter M. , Clausen J. A. , Stowe S. , Trowell S. C. , Tsukitani Y.
Published: June 2009

Retinae of the crabLeptograpsuswhich had been maintained on a 12-h light/12-h dark cycle were culturedin vitroand exposed to 1 μM okadaic acid (OKA) at 0.75 h before light onset. Control retinae were subjected to the same routine and sampled at the same times without OKA treatment. At the concentration used, OKA totally inhibits types 1 and 2A protein phosphatases, minimally inhibits type 2B, and does not affect type 2C. 1 μM OKA provoked a diminution of rhabdom diameter measured at the level of the photoreceptor nuclei in the dark, some ommatidial cartridges being stripped of rhabdomeral microvilli altogether. After 1-h illumination (225–320 lux), further reduction of rhabdom diameter was modest in control retinae but precipitate in those treated with OKA. After 2 h, control rhabdom diameters showed a further, not significant, decline, but OKA had induced a resynthesis of massive structures with the light-microscopic appearance of rhabdoms. Electron microscopy revealed that they were heterogeneous and of the following kinds: (1) a minority of rhabdoms with normally disposed but distorted microvilli; (2) rhabdoms in the throes of events that parody normal assembly; and (3) rhabdomal volumes occupied by saccular organelles or by pleats or ruffles of irregular architecture. The cytoplasm of all such receptors was packed with free and bound ribosomes and endomembranes. The sequence of events parallels that seen during light-induced degeneration of photoreceptors of theDrosophilamutantw rdgBKS222. Preliminary experiments show that a protein kinase activator SC-9 mimics many of these effects in the dark in the presence of 1 μM OKA. As a working hypothesis, it is proposed that light activates protein kinasesviadiacylglycerols generated by the phototransduction cascade, and that in both crab retinas challenged with OKA and retinas ofrdgBKS222activation of a nuclear regulatory protein by hyperphosphorylation provokes a runaway transcription whose selectivity and extent remain to be determined.
Anatomical pathways for color vision in the human retina
Authors: Kolb Helga
Published: June 2009

The major neurons and neural circuits that are involved in the transmission of color signals through the human retina to produce the color and spatially opponent P cell or midget ganglion cell responses are described. The older findings of single cone to midget bipolar connectivity is reviewed, and the single midget bipolar cell to midget ganglion cell connectivity as revealed by a recent serial section electron microscope study is described in detail. Our present knowledge concerning the discrimination of the blue-cone subtype from the other longer wavelength cones in the human at the outer plexiform layer is summarized, and our most recent findings concerning horizontal cell connectivity to the different spectral types of cones are discussed. Finally, a hypothetical pathway is proposed for color-opponent surrounds of midget ganglion cells using both horizontal cells at the outer plexiform layer and amacrine cell pathways at the inner plexiform layer.
Red-green interactions in the spectral sensitivity of primates as derived from ERG and behavioral data
Authors: Sperling Harry G. , Mills Stephen L.
Published: June 2009

Different techniques were used to manipulate the inhibitory interaction between the red and green photoreceptors (R and G cones) of rhesus and human primates. The response techniques that were used were the corneal electroretinogram (ERG) and psychophysical increment-threshold spectral sensitivity functions. Red-green opponency, as measured by the depth of the notch at 580 nm, is removed by intravitreal injection of bicuculline but not by strychnine. Therefore, red-green opponency is mediated by GABA and not glycine. The depth of the notch is dependent upon stimulus size. Between 30' and 15' test light diameters, this sign of red-green opponency disappears. Psychophysical increment thresholds are shown to produce the notch while decrements do not and intravitreal APB is shown to reduce the notch, evidence that red-green opponency is carried by the “ON” and not the “OFF” bipolar pathways of the retina. Red and green annuli are shown to selectively reduce red and green inhibition, as though there were selective reduction of the surround response in center-surround organized red-green receptive fields.
Retinal neuromodulation: The role of dopamine
Authors: Dowling John E.
Published: June 2009

Dopamine exerts multiple effects on retinal horizontal cells. Dopamine, via cyclic AMP and protein kinase A, reduces the light responsiveness of horizontal cells and the electrical coupling between the cells. The gating kinetics of both gap-junctional and glutamate channels are altered as a result of phosphorylation by protein kinase A. Dopamine also causes a reversible retraction of neurites of horizontal cells maintained in culture. Diacylglycerol analogues as well as phorbol esters mimic this effect of dopamine, but not cyclic AMP analogues or Forskolin. The results suggest that dopamine causes neurite retraction by the activation of protein kinase C via diacylglycerol.
The rod bipolar cell of the mammalian retina
Authors: Wässle Heinz , Yamashita Masayuki , Greferath Ursula , Grünert Ulrike , Müller Frank
Published: June 2009

Three approaches to study the function of mammalian rod bipolar cells are described. Extracellular recordings from the intact cat eye under light- and dark-adapted conditions showed that in dark-adapted retina all light responses can be blocked by 2-amino-4-phosphonobutyrate (APB). Immunocytochemical staining with an antibody against protein kinase C (PKC) labeled rod bipolar cells in all mammalian retinae tested. When rat retinae were dissociated, PKC immunoreactivity was also found in isolated bipolar cells and could be used for their identification as rod bipolars. Patch-clamp recordings were performed from such dissociated rod bipolar cells and their responses to APB were measured. APB closed a nonselective cation channel in the cell membrane. The actions of GABA and glycine were also tested and both opened chloride channels in dissociated rod bipolar cells. These results suggest that rod bipolar cells are depolarized by a light stimulus and that GABA as well as glycine modulate their light responses.
The organization of dopaminergic neurons in vertebrate retinas
Authors: Witkovsky Paul , Schütte Michael
Published: June 2009

A survey of the shapes of dopaminergic (DA) neurons in the retinas of representative vertebrates reveals that they are divisible into three groups. In teleosts and Cebus monkey, DA cells are interplexiform (IPC) neurons with an ascending process that ramifies to create an extensive arbor in the outer plexiform layer (OPL). All other vertebrates studied, including several primate species, have either DA amacrine cells or IPCs with an ascending process that either does not branch within the OPL or does so to a very limited degree. DA neurons of non-teleosts exhibit a dense plexus of fine caliber fibers which extends in the distal most sublamina of the inner plexiform layer (IPL). Teleosts lack this plexus. In all vertebrates, DA cells are distributed more or less evenly and at a low density (10–60 cells/mm2) over the retinal surface. Dendritic fields of adjacent DA neurons overlap. Most of the membrane area of the DA cell is contained within the plexus of fine fibers, which we postulate to be the major source of dopamine release. Thus, dopamine release can be modeled as occurring uniformly from a thin sheet located either in the OPL (teleosts) or in the distal IPL (most other vertebrates) or both (Cebus monkey). Assuming that net lateral spread of dopamine is zero, the fall of dopamine concentration with distance at right angles to the sheet (i.e. in the scleral-vitreal axis) will be exponential. The factors that influence the rate of fall – diffusion in extracellular space, uptake, and transport – are not yet quantified for dopamine, hence the dopamine concentration around its target cells cannot yet be assessed. This point is important in relation to the thresholds for activation of D1 and D2 dopamine receptors that are found on a variety of retinal cells.
Some visual and neurochemical correlates of refractive development
Authors: Laties Alan M. , Stone Richard A.
Published: June 2009

Increasing evidence indicates that the retina takes part in the postnatal regulation of eye growth, functioning in this respect to minimize refractive error. The evidence derives both from clinical observations in man and from experiments in animals. The discovery that visual form deprivation leads to an axial overgrowth of the eye and to myopia has opened the way to many current research initiatives. Neurochemical and immunocytochemical experiments in chick and monkey suggest that definable retinal neurons participate in the regulatory pathway controlling eye growth. The most comprehensive data presently implicate dopaminergic amacrine cells. Other important issues to be addressed include the relevance of an intact connection to the central nervous system and the precise retinal mechanism by which eye growth is regulated.
An enzymatically enhanced recording technique forLimulusventral photoreceptors: Physiology, biochemistry, and morphology
Authors: Zhang Hui-Juan , Jinks Robert N. , Wishart Anne C. , Battelle Barbara-Anne , Chamberlain Steven C. , Fahrenbach Wolf H. , Kass Leonard
Published: June 2009

Enzymatic treatments that facilitated whole-cell electrophysiological recordings were used onLimulusventral photoreceptor cells. Ventral optic nerves were treated with either collagenase or collagenase, papain, and trypsin. Either treatment greatly increased the ease of making whole-cell recordings of transmembrane potentials. Light responses obtained from enzyme-treated photoreceptor cells were nearly identical to results obtained without enzyme treatment and compared favorably toin vivorecordings of light responses from the compound lateral eye. Enzyme-treated cells also responded to applied octopamine, as do untreated cells, with an increased phosphorylation of a 122-kD protein. This suggests that the external receptors and internal biochemical machinery required for at least one second-messenger cascade are present after enzyme treatment. The morphological integrity of enzyme-treated photoreceptor cells was examined with light microscopy as well as with scanning and transmission electron microscopy. In general, we found that each enzyme treatment greatly reduced the integrity of the layers of glial cells that surround the photoreceptor cells thereby making these cells easily accessible for whole-cell recordings of transmembrane potentials. The morphology of the rhabdomere was normal after enzymatic degradation of the adjacent glial covering.
Bipolar cells of the chick retina containing α-bungarotoxin-sensitive nicotinic acetylcholine receptors
Authors: Hamassaki-Britto Dânia E. , Brzozowska-Prechtl Agnieszka , Karten Harvey J. , Lindstrom Jon M.
Published: June 2009

Two cDNA clones for nicotinic acetylcholine receptor (nAChR) subunits sensitive to α-bungarotoxin (α-Bgt) have been isolated, the so-called α-Bgt binding proteins α1 (or α7 nAChR subunit) and α2 (or α8 nAChR subunit). Immunohistochemical experiments have shown that both α7 and α8 subunits, as well as subunits insensitive to α-Bgt (β2 and α3), are present in amacrine and ganglion cells of the chick retina. However, only the α8 subunit was observed in presumptive bipolar cells. The present study investigated in detail the pattern of distribution of the bipolar cells containing the α8 nAChR subunit and its relation to the pattern of distribution of bipolar cells immunoreactive to protein kinase C (PKC). Presumptive α8-and PKC-like immunoreactive (α8-LI and PKC-LI) bipolar cells were observed sending their dendrites to the outer plexiform layers and their axons to the inner plexiform layer. Where as α8-LI bipolar cells corresponded to 40–53% of the whole population of bipolar cells, PKC-LI bipolar cells represented only 6–8% of the same population. The soma sizes of the α8-LI bipolar cells were slightly smaller (mean ± s.d.; 4.9 ± 0.8 μm) than the soma sizes of the PKC-LI bipolar cells (5.4 ± 0.9 μm). Double-labeling experiments indicated that probably all PKC-LI bipolar cells also contain α8-LI. This indicates that two distinct groups of cholinoceptive bipolar cells exist in the chick retina, one that contains PKC-LI, and another one that does not.
The postnatal development of geniculocortical axon arbors in owl monkeys
Authors: Pospichal Marcie W. , Florence Sherre L. , Kaas Jon H.
Published: June 2009

To characterize the postnatal development of geniculocortical axon arbor morphology in owl monkeys at a series of ages from birth to adulthood, individual arbors were bulk-filled with HRP in brain slice preparations and were reconstructed from serial sections. At all ages, cortical layers and sublayers were obvious. Presumed M or magnocellular arbors were largely confined to layer IVα, but they also extended into layer IIIc (IVB of Brodmann, 1909); presumed P or parvocellular arbors were almost exclusively confined to layer IVβ. Other axons that may reflect feedback projections from MT terminated in layer IIIc. Overall, M axon arbors increased in size and complexity from birth to adulthood with mean surface-view arbor areas ranging from 0.08 ± 0.01 mm2 in newborns to 0.24 ± 0.02 mm2 in adults. The developing P arbor areas were, on average, as large or larger than adult (newborn = 0.07 ± 0.01 mm2, adult = 0.047 ± 0.01 mm2; n.s.) but the arbors were somewhat less complex. Since the brain and area 17 increase in size postnatally, the proportion of area 17 subserved by each P arbor would decrease in postnatal development. Terminal boutons with immature features were evident in both M and P populations at all developmental ages. The results indicate that, while both LGN axon types in monkeys undergo morphological changes postnatally, M arbors appear to mature by increasing arbor size and terminal branching complexity, whereas P arbors increase in complexity but not in size. These distinct programs of axon arbor development suggest that the periods of susceptibility of geniculocortical axon arbors to postnatal influences of the environment, and the types of plastic responses they potentially exhibit, are class-specific.
Opponent-color detection threshold asymmetries may result from reduction of ganglion cell subpopulations
Authors: Billock Vincent A. , Vingrys Algis J. , King-Smith P. Ewen
Published: June 2009

Thresholds for psychophysically opposite stimuli—light and dark, or equiluminous red and green, or equiluminous blue and yellow—are usually nearly equal. This color threshold symmetry is sometimes violated in subjects who have optic nerve hypoplasia, a congenital loss of retinal ganglion cells. We describe a subject who has optic nerve hypoplasia, who exhibits large red-green and blue-yellow detection threshold asymmetries for equiluminous spots. Temporal and spatial integration for equiluminous red and green test spots also differed from normal; static perimetric thresholds for equiluminous green, blue, and yellow (but not red) spots lacked the normal “V” shaped minimum at the fovea. These asymmetries may relate to a developmental paucity of some ganglion cell subtypes. Optic nerve hypoplasia may allow the contributions to detection made by individual ganglion cell subtypes to be isolated psychophysically, in analogy to the study of cone spectral sensitivity in dichromats.
Cortical projections to anterior inferior temporal cortex in infant macaque monkeys
Authors: Rodman Hillary R. , Consuelos Michael J.
Published: June 2009

Inferior temporal (IT) cortex is a “high-order” region of extrastriate visual cortex important for visual form perception and recognition in adult primates. The pattern of cortical afferents from both ipsilateral and contralateral hemispheres to anterior IT cortex was determined in infant macaque monkeys 7–18 weeks of age following injections of wheat-germ agglutinin-HRP. Within the ipsilateral hemisphere, the locations and laminar distribution of labeled cells were similar to those observed after comparable injections in adult monkeys. Specifically, ipsilateral afferents derived from visual areas V4, TEO, anterior and posterior IT, and STP, from parahippocampal, perirhinal, and parietal zones, and from several anterior zones including lateral and ventral frontal cortex, the insula, and cingulate cortex. Within the contralateral hemisphere, we observed labeled cells in homotopic regions of IT and in parahippocampal and perirhinal areas, as has been reported for adult monkeys. However, we also identified additional contralateral regions not previously known to provide input to anterior IT, including lateral and ventral frontal cortex, cingulate cortex, and STP. Overall, the strongest and most widespread projections from outside the temporal lobe were found in the youngest monkey, suggesting that some of these projections may represent transient circuitry necessary for the development of complex visual response properties in anterior IT.
Variability of responses to sinusoidal modulation
Authors: Levine Michael W.
Published: June 2009

Many studies of visual neurons make use of stimuli that are sinusoidally modulated in time, and take as the response the fundamental Fourier component of the firing. This is a study of the variability of the fundamental sinusoidal components.

A theoretical analysis shows that the variance of sinusoidal components should be nearly independent of their amplitudes; this is expected despite the observation that variance of firing rate increases with increasing firing rate. However, this result applies only to the variance of the complex amplitude, defined as the complex Fourier amplitude in response to each stimulus cycle. This variance is called the complex variance. The variance of the scalar amplitude, which is simply the amplitude in response to each stimulus cycle disregarding phase (scalar variance) is expected to shrink by a factor of up to 2⅓ as the response magnitude approaches zero.

If the relationship between variance of rate and rate is linear, complex variance should be independent of amplitude. If the relationship between variance of rate and rate is characterized by a compressive nonlinearity (as has been observed), the complex variance should very slightly decrease with increased amplitude, despite the main trend of increased variance of rate with increased rate.

Data from cat ganglion cells stimulated with sinusoidally modulated lights of various contrasts agree with the theory, although some individual cases show trends that may be indicative of nonlinearity in the relationship between variance of rate and rate.
Maturation of somatostatin immunoreactivity in the pigeon retina: Morphological characterization and quantitative analysis
Authors: Traina Giovanna , Fontanesi Gigliola , Bagnoli Paola
Published: June 2009

In addition to a modulatory function, somatostatin (SS) is likely to exert a morphogenetic and/or trophic role in the developing nervous system. In this study, a mouse monoclonal antibody directed to SS was used to investigate the posthatching development of SS-immunoreactivity (SS-ir) in the pigeon retina to provide a basis for a better understanding of the role of this peptide in retinal maturation. In the adult, SS-ir was observed in amacrine cells located in the inner nuclear layer (INL) of the entire retina. Two cell types were recognized according to their morphology. They showed a differential density distribution. Cell type indicated as “adult 1” (AD1) was characterized by pear-shaped cell bodies with single primary processes directed to the inner plexiform layer (IPL) and was mostly present in the red field. In contrast, cell type indicated as “adult 2” (AD2) was characterized by round-shaped somata with 1–3 primary processes and was highly represented in the fovea and the dorsal periphery. Posthatching maturation of the pigeon retina was characterized by drastic changes in the pattern of SS-ir. Over the first days posthatching, SS-ir was observed in sparsely distributed somata mostly located in the ganglion cell layer (GCL). This cell type indicated as “hatch” (H) was characterized by dense granular staining and became extremely rare at 7 days. Over the same period, growing SS-positive axons displaying enlarged growth cones were found in the optic tract (TrO). These observations suggest the possibility that ganglion cells transiently expressing SS are present at early stages of posthatching development. Of the two types of SS-containing cells observed in the adult, the first to be recognized morphologically was cell type AD1 which appeared at 2 days after hatching in the INL. These cells were virtually adult-like in morphology by 7 days. In contrast, cell type AD2 was not apparent until 7 days posthatching. The density (defined as number of cells/mm2 of retinal tissue) and the total number of SS-containing cells changed during posthatching maturation. In particular, the adult number of cell type AD1 was reached at about 10 days, while the number of cell type AD2 was reached at about 3 weeks posthatching. At this stage, both cell types also displayed their mature density distribution. The present findings suggest a temporal relationship between the maturation of SS-ir and developmental events which include the onset of light-driven activity and the maturation of retinal acuity. Our results also demonstrate significant differences in the pattern of SS-ir between the avian and the mammalian retina and suggest that SS-containing neurons represent important intraretinal association neurons in the retina of birds.
Columnar activity regulates astrocytic β-adrenergic receptor-like immunoreactivity in V1 of adult monkeys
Authors: Aoki Chiye , Lubin Mona , Fenstemaker Suzanne
Published: June 2009

Recent results indicate that astrocytic β-adrenergic receptors (βAR) participate in noradrenergic modulation of synaptic activity. In this study, we sought to examine whether neural activity can, in turn, regulate astrocytic βAR. To address this question, an antiserum that recognizes β-adrenergic receptors (βAR) specifically in astrocytes was used to assess the distribution of the receptors across ocular dominance columns in VI of two monocular and four visually intact adult monkeys. Cytochrome oxidase histochemistry (CO) was used to identify the position of the cortical laminae and of the ocular dominance columns receiving visual inputs from the intact and enucleated eyes. This stain revealed the expected pattern within V1 of monocular monkeys–i.e. darker and lighter bands of equal widths (ca. 500μm) spanning laminae 4–6, each associated with larger and smaller blobs, respectively, in lamina 2/3;. Alignment of CO sections with adjacent sections stained for astrocytic βAR by the immunoperoxidase method revealed intense βAR-like immunoreactivity (βAR-li) in the superficial laminae, a slightly weaker staining in the infragranular laminae and weakest staining in lamina 4C. Within lamina 4C., a prominent striped pattern was evident. The darker bands of the stripe closely matched widths and positions of the lighter CO columns associated with the enucleated eye. On the other hand, immunocytochemical staining for the astrocytic intermediate filament protein, GFAP, within V1 of monocular monkeys revealed no inter-columnar difference in the density of astrocytic cell bodies or processes. Nissl stain also revealed no overt inter-columnar differences in cell density. V1 of visually intact monkeys exhibited a similar laminar distribution pattern of βAR-li and of CO. Within lamina 4C., βAR-li was uniformly faint and CO staining was uniformly intense. This suggests that the striped pattern of βAR-li seen in lamina 4C of monocular monkeys results from elevation of the βAR-antigen within the inactive columns. The results indicate that astrocytic βAR density is regulated by local neural activity. The mechanisms regulating βAR density are likely to be independent of those regulating glial cell proliferation or GFAP synthesis. In vitro experimental results of others suggest that elevation of astrocytic βAR may be a mechanism compensating for chronic neural inactivity, since the coincident release of noradrenaline with visual stimulation would elevate neuropil excitability via the astrocytic mechanism of (1) decreasing the uptake of neuronally released L-glutamate; (2) increasing GABA uptake; and (3) stimulating glycogenolysis. Alternatively, the changes in βAR-li may reflect an up-regulation of the receptors within inactive columns due to reduced levels of noradrenaline release.
Neuronal organization and plasticity in adult monkey visual cortex: Immunoreactivity for microtubule-associated protein 2
Authors: Hendry Stewart H. C. , Bhandari Monica A.
Published: June 2009

Immunocytochemical staining for microtubule-associated protein 2 (MAP 2) was used to examine the morphology of neurons, the organization of neuronal groups, and the neurochemical plasticity of cells in adult monkey area 17. MAP 2-immunostained neurons are present through the depth of area 17 but are most intensely immunoreactive in layers IVB and VI. From layer IVB, separate groups of MAP 2-positive cells invade layers 1VA and IVCα. Clusters of cells protrude upward from superficial layer IVB and occupy the central core regions of the cytochrome oxidase (CO)-stained honeycomb in layer IVA, while large neurons typical of layer IVB are distributed in irregular clusters in the subjacent layer IVCa. The somata in the layer IVA honeycomb cores give off immunostained dendrites which remain largely within the core regions. Patches of MAP 2-positive neurons are also present in layers II and III, where they coincide with the CO-stained puffs.

Intravitreal injections of tetrodotoxin (TTX) into one eye of adult monkeys produce stripes of alternating light and dark MAP 2 immunostaining in layer IVC. Stripes of light immunostaining coincide with stripes of light CO staining, and correspond to reduced MAP 2 immunoreactivity within cortical neurons dominated by the TTX-injected eye. In layers II and III, the MAP 2 immunostaining of patches overlying the injected-eye columns is similarly reduced. No change occurs in the MAP 2 immunostaining of layer IVA.

These data suggest that the anatomical and physiological heterogeneity of layers IVA and IVCα arises from the periodic invasion of neurons characteristic of layer IVB, that the neurons in layer IVA have dendrites confined to thalamocortical-recipient or nonrecipient zones and that the expression of MAP 2 changes in adult cortical neurons following the loss of retinal input.
Monocular enucleation reduces immunoreactivity to the calcium-binding protein calbindin 28 kD in the Rhesus monkey lateral geniculate nucleus
Authors: Mize R. Ranney , Luo Qian , Tigges Margarete
Published: June 2009

The calcium-binding proteins calbindin (CaBP) and parvalbumin (PV) are important in regulating intracellular calcium in brain cells. PV immunoreactivity is reduced by enucleation in the lateral geniculate nucleus (LGN) and by enucleation and visual deprivation in the striate cortex of adult monkeys. The effects of enucleation and visual deprivation on CaBP immunoreactivity in the LGN are not known. We therefore have studied cells and neuropil in the LGN that are labeled by antibodies to CaBP in normal and visually deprived Rhesus monkeys to determine if there is an effect on this calcium-binding protein. One group of monkeys had one eye removed 2 weeks to 4.3 years before sacrifice. A second group had one eye occluded with opaque lenses from infancy without enucleation. A final group had one eye occluded long-term followed by short-term enucleation 2 weeks before sacrifice.

In normal monkeys, CaBP-immunoreactive neurons were found throughout the LGN. They were sparsely distributed within the six main laminae, and more densely distributed within layer S and the interlaminar zones (ILZ). The labeled ILZ neurons had a distinct morphology, with fusiform somata and elaborate dendritic trees that were confined primarily to the ILZ. Most CaBP-labeled neurons in the main layers had dendrites that radiated in all directions from the soma. ILZ and main layer cells labeled by CaBP thus probably represent two different cell types.

Monocular enucleation with or without occlusion produced a significant reduction in antibody labeling in the deafferented laminae. Field measures revealed an average 11.5% reduction in optical density in each deafferented lamina compared to its adjacent, nondeprived layer. The differences in field optical density between deprived and nondeprived layers were statistically significant. CaBP neurons were still visible, but the optical density of antibody labeling in these cells also was reduced. Occlusion without enucleation had no effect. Thus, deafferentation, but not light deprivation, reduces concentrations of CaBP in monkey LGN. This effect is different than that seen in striate cortex of adult monkeys, where visual deprivation as well as enucleation alters CaBP immunoreactivity.
A circadian clock in the Limulus brain transmits synchronous efferent signals to all eyes
Authors: Kass Leonard , Barlow Robert B.
Published: June 2009

A circadian clock in the brain of the horseshoe crab, Limulus polyphemus, has an important role in the function of the peripheral visual system. At night, the clock transmits neural activity to the lateral, ventral, and median eyes via efferent optic nerve fibers. The activity occurs in synchronous bursts (maximum rate of 2 bursts/s) with individual efferent fibers contributing a single spike in each burst. The circadian efferent activity originates in the protocerebrum. Lateral connections synchronize the efferent activity recorded from the two halves of the protocerebrum, suggesting the existence of bilateral circadian oscillators. Circadian efferent activity survives excision of the brain and isolation of the protocerebrum. We conclude that circadian clock and its complex neural circuitry are fundamental components of the Limulus visual system.
Brain-stem afferents upon retinal projecting isthmo-optic and ectopic neurons of the pigeon centrifugal visual system demonstrated by retrograde transneuronal transport of rhodamine β-isothiocyanate
Authors: Miceli Dom , Repérant Jacques , Bavikati Renuka , Rio Jean-Paul , Volle Michel
Published: June 2009

Brain-stem afferents to the n. isthmo-opticus (NIO) and ectopic neurons (EN) of the centrifugal visual system (CVS) were determined in the pigeon using the retrograde transneuronal transport of the fluorescent dye Rhodamine β-isothiocyanate (RITC) after its intraocular injection. In other experiments, either RITC was injected into various periocular tissues (controls) or the retrograde tracer Fluoro-gold (FG) was injected stereotaxically in the NIO. Following intraocular injections, the RITC retrograde labeling of cell bodies was observed contralaterally in the NIO and EN and transneuronally in layers 9/10 of the optic tectum, area ventralis-Tsai, zona peri-NIII, mesencephalic and pontine reticular formation (PRF), n. linearis caudalis-raphe, and bilaterally within a region referred to as zona peri-n.NVI (Zp-n.NVI) immediately underlying the abducens nerve nucleus. None of the above structures were labeled after RITC periocular injections. The FG labeling revealed that the tectal efferent neurons were mainly medium-sized, multipolar cells whose dendrites extended superficially to retino-recipient tectal layers 6 and 5. Quantitative measurements of the distribution of layers 9/10 RITC-labeled neurons indicated the highest densities to be localized within the ventral tectum corresponding to the representation of the dorsal retina and inferior visual field. We suggest that visual and nonvisual brain-stem afferents upon NIO and EN may play a role in the proposed mechanism of the avian CVS in attention, ground-feeding behavior, and modulation of retinal sensitivity.
Localization of the CD15 carbohydrate epitope in the vertebrate retina
Authors: Andressen Christian , Mai Jürgen K.
Published: June 2009

The distribution of the carbohydrate epitope CD 15, a putative cell adhesion molecule, was studied in adult vertebrate retinas by light-microscopic immunohistochemistry. Except for Old World primates, in which no immunoreactivity was detectable, all other species expressed the epitope on retinal interneurones. Subpopulations of stratified amacrine cells were found in all species with the exception of bats and marmoset monkeys, and bipolar cells were immunoreactive in frogs and all amniotic animals. Ganglion cells were labelled in urodelian, in all sauromorphian, as well as in some mammalian species. In some species, the distribution of immunoreactive neurones was correlated to areas of retinal specialization such as the visual streak in frogs and the dorsotemporal field in birds. In these parts of the retina with enhanced visual acuity, more CD 15 glycosylated bipolar cells were found than in other parts. Among mammals, labelled bipolar cells were found exclusively in species with cone-dominated retinas. This comparative study shows that CD 15 expression is consistently membrane associated in morphologically defined subsets of amacrine, bipolar, and ganglion cells throughout the vertebrate phylum. Its distribution pattern was found to depend more on the visual behavior of a given species (cone-dominated or rod-dominated retina) than on phylogenetic proximity between species.
Principal neuronal organization in the frog optic tectum revealed by a current source density analysis
Authors: Nakagawa Hideki , Miyazaki Hiromi , Matsumoto Nobuyoshi
Published: June 2009

In the frog optic tectum, the spatiotemporal pattern of neuronal activity evoked by electrical stimulation of the optic tract was examined by means of a current source density (CSD) analysis. The CSD depth profile was highly reproducible in different experiments. In all seven CSD profiles, three current sinks A, B, and D were observed in the retinorecipient layers. Four out of the seven profiles show additional two sinks C and E below the retinorecipient layers. Very small and short lasting sinks related to afferent fiber activities precede sinks A and B by about 1 ms, which could be accounted for by monosynaptic delay, in the corresponding depth region. The earliest prominent sink A at the bottom of the retinorecipient layers reflects only excitatory monosynaptic activities derived from R3 and/or R4 retinal ganglion cells. The second prominent sink B in the superficial retinorecipient layer is composed partly of excitatory monosynaptic activity from medium-sized myelinated optic fibers. It may involve excitatory monosynaptic activity from unmyelinated optic fibers and further polysynaptic activity. The fourth prominent sink D in the intermediate retinorecipient layer partially reflects excitatory monosynaptic activity derived from unmyelinated optic fibers. It may also involve further polysynaptic activity. In contrast with these three sinks, the third prominent sink C and fifth sink E exclusively reflect intratectal polysynaptic activity that has not been reported in any previous CSD studies in the frog optic tectum. These sinks almost overlap spatially in the tectal layer. We also measured the intratectal resistance changes and computed inhomogeneous CSD depth profiles to show that the results from homogeneous CSD computation assuming constant conductivity are valid for our present study. Finally, we compared the present results with previously reported CSD studies on the frog optic tectum and discuss consistencies and discrepancies among these experiments.
Projection status of calbindin- and parvalbumin-immunoreactive neurons in the superficial layers of the rat's superior colliculus
Authors: Lane Richard D. , Allan Dawn M. , Bennett-Clarke Carol A. , Howell David L. , Rhoades Robert W.
Published: June 2009

Immunocytochemistry and retrograde labeling were used to define the thalamic projections of calbindin- and parvalbumin-containing cells in superficial layers of the rat's superior colliculus (SC). Quantitative analysis revealed that 90.8 ± 2.2% (mean ± standard deviation) of the calbindin-immunoreactive neurons in the stratum griseum superficiale (SGS) projected to the dorsal lateral geniculate nucleus (LGNd) and that 91.3 ± 4.3% of calbindin-immunoreactive neurons in the stratum opticum (SO) projected to the lateral posterior nucleus (LP). In contrast, only 17.3 ± 2.5% of parvalbumin-immunoreactive neurons in the SGS were found to project to the LGNd and 16.5 ± 3.1% of the parvalbumin-immunoreactive SO cells were retrogradely labeled after LP injections. Few of the parvalbumin-immunoreactive neurons in either the SGS (7.2 ± 2.5%) or the SO (9.2 ± 2.5%) were GABA positive. The retrograde-labeling results suggest that parvalbumin-immunoreactive neurons in the rat's SO and SGS may either be primarily interneurons or have descending projections, while calbindin-containing cells are primarily thalamic projection neurons. These results are consistent with data from other rodents, but almost exactly the opposite of data that have been reported for the cat for these same populations of SC projection neurons. Such interspecies differences raise questions regarding the functional importance of expressing one calcium-binding protein versus another in a specific neuronal population.
The effect of a moving distractor on the initiation of smooth-pursuit eye movements
Authors: Ferrera Vincent P. , Lisberger Stephen G.
Published: June 2009

As a step toward understanding the mechanism by which targets are selected for smooth-pursuit eye movements, we examined the behavior of the pursuit system when monkeys were presented with two discrete moving visual targets. Two rhesus monkeys were trained to select a small moving target identified by its color in the presence of a moving distractor of another color. Smooth-pursuit eye movements were quantified in terms of the latency of the eye movement and the initial eye acceleration profile. We have previously shown that the latency of smooth pursuit, which is normally around 100 ms, can be extended to 150 ms or shortened to 85 ms depending on whether there is a distractor moving in the opposite or same direction, respectively, relative to the direction of the target. We have now measured this effect for a 360 deg range of distractor directions, and distractor speeds of 5–45 deg/s. We have also examined the effect of varying the spatial separation and temporal asynchrony between target and distractor. The results indicate that the effect of the distractor on the latency of pursuit depends on its direction of motion, and its spatial and temporal proximity to the target, but depends very little on the speed of the distractor. Furthermore, under the conditions of these experiments, the direction of the eye movement that is emitted in response to two competing moving stimuli is not a vectorial combination of the stimulus motions, but is solely determined by the direction of the target. The results are consistent with a competitive model for smooth-pursuit target selection and suggest that the competition takes place at a stage of the pursuit pathway that is between visual-motion processing and motor-response preparation.
Effects of adaptation level and hypoglycemia on function of the cat retina during hypoxemia
Authors: McRipley M. A. , Ahmed J. , Chen E. P. -C. , Linsenmeier R. A.
Published: June 2009

Acute hypoxemia (low PaO2) leads to changes in oxygen consumption and electrical responses of the outer retina of cats, but inner retinal ERG components and ganglion cell responses have been shown to be quite resistant to hypoxemia. The purpose of this study was to determine whether the resistance of the inner retina depends on (1) the stimulus conditions, specifically the degree of light adaptation; and (2) the ability of the photoreceptors to increase glycolysis during hypoxemia. To address these issues, recordings of single ganglion cell action potentials and of the b-wave and scotopic threshold response (STR) of the electroretinogram (ERG) were made from the eyes of anesthetized cats during hypoxemia alone and hypoxemia plus hypoglycemia. Ganglion cells appeared to be equally resistant to hypoxemia at high and low backgrounds (3.3 to 9.7 log equivalent quanta(555 nm)-deg-2-s-1), and the STR, recorded with dim stimuli during dark adaptation, when photoreceptor oxygen consumption is most susceptible to hypoxemia, was unchanged until PaO2 was below 30 mm Hg. The amplitude of the b-wave was similarly resistant to hypoxemia when the animal was normoglycemic. During hypoglycemia, however, both the b-wave and the STR became more sensitive to hypoxemia, beginning to change at PaO2s as high as 50 mm Hg when blood glucose was 40–50 mg/dl. It is argued that hypoglycemia limits or prevents the increased glycolytic ATP production that would ordinarily occur when the photoreceptor oxygen supply decreases, and that increased photoreceptor glycolysis is essential in the protection of the retina against mild hypoxemia.
Alpha ganglion cells of the rabbit retina lose antagonistic surround responses under dark adaptation
Authors: Muller Jay F. , Dacheux Ramon F.
Published: June 2009

Alpha ganglion cells from the midperiphery of the rabbit retina were recorded intracellularly under visual control, in a superfused everted eyecup, and labeled with HRP. Their physiology and large somata with broad dendritic arbors identified them as uniform populations of ON- and OFF-center alpha ganglion cells, which typically displayed transient/sustained light-evoked responses. When dark adapted, the light-evoked responses from both ON- and OFF-center alpha ganglion cells were more sustained than those generally seen under light-adapted conditions. During dark-adapted (scotopic) conditions, stimulation with dim full-field illumination and small spots, either positioned over the soma or displaced 450 μm from the soma, all elicited pure center responses. After light adaptation (photopic conditions), the displaced small spots that previously evoked center responses elicited antagonistic surround responses from both ON- and OFF-center cells. Thus, as originally described in cat retina (Barlow et al., 1957), the receptive-field organization of ganglion cells changed between dark and light adaptation, and an absence or presence of surround antagonism was indicative of scotopic versus photopic states.