bluuebunny/crossref_metadata_2025 huggingface dataset:
A role for the corpus callosum in visual area V4 of the macaque
Authors: Desimone Robert , Moran Jeffrey , Schein Stanley J. , Mishkin Mortimer
Published: June 2009

The classically defined receptive fields of V4 cells are confined almost entirely to the contralateral visual field. However, these receptive fields are often surrounded by large, silent suppressive regions, and stimulating the surrounds can cause a complete suppression of response to a simultaneously presented stimulus within the receptive field. We investigated whether the suppressive surrounds might extend across the midline into the ipsilateral visual field and, if so, whether the surrounds were dependent on the corpus callosum, which has a widespread distribution in V4. We found that the surrounds of more than half of the cells tested in the central visual field representation of V4 crossed into the ipsilateral visual field, with some extending up to at least 16 deg from the vertical meridian. Much of this suppression from the ipsilateral field was mediated by the corpus callosum, as section of the callosum dramatically reduced both the strength and extent of the surrounds. There remained, however, some residual suppression that was not further reduced by addition of an anterior commissure lesion. Because the residual ipsilateral suppression was similar in magnitude and extent to that found following section of the optic tract contralateral to the V4 recording, we concluded that it was retinal in origin. Using the same techniques employed in V4, we also mapped the ipsilateral extent of surrounds in the foveal representation of VI in an intact monkey. Results were very similar to those in V4 following commissural or contralateral tract sections. The findings suggest that V4 is a central site for long-range interactions both within and across the two visual hemifields. Taken with previous work, the results are consistent with the notion that the large suppressive surrounds of V4 neurons contribute to the neural mechanisms of color constancy and figure-ground separation.
A quantitative analysis of the effects of excitatory neurotoxins on retinal ganglion cells in the chick
Authors: Tung Ngoh Ngoh , Morgan Ian G. , Ehrlich David
Published: June 2009

The present study examines the differential effects of three excitotoxins, kainic acid (KA), N-methyl-D-aspartate (NMDA), and α-amino-2,3-amino-2,3-dihydro-5- methyl-3-oxo-4- isoxazolepropanoic acid (AMPA) on neurons within the genglion cell layer (GCL) of the chick retina. Two-day-old chicks were given a single, 5 μl, intravitreal injection of KA, NMDA, or AMPA at a range of doses. Following treatment with 40 nmol KA, there was a 21% loss of neurons in the GCL. At 200 nmol KA, the loss increased to 46%. Exposure to KA eliminated mainly small neurons of soma area 5–15μm2, and medium-sized ganglion cells of soma area 15–25μm2. Large ganglion cells (>25μ,2) remained unaffected. The vast majority of small cells were probably displaced amarcrine cells. At a does of 3000 nmol NMDA, no further loss of cells was evident. Exposure to 200 nmol AMPA resulted in a 30% loss of large and some medium-sized ganglion cells. In a further series of experiments, exposure to excitotoxin was followed by a retinal scratch, which eliminated retinal ganglion cells within the axotomized region. The results indicate that only a small proportion of displaced amacrine cells are destroyed by NMDA and AMPA, whereas virtually all displaced amarine cells are sensitive to KA. The findings of this study indicate the existence of subclasses of ganglion cells with specificity towards different types of excitatory amino acids (EAA).
Presumptive catecholaminergic ganglion cells in the pigeon retina
Authors: Keyser Kent T. , Britto Luiz R. G. , Woo Jong-Inn , Park Dong H. , Joh Tung H. , Karten Harvery J.
Published: June 2009

An antiserum directed against tyrosine hydroxylase (TH), the rate-limiting enzyme in the synthesis of dopamine, was used to study the pigeon retina. Labeled cells were observed in both the inner nuclear layer (INL) and ganglion cell layer (GCL). Two populations of TH-immunoreactive neurons were observed in the INL. Some of these cells were 7−10 μ in diameter and gave rise to processes that arborized in three Layers of the inner plexiform layer (IPL). These cells appeared similar to the dopaminergic amacrine cells described previously (Marc, 1988). Other labeled cells in the INL were 12−20 μ in diameter and were recognizable as a previously described subpopulation of TH-immunoreactive displaced ganglion cells (Britto et al., 1988).

A population of labeled cells was observed in the GCL. Counts of these cells in two retinae revealed 5000 and 7000 cells, respectively. They ranged in size from 8−15 μ in diameter in the central retina and from 8−20 m in diameter in the peripheral retina. The density of labeled cells was highest in the central retina and red field and lowest in the retinal periphery. The difference in cell size and cell density as a function of eccentricity is characteristic of the total population of ganglion cells in the avian retina (Ehrlich, 1981; Hayes, 1982). Some of the TH-positive cells in the GCL could be classified as ganglion cells for two reasons: (1) The axons of many of the TH-positive cells in the GCL were TH-immunoreactive as well and could be followed to the optic nerve head. (2) The injection of rhodamine-labeled microspheres into the nucleus geniculatus lateralis, pars ventralis (GLv), resulted in the retrograde labeling of many of the TH-positive cells in the contralateral retina.
Multiple subtypes of glycine-immunoreactive neurons in the goldfish retina: Single- and double-label studies
Authors: Yazulla Stephen , Studholme Keith M.
Published: June 2009

The glycinergic system in goldfish retina was studied by immunocytochemical localization of glycine antiserum at the light-microscopical level. Numerous amacrine cells, a type of interplexiform cell, interstitial cell, and displaced amacrine cell were glycine-immunoreactive (IR). Amacrine cells, accounting for 97% of the glycine-IR neurons, were of four types based solely on their level of dendritic stratification: stratified amacrine cells of the first, third, and fifth sublayers and bistratified amacrine cells of the first and fifth sublayers. Double-labeling experiments were carried out to determine possible co-localization of glycine-IR with GABA-IR, serotonin-IR, substance P-IR and somatostatin-IR. No evidence for co-localization of glycine-IR with these other transmitter substances was found, despite reports of co-localization of these substances in retinas of other species. Glycinergic neurons in goldfish retina appear to consist of a heterogeneous population of at least seven morphologically distinct subtypes that are also neurochemically distinct in regard to GABA, serotonin, substance P, and somatostatin. Since dendritic stratification in the inner plexiform layer is correlated with ON-, OFF-response types, we suggest that the subtypes of glycine-IR amacrine cells play different roles in the encoding of visual information.
Chemically induced retinal degeneration in therdgB(retinal degeneration B) mutant ofDrosophila
Authors: Rubinstein Chaim T. , Bar-Nachum Shoshana , Selinger Zvi , Minke Baruch
Published: June 2009

Chemicals which affect different steps of the phototransduction cascade were used to identify the site of action of therdgBgene product ofDrosophila. In therdgBmutant, the photoreceptor cells degenerate after several days of exposure to light, whereas raising the flies in the dark largely prevents the degeneration. In therdgBKS222mutant, which was used in the present studies, the light-induced degeneration is characterized by (1) selective degeneration of the peripheral but not the central photoreceptor cells; (2) random distribution of degenerated cells among ommatidia; and (3) the degeneration is specific to therdgBbut not the wild-type photoreceptor cells. In the present study, we show that application of specific chemical agents to the eyes ofrdgBKS222flies in the dark mimics the effects of light and causes retinal degeneration indistinguishable from light. The agents used in these studies are the metabolically stable GTP analogs GTPγS and Gpp(NH)p as well as fluoride ions, which are known to activate the transducing guanine nucleotide binding protein (G-protein of fly photoreceptors). It is unlikely that the chemically induced retinal degeneration is mediated by effects on energy metabolism, since application of the metabolic inhibitors CN-and 2-deoxy-D-glucose did not increase the extent of retinal degeneration over that observed in control flies treated with Ringer solution. The GDP analog GDPβS, which inhibits G-protein activity, greatly reduced the extent of retinal degeneration in the dark, over that observed in control flies treated with Ringer solution. These results suggest that activation of the G-protein precedes the step in the transduction cascade that leads to retinal degeneration and provides a powerful tool to investigate the molecular mechanism of light-induced degeneration in therdgBmutant.
A GAP-43-like protein in cat visual cortex
Authors: McIntosh Helen , Parkinson David , Meiri Karina , Daw Nigel , Willard Mark
Published: June 2009

We have purified a protein that changes in relative concentration during the development of the kitten visual cortex. It resembles GAP-43 (a neuronal protein that is expressed at elevated levels during periods of development and regenerative axon growth) in the following respects: (1) it is an acidic protein (pI=4.7) whose electrophoretic mobility on SDS-PAGE is similar to, but lower than rat GAP-43, suggesting that the cat protein is larger; (2) its electrophoretic mobility varies with the acrylamide concentration in a manner that is characteristic of GAP-43; (3) its concentration in kitten forebrain is elevated during early postnatal development; (4) the sequence of ten consecutive amino acids from a chemically generated fragment matches the expected sequence from GAP-43; and (5) its amino-acid content also matches GAP-43. We conclude that our purified protein is cat GAP-43. Immunoblots with an antibody prepared against rat GAP-43 suggested that the concentration of GAP-43 in the visual cortex declines with age.
Adaptation in single units in visual cortex: The tuning of aftereffects in the spatial domain
Authors: Saul A. B. , Cynader M. S.
Published: June 2009

Cat striate cortical neurons were investigated using a new method of studying adaptation aftereffects. Stimuli were sinusoidal gratings of variable contrast, spatial frequency, and drift direction and rate. A series of alternating adapting and test trials was presented while recording from single units. Control trials were completely integrated with the adapted trials in these experiments.

Every cortical cell tested showed selective adaptation aftereffects. Adapting at suprathreshold contrasts invariably reduced contrast sensitivity. Significant aftereffects could be observed even when adapting at low contrasts.

The spatial-frequency tuning of aftereffects varied from cell to cell. Adapting at a given spatial frequency generally resulted in a broad response reduction at test frequencies above and below the adapting frequency. Many cells lost responses predominantly at frequencies lower than the adapting frequency.

The tuning of aftereffects varied with the adapting frequency. In particular, the strongest aftereffects occurred near the adapting frequency. Adapting at frequencies just above the optimum for a cell often altered the spatial-frequency tuning by shifting the peak toward lower frequencies. The fact that the tuning of aftereffects did not simply match the tuning of the cell, but depended on the adapting stimulus, implies that extrinsic mechanisms are involved in adaptation effects.
Adaptation in single units in visual cortex: The tuning of aftereffects in the temporal domain
Authors: Saul A. B. , Cynader M. S.
Published: June 2009

Adaptation-induced changes in the temporal-frequency tuning and direction selectivity of cat visual cortical cells were studied. Aftereffects were induced largely independent of direction. Adapting in either direction reduced responses in both directions. Aftereffects in the direction opposite that adapted were only slightly weaker than were aftereffects in the adapted direction. No cell showed any enhancement of responses to drifting test stimuli after adapting with moving gratings. Adapting in a cell's null direction usually had no effect. Dramatic differences between the adaptation characteristics of moving and stationary stimuli were observed, however.

Furthermore, aftereffects were temporal frequency specific. Temporal frequency-specific aftereffects were found in both directions: adapting in one direction induced frequency-specific effects in both directions. This bidirectionality of frequency-specific aftereffects applied to the spatial domain as well. Often, aftereffects in the direction opposite that adapted were more narrowly tuned.

In general, adaptation could shift a cell's preferred temporal frequency. Aftereffects were most prominent at high temporal frequencies when testing in the adapted direction. Aftereffects seemed to be more closely linked to temporal frequency than to velocity matching.

These results constrain models of cortical connectivity. In particular, we argue against schemes by which direction selectivity is generated by inhibiting a cell specifically when stimulated in the nonpreferred direction. Instead, we argue that cells receive bidirectional spatially and temporally tuned inputs, which could combine in spatiotemporal quadrature to produce direction selectivity.
Mature, growing ganglion cells acquire new synapses in the retina of the goldfish
Authors: Hitchcock Peter F.
Published: June 2009

The goldfish retina grows throughout the animal’s life, primarily by a balloon-like expansion. With this expansion, dendritic arbors of ganglion cells show scaled growth; arbors increase in size from small to large with no change in their architecture (Hitchcock & Easter, 1986; Bloomfield & Hitchcock, 1991). The study reported here showed that ganglion cell arbors acquire new synapses with this growth. Arbors from a single type of ganglion cell in retinas of small, young and large, old fish were intracellularly filled with horseradish peroxidase, examined electron microscopically, and the synapses contacting them counted and compared (small arborsvs. large arbors). The small and large arbors had similar numbers and orders of dendritic branches (i.e. similar architectures), but the large arbors were significantly larger than the small ones. The increase in arbor size was correlated with a 2.7x and 1.9x increase in the number of ribbon and conventional synaptic contacts, respectively. The addition of new synapses is proposed as a mechanism by which the signaling properties of the enlarging ganglion cells can remain constant.
Gap-junctional properties of electrically coupled skate horizontal cells in culture
Authors: Qian Haohua , Malchow Robert Paul , Ripps Harris
Published: June 2009

Whole-cell voltage-clamp recordings were used to examine the unusual pharmacological properties of the electrical coupling between rod-driven horizontal cells in skate retina as revealed previously by receptive-field measurements (Qian & Ripps, 1992). The junctional resistance was measured in electrically coupled cell pairs that had been enzymatically isolated and maintained in culture; the typical value was about 19.92 MΩ(n = 45), more than an order of magnitude lower than the nonjunctional membrane resistance. These data and the intercellular spread of the fluorescent dye Lucifer Yellow provide a good indication that skate horizontal cells are well coupled. The junctional conductance between cells was not modulated by the neurotransmitters dopamine (200 μM) or GABA (1 mM), nor was it affected by the membrane-permeable analogues of cAMP or cGMP, or the adenylate cyclase activator, forskolin. Although resistant to agents that have been reported to alter horizontal-cell coupling in cone-driven horizontal cells, the junctional conductance between paired horizontal cells of skate was greatly reduced by the application of 20 mM acetate, which is known to effectively reduce intracellular pH. Together with the results obtained in situ on the receptive-field properties of skate horizontal cells, these findings indicate that the gap-junctional properties of rod-driven horizontal cells of the skate are fundamentally different from those of cone-driven horizontal cells in other species. This raises the possibility that there is more than one class of electrical synapse on vertebrate horizontal cells.
The cone photoreceptor mosaic of the green sunfish,Lepomis cyanellus
Authors: Cameron David A. , Easter Stephen S.
Published: June 2009

Recent empirical and theoretical evidence has implicated the geometrical birefringence of the double cones of the green sunfish (Lepomis cyanellus) as the biophysical basis of this vertebrate’s sensitivity to polarized light. Because of the intimate link between the organization of the cone-photoreceptor mosaic and the psychophysical details of polarization sensitivity, we have examined the structural features of the green sunfish cone-photoreceptor mosaic, in particular the orientation of the elliptical cross sections of the double cones. Our primary observations are that (1) the arrangement of the cone-photoreceptor mosaic is constant across the retina (with two regional exceptions), with double cones arranged in a rhombic mosaic and aligned roughly ±45 deg to the nearest retinal margin; (2) the double-cone/single-cone ratio is everywhere the same; (3) cone density is inhomogeneous across the retina, with the highest densities in the temporal hemiretina. These results are discussed as they relate to the animal’s retinal growth and visual mechanisms, particularly the sensitivity to polarized light.
Development of dendritic trees of rabbit retinal alpha ganglion cells: Relation to differential retinal growth
Authors: Deich C. , Seifert B. , Peichl L. , Reichenbach A.
Published: June 2009

To provide a quantitative description of the postnatal development of dendritic trees in alpha ganglion cells of the rabbit retina, these cells were stained either by intracellular injection of Lucifer yellow or by application of the lipophilic dye Oil. This was done at three developmental stages: postnatal day (P) 8/9, P 16/17, and in adults. For different retinal locations we quantified the alpha cell dendritic field area, the number of dendritic branch points, and the average dendritic length between branch points. According to the alpha cell location, the data were collected in three groups representing the retinal center, midperiphery, and far periphery, respectively. The data were then correlated with the postnatal retinal expansion which is known to differ among the above topographic regions of the retinae (Reichenbach et al., 1993). Our results show that the growth of alpha ganglion cell dendrites is not proportional to, but significantly exceeds, that of the local retinal tissue. Between P 8/9 and adulthood, the area of central alpha cells increases almost six-fold from 26,000 to 144,000 μm2(retinal expansion: 2.2-fold), and that of peripheral cells more than 15-fold from 35,000 to 556,000 μm2(retinal expansion: four-fold). During this period, the coverage factor of alpha cell dendritic fields increases about three-fold, and reaches adult levels of about 3 (retinal center) and 2.2 (periphery), respectively. The number of dendritic branch points remains nearly constant, and the distance between them increases by a factor close to the square root of the factor by which the dendritic field area grows. Thus, it appears that, from the second postnatal week on, dendritic trees of rabbit alpha ganglion cells increase by intense “interstitial growth,” rather than by outgrowth of (new) dendritic branches. This growth pattern is different from that of some other rabbit retinal ganglion cell types, and of alpha ganglion cells of the cat retina, whose dendritic trees expand at a rate equal to or less than that of the surrounding retinal tissue. The consequences for synaptic contacts with bipolar and amacrine cells are discussed; they suggest a high degree of synaptic plasticity during normal postnatal retinal growth.
Mechanism of anomalous retinal correspondence: Maintenance of binocularity with alteration of receptive-field position in the lateral suprasylvian (LS) visual area of strabismic cats
Authors: Grant Simon , Berman Nancy E. J.
Published: June 2009

We have examined the effects of rearing kittens with a unilateral convergent strabismus, induced surgically at 3 weeks of age, on the binocularity (ocular dominance) and receptive-field position of neurons in the motion-sensitive lateral suprasylvian (LS) area of cat extrastriate cortex. Data were compared to those obtained from area 17 in the same animals, and from the two areas of cortex in normal adult cats. Interocular alignment of the operated cats was assessed in alert adults using corneal reflex photography and during recording from the positions of retinal landmarks under paralysis. The strabismus magnitude in each operated cat was calculated by comparison with equivalent data from the normal animals.

Strabismus always caused a major loss of binocularity in area 17. The remaining binocular neurons had receptive-field (RF) pairs arising from positions of normal correspondence in the two retinae and would thus have been responsive to different regions of visual space through the misaligned eyes in the alert animal. In area LS, the effects were dependent on the strabismus magnitude. In the group of four cats with pronounced strabismus (18–30 deg crossed), a loss of binocularity occurred in area LS equivalent in severity to that in area 17. The majority of the remaining binocular LS neurons possessed RF pairs in normal retinal correspondence and would thus, in the alert animal, have received spatially disparate visual input through the two eyes. This also occurred in three other cats with more moderate strabismus (11–15 deg crossed), although only a small breakdown in the binocularity of area LS was apparent. The group of cats with mild strabismus (≤10 deg crossed) had normal proportions of binocular neurons in area LS. In three of these cats, the maintenance of binocularity was accompanied by shifts in RF position, with visual inputs arising from anomalous retinal locations. These shifts compensated, in part, for the strabismus angle present in each cat, so that most of the binocular LS neurons would have received inputs from regions of visual correspondence through the misaligned eyes when the animal was alert.

Similar mechanisms could afford a basis for the binocular visual compensations that occur in humans with small-angle strabismus of early onset. If so, anomalous retinal correspondence in such individuals would have as a locus areas of extrastriate cortex with a role in motion perception, and would involve alterations to the neural substrate underlying normal binocular vision.
Suppression of cone-driven responses by rods in the isolated frog retina
Authors: Dong Cun-Jian , Qian Hao-Hua , McReynolds John S. , Yang Xiong-Li , Liu Yu-Min
Published: June 2009

The sensitivity of rod- and cone-driven responses was studied in the isolated frog retina during the period of rapid dark adaptation following a conditioning flash which bleached a negligible amount of visual pigment. Following a conditioning flash, cone-driven b-wave responses were first enhanced and then depressed. The time courses of the enhancement and subsequent depression of cone-drive responses varies greatly with the intensity and wavelength of the conditioning flash, but were identical when the conditioning' flashes were matched for equal excitation of 502 nm rods. These changes in cone-driven response sensitivity were correlated with the desensitization and recovery of rods following the conditioning flash. When signal transmission from rods to second-order cells was interrupted by the addition of L-glutamate, the conditioning flash did not produce the above-described enhancement and subsequent depression of long-wavelength receptor potential responses. The suppression of cone-driven response therefore appears to be due to a synaptically mediated influence from 502 nm rods which is maximal when the rods are in the dark-adapted state, with little or no contribution from 433 nm rods, and no involvement of the pigment epithelium.
Intensity, color, and pattern discrimination deficits after lesions of the core and belt regions of the ectostriatum
Authors: Bessette Brenda B. , Hodos William
Published: June 2009

Pigeons were trained to discriminate visual stimuli that differed in intensity, color, or pattern, after which lesions were made in the ectostriatum, either the core region (EC), the belt region (EB), or both (EC + EB). Control lesions were made in the lateral neostriatum. After surgery, the birds were again trained to discriminate the stimuli. On the basis of a quantitative analysis of the lesion reconstructions, each pigeon was assigned to one of five groups: EC, EB, moderate (EC + EB), slight (EC + EB), or control. Postoperative savings scores, based on the number of preoperative and postoperative sessions required to discriminate the stimuli, were calculated. An analysis of variance indicated a significant effect of lesion location on the extent of postoperative savings or loss. Only the moderate (EC + EB) group was significantly different from the neostriatum controls. A multiple regression analysis of performance on the individual discrimination tasks indicated that the extent of damage to EC predicted the initial performance deficit on the intensity and one of the two pattern discrimination tasks (vertical versus horizontal bar). The color discrimination deficit, which was modest in extent and of short duration, was predicted only by the damage to (EC + EB) that was at least moderate in extent (20–40% of the volume of (EC + EB)).
Neuropeptide Y-Containing Neurons are Situated Predominantly Outside Cytochrome Oxidase Puffs in Macaque Visual Cortex
Authors: Kuljis Rodrigo O. , Rakic Pasko
Published: June 2009

Layers II/III of the primary visual cortex contain a regular pattern of histochemically detectable cytochrome oxidase (CO)-rich “puffs,” which differ from the interpuff regions in their thalamo-cortical and cortico-cortical connectivity, receptive-field properties, and the density of inhibitory GABA-containing synaptic terminals. We used an immunocytochemical method, in combination with cytochrome oxidase histochemistry, to analyze the spatial relationship between neurons that contain neuropeptide Y (NPY) and the CO puffs. Of a total of 606 neurons, only 2.6% of the NPY-containing cells are located in the puffs, whereas the rest are situated in the interpuffs, or at the interface between puffs and interpuffs. The number of NPY-containing neurons in the puffs is substantially less than that expected in an equal volume of the interpuffs (X2 = 13.86; df = 1; P < 0.001).

These observations indicate that columns containing the puffs may differ also from those in the interpuff regions in that they contain a unique array of chemically and morphologically distinct local circuit neurons.
Selective Labeling of Visual Corpus Callosum Connections with Aspartate in Cat and Rat?
Authors: Elberger Andrea J.
Published: June 2009

Tritiated neurotransmitter candidates were unilaterally injected in visual cortical regions with abundant corpus callosum connections. D-aspartate (Asp) or gamma-aminobutyric acid (GABA) was injected along the area 17/18 border in cat, and the area 17/18a and 17/18b borders in rat. Retrograde Asp label was found contralaterally in supragranular and infragranular laminae in areas 17, 18, 19, PMLS, and PLLS in cat, and in areas 29, 18b, 17, and 18a in rat. No contralateral GABA label was found in cat or rat. Thus, the cat and rat corpus callosum may use Asp or a related substance as a neurotransmitter.
Light-regulated proteins inLimulusventral photoreceptor cells
Authors: Edwards Samuel C. , Wishart Anne C. , Wiebe Eric M. , Battelle Barbara-Anne
Published: June 2009

The protein intermediates of the photoresponse and the modulation of this response in invertebrate photoreceptors are largely unknown. As a first step toward identifying these proteins, we have examined light-stimulated changes in protein phosphorylation in preparations ofLimulusphotoreceptors. Here we show that light modulates the level of phosphorylation of three proteins associated withLimulusventral photoreceptors: the upper band of a 46-kD protein doublet (46A) and a 122-kD protein, which become more heavily phosphorylated in response to light, and the lower component of the 46-kD doublet (46B), which is phosphorylated in dark-adapted cells, but not in cells maintained in the light. In dark-adapted preparations, 46A is phosphorylated within 30 s after a flash of light and dephosphorylates over a period of many minutes. It is also a major substrate for calcium/calmodulin-dependent protein kinase (Wiebe et al., 1989); therefore, we speculate that 46A is involved in some aspect of dark adaptation. Interestingly, the level of phosphorylation of 46A is the same when measured from preparations maintained in complete darkness or ambient light for at least 1.5 h. The 122-kD phosphoprotein is the same protein which becomes phosphorylated in response to efferent innervation toLimuluseyes (Edwards et al., 1988) and the efferent neurotransmitter, octopamine (Edwards and Battelle, 1987). It may be involved in the increase in retinal sensitivity and the enhanced response of photoreceptors to light that is initiated by efferent innervation. Its role in light-stimulated processes is not clear. The level of phosphorylation of 46B may be most relevant to the long-term state of adaptation of the photoreceptor cell to light and dark.
Nucleus isthmi in goldfish:In vitrorecordings and fiber connections revealed by HRP injections
Authors: King W. Michael , Schmidt John T.
Published: June 2009

Recordings of field potentials in nucleus isthmi (NI) were obtained in anin vitropreparation of goldfish brain using a lateral approach. Horseradish peroxidase (HRP) was injected from recording electrodes to verify recordings within the nucleus and to label axonal pathways and cell bodies. Activity in NI was repetitive and could be elicited by stimulation of the optic nerve, tectum, pretectum, or tectobulbar tract. Spontaneous activity was present in some preparations and consisted of bursts with intervening silent periods. Anatomical and electrophysiological evidence indicated that the primary isthmotectal pathway is composed of fine fibers that exit NI rostrally and pass through pretectum to enter tectum rostrally. An afferent pathway consisting of both fine- and large-diameter fibers entered NI ventromedially; the large diameter axons have been previously reported in percomorph fishes, but were not thought to be present in cyprinids such as goldfish. The large diameter axons arise from labeled cell bodies in the region of the lateral thalamic nucleus. No labeled cell bodies were seen in ipsilateral nucleus pretectalis superficialis, pars magnocellularis, where they are seen in percomorphs. The fine axons, which have not been reported in percomorph fishes, were shown to arise from tectal bipolar (type VI) neurons. As in percomorphs, tectal type XIV neurons were also labeled. This and corroborating recordings from nucleus isthmi constitute the first demonstration of a tectoisthmic projection in a cyprinid fish.
Neuromodulation of pigment movement in the RPE of normal and 6-OHDA-lesioned goldfish retinas
Authors: Ball Alexander K. , Baldridge William H. , Fernback Timothy C.
Published: June 2009

The role of dopamine as the endogenous signal-initiating light-dependent changes in the distribution of pigment granules in goldfish retinal pigment epithelium was investigated. In normal retinas, light adaptation resulted in the dispersion of pigment granules. This effect of light was mimicked by the intraocular injection of dopamine or serotonin, which is thought to increase endogenous dopamine release, into dark-adapted eyes. The effect of light, dopamine, or serotonin on dark-adapted retinas was blocked by the dopamine receptor antagonists haloperidol and sulpiride. However, lesioning the endogenous source of retinal dopamine, by prior intraocular injection of 6-hydroxydopamine (6-OHDA), did not block the dispersion of pigment granules in light-adapted retinas. No significant differences in pigment dispersion were noted between unlesioned and lesioned light- or dark-adapted retinas. However, the effect of light on pigment dispersion was no longer blocked by haloperidol or sulpiride in 6-OHDA lesioned animals. Dopamine and serotonin mimicked the effect of light when injected into lesioned dark-adapted eyes, but their effects were also not blocked by haloperidol or sulpiride. These results suggest that dopamine, acting on D2receptors, is sufficient to induce pigment migration in unlesioned animals. In 6-OHDA-lesioned animals, however, pigment migration is mediated by a receptor mechanism other than D2.
Localization of GABAAreceptors in the rat retina
Authors: Greferath Ursula , Müller Frank , Wässle Heinz , Shivers Brenda , Seeburg Peter
Published: June 2009

Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the mammalian retina. The present paper describes the localization of GABAAreceptors in the rat retina as revealed byin situhybridization and immunocytochemistry.

In situhybridization with probes against variousasubunits revealed a marked differential expression pattern. The αl subunit gene is expressed mainly in the bipolar and horizontal cell layer, the α2 gene in the amacrine and ganglion cell layer, and the α4 gene in a subpopulation of amacrine cells. β subunit mRNA is present diffusely throughout the entire inner nuclear layer and in the ganglion cell layer.

The monoclonal antibody bd 17 (against β2/β3 subunits) stained subpopulations of GABAergic and glycinergic amacrine cells as well as some ganglion cells and bipolar cells. Immunoreactivity was not restricted to synaptic input sites. In the outer plexiform layer bipolar cell dendrites were immunoreactive; in the inner plexiform layer mainly amacrine and ganglion cell processes were labeled, and bipolar cell axons appeared unstained. The results demonstrate a strong heterogeneity of GABAAreceptors in the retina.
Mechanisms of early visual processing in the medulla of the locust optic lobe: How self-inhibition, spatial-pooling, and signal rectification contribute to the properties of transient cells
Authors: Osorio D.
Published: June 2009

In the arthropod medulla, which is the second ganglion on the afferent visual pathway, a column of about 40 cells represents each point in space (i.e. compound eye facet). Some stages of visual processing underlying the responses of one class of cells in the locust medulla have been identified. Thesetransient cellsgive very similar responses to intensity increments and decrements, and also to pulses and steps; there is no spontaneous activity and a stimulus causes one or two spikes to fire at fixed latencies. Movement, however, produces a prolonged spike discharge by successive excitation of subunits within the receptive field.

One of the main features of the transient cells' responses is a self-inhibition which attenuates responses to successive stimuli at one point. This inhibition is restricted to the outputs of single receptor (rhabdom), it decays after about 100 ms, and is polarity sensitive so that stimuli of one polarity (e.g. dimming) do not inhibit responses to stimuli of the opposite polarity (e.g. brightening). The inhibition effectively alters the contrast threshold of the cells, because after adaptation with stimuli of one contrast, a modest (<20%) increase in contrast is sufficient to elicit an unadapted response. Transient cells are not directionally selective and there are no local spatio-temporal interactions of the kind necessary for directional selectivity. But, by analogy with the directional veto in directionally selective cells in the rabbit retina (Barlow & Levick, 1965), self-inhibition is suggested as a mechanism of non-directional motion detection. After the inhibition, there is some spatial pooling of signals which is followed by rectification. The transient cells' spiking outputs could abstract a refined subset of visual information which may encode the presence, but not the direction, amplitude, or polarity of moving object borders.
Antibodies to human leucocyte antigens indicate subpopulations of microglia in human retina
Authors: Penfold P.L. , Madigan M.C. , Provis J.M.
Published: June 2009

Monoclonal antibodies to human leucocyte antigens, including anti-CD45 and anti-CD68, have been used to describe microglia in flatmounts of normal adult human retina for the first time. Anti-CD45 (the leucocyte common antigen) intensely labeled large numbers of cells in a regular distribution across the retina; anti-CD68 and anti-macrophage antibodies labeled fewer cells with distinctive morphologies, suggesting the presence of subpopulations of microglia in the human retina expressing leucocyte antigens.
Requirement of N-linked glycosylation site inDrosophilarhodopsin
Authors: O'Tousa J. E.
Published: June 2009

In vitromutagenesis and germline transformation were used to create aDrosophilamutant, ΔAsn20lacking the N-linked glycosylation site near the amino terminus of the major rhodopsin (Asn20-Gly-Ser changed to Ile-Gly-Ser). Low opsin protein levels are detected in ΔAsn20photoreceptors. Electroretinogram responses of mutant flies show that the residual rhodopsin found in this mutant is capable of initiating phototransduction. The organization of rhabdomeres, the photoreceptor organelle containing nearly all of the rhodopsin, is aberrant in the ΔAsn20mutant and undergoes age-dependent deterioration. These results establish that an N-linked glycosylation site, and likely glycosylation itself, plays a critical role in the maturation ofDrosophilarhodopsin.
Spatial zones of binocular rivalry in central and peripheral vision
Authors: Blake Randolph , O'Shea Robert P. , Mueller T. J.
Published: June 2009

This paper presents results from psychophysical experiments on human binocular rivalry in central and peripheral vision. Results show that the incidence of periods of exclusive visibility of a given eye's rival target increased with decreasing target size, and for a given sized target exclusive visibility increased with retinal eccentricity. Control measures confirmed that these results were not attributable solely to reduced peripheral acuity, to Troxler's effect, or to spatial frequency. We computed the minimum-sized stimulus that would lead to a criterion level of exclusive visibility of one or the other eye; this we term the spatial zone of binocular rivalry. The change in estimated size of spatial zones of rivalry with eccentricity compares favorably with estimates of human cortical magnification. We propose a model that assumes concentrically organized zones of rivalry. These zones do not function independently, but instead exhibit a high degree of mutual excitatory cooperativity. The model has multiple solutions for the foveal zone size, but the best fits predict a diameter of 5.3 or 7.3 min of visual angle; these values dovetail nicely with our empirical estimates of the foveal zone size.
Synaptic contacts of a two-cone flat bipolar cell in a primate retina
Authors: Hopkins J. M. , Boycott B. B.
Published: June 2009

The Golgi-stained dendrites of a two-cone bipolar cell of a vervet monkey were serially sectioned for electron microscopy and shown to make basal synapses with two neighboring cones. The synapses were all on the cone pedicle membrane adjacent to the bipolar processes invaginating to form the triads. This is the characteristic position for flat midget bipolar cells. The numbers of triads in nine adjacent cone pedicles were not significantly different from those in the cones contacted by the bipolar. Based on this measure the two-cone bipolar does not contact a special population of cones.

The advantages and disadvantages of using vertical or horizontal sections for the determination by electron microscopy of the connectivity of the dendrites of Golgi-stained flat bipolar cells are discussed.
Wavelength-dependent temporal properties of retinal horizontal cells in turtles
Authors: Dvorak C.A. , Granda A.M.
Published: June 2009

Electrical reponses of luminosity horizontal cells (L cells) to monochromatic stimuli were analyzed by intracellular recordings in the retinas of the freshwater turtle (Pseudemys scripta elegans) and of the sea turtle (Chelonia mydas mydas). Light intensity, duration, and wavelength were varied to assess temporal effects. For a given intensity of monochromatic light, response amplitude increased with stimulus duration until maximum amplitude occurred at a specific duration. This suprathreshold metric of temporal integration is calledhere summation time, and it is wavelength-dependent.

L cells always had some level of red-sensitive cone input, although in some cells inputs from green- and blue-sensitive cones were also observed. For these latter cells, summation times were shorter for 640-nm than for 540-nm or 450-nm lights. These results were most evident in cells that received dominant inputs from blue- or green-sensitive cones.

Responses of some other L cells were almost completely dominated by inputs from red-sensitive cones. Summation times of these cells were not wavelength-dependent. But when these inputs also included green-sensitive cones, shorter summation times were obtained to 640-nm light than to 540-nm light, even though dominant inputs were still from red-sensitive cones. These results, obtained from both retinal and 3,4-dehydroretinal photopigment systems, are consistent with reported observations inPseudemys scripta elegansthat show linear responses of red-sensitive cones to have shorterintegration times and times-to-peakthan green-sensitive cones.

Responses from horizontal cells dominated by blue-sensitive cone inputs were the most sensitive of all; they also had the longest summation times. These results support the hypothesis that a gain in sensitivity occurs from the integration of absorbed photons over longer periods of time.

These intracellular responses are of particular importance because behavioral critical durations in turtle, as defined by Bloch&'s law, are similarly wavelength-dependent.
Phototransduction and adaptation in rods, single cones, and twin cones of the striped bass retina: A comparative study
Authors: Miller James L. , Korenbrot Juan I.
Published: June 2009

We investigated the attributes of transduction and light-adaptation in rods, single cones, and twin cones isolated from the retina of striped bass (Morone saxatilis). Outer-segment membrane currents were measured with suction electrodes under voltage clamp provided by tight-seal electrodes applied to the cell’s inner segment. Brief flashes of light transiently reduced the outer-segment current with kinetics and sensitivity characteristic of each receptor type. In all cells, the responses to dim lights increased linearly with light intensity. The amplitude-intensity relation for rods and single cones were well described by an exponential saturation function, while for twin cones it was best described by a Michaelis-Menten function. At the wavelength of maximum absorbance, the average intensity necessary to half-saturate the peak photocurrent in dark-adapted rods was 28 photons/μm2and in single cones it was 238 photons/μm2. Among twin cones, the common type (88% of all twins recorded) half-saturated at an average of 1454 photons/μm2, while the fast type reached half-saturation at an average of 9402 photons/μm2. The action spectrum of the photocurrent in the three receptor types was well fit by a nomogram that describes the absorption spectrum of a vitamin A2-based photopigment. The wavelength of maximum absorbance for rods was 528 nm, for single cones it was 542 nm and for twin cones it was 605 nm. Both members of the twin pair contained the same photopigment and they were electrically coupled. Under voltage clamp, the response to dim flashes of light in both single and twin cones was biphasic. The initial peak was followed by a smaller amplitude undershoot. Single cones reached peak in 86 ms and common twins in 50 ms. Background light desensitized the flash sensitivity in all photoreceptor types, but was most effective in rods and least effective in fast twins. In the steady state, the desensitizing effect of a background intensity,Ib, at the respective optimum wavelength for each cell was well described by the Weber-Fechner law (1/(1 +Ib/Ibo)), whereIbowas, on average (in units of photons/μm2/s), 1.45 for rods, 1.81 x 103for single cones, 4.56 x 103for common twins, and 6.79 x 104for fast twins.
Visual cortex damage-induced growth of retinal axons into the lateral posterior nucleus of the cat
Authors: Payne Bertram R. , Foley Heather A. , Lomber Stephen G.
Published: June 2009

Ablation of visual cortical areas 17 and 18 in neonatal and young adult cats induces novel retinal projections to terminate bilaterally in the lateral posterior nucleus (LP) at a position ventromedial from the medial interlaminar nucleus. Comparison with the visual-field maps of LP indicate that the terminations are focussed on the representation of the visual-field center.
Evidence of photoreceptor migration during early foveal development: A quantitative analysis of human fetal retinae
Authors: Diaz Araya Claudia , Provis Jan M.
Published: June 2009

We have analyzed aspects of photoreceptor topography in wholemounts of human fetal retinae in the age range 13–24 weeks of gestation. Fetal retinae were stained with cresyl violet and the sizes and packing densities of rods and cones analyzed in the conventional manner.

Cones and rods were present within a differentiating region, free of mitotic figures and approximately centered on the putative fovea, represented by the foveal cone mosaic. At 13 weeks of gestation the foveal cone mosaic was clearly differentiated, cone nuclei reaching a packing density of 14,200 per mm; a small number of rods were present in the immediately adjacent region. The packing densities of both rods and cones in these regions gradually increased and the area of the foveal cone mosaic gradually decreased throughout the age range sampled, although individual variations were evident. By 24 weeks of gestation, cone density was approximately 38,000 per mm in the foveal cone mosaic. The maximum rod density observed was 59,200 per mm in the region surrounding the foveal cone mosaic in a specimen of 20–21 weeks of gestation. In all specimens, maximum cone density occurred within the foveal cone mosaic and gradually declined towards the periphery of the differentiating region; a pronounced inverse relationship between cone soma diameter and packing density was also observed. The evidence strongly suggests that both rods and cones migrate centripetally, that is towards the center of the developing fovea, from early in development, possibly from the time that they first differentiate. The implications of these findings for fovealdevelopment are discussed.