bluuebunny/crossref_metadata_2025 huggingface dataset:
Endogenous dopamine and cyclic events in the fish retina, I: HPLC assay of total content, release, and metabolic turnover during different light/dark cycles
Authors: Kolbinger Walter , Kohler Konrad , Oetting Heike , Weiler Reto
Published: June 2009

In this study, we investigated the potency of dopamine for being an intrinsic signal for cyclic events in the fish retina. Dopaminergic activity was measured during different light/dark cycles, during continuous darkness, and during short-term light and dark adaptation within 1 h. During a 12-h light/12-h dark cycle, the total content of endogenous dopamine was high during the dark phase and low during the light phase. The potassium-induced release of endogenous dopamine followed a parallel time course. The concentration of the dopamine breakdown product 3,4-dihydroxyphenylacetic acid (DOPAC), which reflects the endogenous dopaminergic activity, was high during the light phase and low during the dark phase. Similar alterations occurred in accelerated 6-h light/6-h dark cycles, again indicating a strong coupling of dopaminergic activity with light. The cyclic alterations in the total endogenous dopamine content persisted during continuous darkness after an entrainment of the fish to a 12-h light/12-h dark cycle. Although the magnitude of the change was weaker, changes in dopamine content, potassium-induced dopamine release, and DOPAC were also measured during 1 h of light or dark adaptation. During a 1-h period of dark adaptation, the total content of dopamine and the potassium-induced release of endogenous dopamine increased, while DOPAC values decreased. These values changed in the opposite direction during 1 h of light adaptation.

Our findings strongly suggest that dopamine is the intrinsic signal for light during both the light and dark phases and during short-term adaptation. Light seems to be the major trigger for dopaminergic activity within the fish retina. An endogenous clock might participate in the control of the dopaminergic activity. This has to be, however, confirmed by further investigations.
Red/green opponency in the rhesus macaque ERG spectral sensitivity is reduced by bicuculline
Authors: Mills Stephen L. , Sperling Harry G.
Published: June 2009

Spectral-sensitivity curves were derived from the a−, b−, and d−waves of rhesus monkey ERGs after injection of bicuculline, strychnine, or no drug. Without drug injection, the a− and d−wave curves were well-fit by an additive model of weighted photoreceptor absorption spectra, while the b−wave curve requires inhibitory terms to produce an adequate fit. Bicuculline, but not strychnine, reduced the weight assigned to the inhibitory terms in a dose-dependent fashion, to the point that no inhibition was evident. The results suggest that GABAergic synapses are required for the expression of red/green color opponency in primate bipolar cells.
Effects of brief monocular deprivation on binocular depth perception in the cat: A sensitive period for the loss of stereopsis
Authors: Timney Brian
Published: June 2009

The period of susceptibility for binocular depth vision was studied in kittens by subjecting them to periods of monocular deprivation beginning at different ages. In an initial study, we found that normally reared kittens can learn a depth-discrimination task much more rapidly when tested binocularly than monocularly, even when testing is begun as early at 30 d. In subsequent experiments, kittens were monocularly deprived by eyelid suture, following which their monocular and binocular depth thresholds were measured using the jumping-stand procedure. We obtained the following results: (1) When monocular deprivation is applied before the time of natural eye opening but is discontinued by no later than 30 d, there is very Little effect on binocular depth thresholds. (2) When deprivation is begun at 90 d, binocular depth thresholds are unaffected. (3) When deprivation is begun between these two ages, the magnitude of the deficit varies with the period of deprivation and the age at which it begins. (4) By imposing brief (5 or 10 d) periods of deprivation, beginning at different ages, we were able to demonstrate that the peak of the sensitive period is between the ages of 35 and 45 d, with a fairly rapid decline in susceptibility outside those age limits. (5) Even with as little as 5 d of deprivation, substantial permanent deficits in binocular depth vision can be induced.
Morphology and distribution of serotonin-like immunoreactive amacrine cells in the retina of Bufo marinus
Authors: Zhu Baosong , Straznicky Charles
Published: June 2009

Using an antibody against serotonin (5-hydroxytryptamine, 5-HT), serotonin-like immunoreactive (serotonin IR) neurons were demonstrated in the retina of adultBufo marinus. All immunoreactive neurons were identified as amacrine cells (ACs). The dendrites of serotonin-IR ACs branched diffusely and densely throughout all levels of the inner plexiform layer (IPL) of the retina. The great majority of these cell somata were located in the vitread part of the inner nuclear layer (INL) and a few of them (ranging from 9–29 cells) were displaced into the ganglion cell layer (GCL). On the basis of the soma sizes, two populations of serotonin-IR ACs, large (type A) and small (type B), were distinguished. 6-Hydroxydopamine (6-OHDA) injected into the eye abolished immunoreactivity in the recently reported tyrosine hydroxylase (TH)-IR ACs (Zhu & Straznicky, 1990), whereas serotonin-IR ACs remained unaffected.

The number of serotonin-IR cells per retina ranged from 23,750–27,390, with a ratio of 1:1.6 to 1:1.9 between type A and B cells. Both cell types were distributed nonuniformly across the retina. Cell densities were slightly lower in the peripheral (96 cells/mm2) than in the central (164 cells/mm2) retina. Linear regression analysis confirmed the presence of a decreasing density gradient from the retinal center to the retinal margin for both small and large cell types. The analysis of the nearest neighbor distances showed that the retinal distribution of serotonin-IR ACs was orderly.

These results have been taken to indicate that 5-HT-IR cells correspond to a population of serotonincontaining ACs. It is suggested that dopamine and serotonin are contained in two different populations of ACs in the rtina ofBufo marinus.
Endogenous dopamine and cyclic events in the fish retina, II: Correlation of retinomotor movement, spinule formation, and connexon density of gap junctions with dopamine activity during light/dark cycles
Authors: Kohler Konrad , Kolbinger Walter , Kurz-Isler Gertrud , Weiler Reto
Published: June 2009

In the fish retina, retinomotor movement, spinule formation, and alteration of connexon density within gap junctions occur in response to changes in ambient light conditions. All of these morphological parameters can also be influenced by the application of dopamine. This study examines whether the morphological alterations of these structures are correlated with the activity of endogenous dopamine during an entrained 12-h light/12-h dark cycle and after 1-h sort-term adaptation periods.

The two measured parameters of retinomotor movement, cone inner segment length and pigment dispersion, were well-correlated with endogenous cyclic dopamine activity. However, retinomotor movement was initiated already at the end of the entrained dark period, before the onset of light and before the onset of dopamine turnover. Furthermore, a 1-h dark-adaptation period in the middle of the light phase reduced dopamine activity but did not affect retinomotor movement. At the switch from light to dark and after a 1-h light period at midnight retinomotor movement correlated exactly with dopamine turnover and illumination conditions. The formation of spinules was correlated with dopaminergic activity during all phases of the light/dark cycle and during short-term adaptation periods. Spinules were expressed in the light when dopamine activity was high and they were retracted when dopamine activity was reduced during darkness. Connexon density of horizontal cell gap junctions showed a weaker correlation with the endogenous dopamine turnover. In this case, a high activity of endogenous dopamine was paralleled by a high density of connexons.

Our results suggest that endogenous dopamine is involved in the cyclic regulation of the observed morphological alterations and that dopamine is part of the light signal for these mechanisms.
Postsynaptic potentials and morphology of tectal cells responding to electrical stimulation of the bullfrog nucleus isthmi
Authors: Wang S.R. , Matsumoto N.
Published: June 2009

Postsynaptic responses of tectal cells in the bullfrog (Rana catesbeiana) were intracellularly recorded following electrical stimulation of the optic tract and the nucleus isthmi, and fluorescent dye, Lucifer yellow, was injected into some of the impaled cells to show their morphologies. Two main response types were found: The first type was an EPSP followed by an IPSP, and the second type was single IPSP. The first type predominates in cells responding to the optic tract stimulation and the second type prevails in cells responding to the isthmic stimulation. Fifteen cells stained with Lucifer yellow were localized in layer 6 (11 cells), layer 7 (1 cell), and layer 8 (3 cells). They were mainly identified as pear-shaped cells, large ganglionic cells, and stellate cells. Three injections demonstrated “dye-coupling,” which labeled up to six cells following one injection. Comparisons of postsynaptic potentials with cellular morphologies suggested that the nucleus isthmi could directly excite large ganglionic neurons in layer 6. Synaptic mechanisms for strong isthmic inhibition on the tectal neurons remain unknown.
A neural and computational model for the chromatic control of accommodation
Authors: Flitcroft D. I.
Published: June 2009

Accommodation is more accurate with polychromatic stimuli than with narrowband or monochromatic stimuli. The aim of this paper is to develop a computational model for how the visual system uses the extra information in polychromatic stimuli to increase the accuracy of accommodation responses. The proposed model is developed within the context of both trichromacy and also the organization of spatial and chromatic processing within the visual cortex.

The refractive error present in the retinal image can be estimated by comparing image quality with and without small additional changes in refractive state. In polychromatic light, the chromatic aberration of the eye results in differences in ocular refractive power for light of different wavelengths. As a result, the refractive state of the eye can be estimated by comparing image quality in the three types of cone photoreceptor. The ability of cortical neurons to perform such comparisons on image quality with a crude form of spatial-frequency analysis is examined theoretically. It is found that spatially band-pass chromatically opponent neurons (that may correspond to double opponent neurons) can perform such calculations and that chromatic cues to accommodation are extracted most effectively by neurons responding to spatial frequencies of between 2 and 8 cycles/deg.
Relationship between preferred orientation and ordinal position in neurones of cat striate cortex
Authors: Vidyasagar T. R. , Henry G. H.
Published: June 2009

Striate cortical cells were classified according to whether or not their preferred orientation was close to one of the “primary” orientations (horizontal, vertical or radial, i.e. directed to the area centralis) and according to their ordinal position on the afferent pathway from the dorsal lateral geniculate nucleus (dLGN). Among the neurones that could be driven monosynaptically from the dLGN, there was a high representation of those with a preference for the primary orientations. This was particularly evident in the case of C (complex) cells. There was no such preponderance of primary orientations among the polysynaptically activated cells. It is proposed that the asymmetry of distribution seen among the first-order cells reflects the asymmetry seen subcortically in neurones that show orientation biases. It may be that the cortex elaborates a more uniform representation of orientations only at the higher ordinal levels.
Depth perception and cortical physiology in normal and innate microstrabismic cats
Authors: Distler C. , Hoffmann K.-P.
Published: June 2009

Evidence is presented that innate microstrabismus and abnormal cortical visual receptive-field properties can occur also in cats without any apparent involvement of the Siamese or albino genetic abnormalities in their visual system. A possible cause for microstrabismus in these cats may be sought in an abnormally large horizontal distance between blind spot and area centralis indicated by a temporal displacement of the most central receptive fields on both retinae.

Depth perception was found to be impaired in cats with innate microstrabismus. Behavioral measurements using a Y-maze revealed in four such cats that the performance in recognizing the nearer of two random-dot patterns did not improve when they were allowed to use both eyes instead of only one. The ability of microstrabismic cats to perceive depth under binocular viewing conditions only corresponded to the monocular performance of five normal cats.

Electrophysiological recordings were performed in the visual cortex (areas 17 and 18) of four awake cats, two normal, and two innate microstrabismic animals. Ocular dominance and orientation tuning of single neurons in area 17 and 18 were analyzed quantitatively.

The percentage of neurons in area 17 and 18 which could be activated through either eye was significantly reduced to 49.7% in the microstrabismic animals when compared to the normal cats (74.8%). “True binocular cells,” which can only be activated by simultaneous stimulation of both eyes, were significantly less frequent (1.6%) in microstrabismic cats than in normal animals (10.4%). However, subthreshold binocular interactions were identical in both groups of animals. In the strabismic animals, long-term binocular stimulation of monocular neurons did not give a clear indication of alternating use of one or the other eye.

The range of stimulus orientations leading to discharge rates above 50% of the maximal response, i.e. the half-width of the orientation tuning curves, was the same in the two groups of cats. However, orientation sensitivity, i.e. the alternation in discharge rate per degree change in stimulus orientation, was higher in cortical cells of normal cats than in those of microstrabismic cats.

In normal and microstrabismic cats, no clear sign of an “oblique effect,” i.e. the preference of cortical neurons for vertical and horizontal orientations compared to oblique orientations, could be found neither in the incidence of cells with horizontal or vertical preferred orientation nor in the sharpness of orientation tuning and sensitivity of these neurons.

In summary, the receptive-field properties reported here for awake innate microstrabismic cats are similar to those reported in the literature for anesthetized cats with varying degrees of albinism and for cats with artificial symmetrical strabismus surgically induced by sectioning the equivalent extraocular muscles in both eyes. Our innate microstrabismic cats may provide, however, an animal model for investigating the etiology of one form of naturally occurring strabismus.
Effect of monocular enucleation or impulse blockage on gamma-aminobutyric acid and cytochrome oxidase levels in neurons of the adult cat lateral geniculate nucleus
Authors: Luo X. G. , Kong X. Y. , Wong-Riley M. T. T.
Published: June 2009

Much attention has been paid to the effect of various types of neonatally induced retinal insults on neurons of the cat lateral geniculate nucleus (LGN). Little is known about cellular adjustment to functional altertions commencing in the adult. The present study was aimed at examining the effect of monocular enucleation or retinal impulse blockade on mature neurons of the cat LGN and perigeniculate nucleus. In addition to labeling the relay neurons with cytochrome oxidase (CO) histochemistry and immunohistochemistry, and presumed interneurons with GABA immunohistochemistry, the two markers were also combined in the same section. The results showed that GABA-immunoreactive neurons in the LGN can be subdivided into two major groups: highly immunoreactive neurons (Hir) and moderately immunoreactive neurons (Mir). These two groups differed slightly in their size and CO levels. With monocular enucleation or TTX treatment, there was a reduction in the numerical density of Hir and a concomitant increase in Mir in the affected laminae. However, there was no evidence of a reduction in GABA immunoreactivity in neurons of the perigeniculate nucleus. With regard to relay cells our data were in agreement with our previous findings (Kageyama & Wong-Riley, 1985) that there was a statistically significant positive correlation between cell size and CO levels, so that neurons with large cross-sectional areas were predominately darkly reactive for CO (Dco), while medium-to-small neurons were mainly moderate to lightly reactive (M/Lco). After monocular enucleation or TTX injections, the numerical density and size of Dco were significantly reduced, while those of M/Lco were proportionally increased in the affected laminae, indicating a conversion of some Dco to M/Lco. The results indicate that the maintenance of CO levels in predominately the large relay cells and GABA levels in a subclass of small neurons of the mature cat LGN are activity-dependent and are highly sensitive to retinal insults.
Neuroactive peptides as markers of retinal ganglion cell populations that differ in anatomical organization and function
Authors: Kuljis Rodrigo O. , Karten Harvey J.
Published: June 2009

Recent immunocytochemical studies indicate the existence of several classes of peptide- (PRGC) and catecholamine-containing retinal ganglion cells in anurans, birds, and mammals. Different classes of PRGC project to discrete and seemingly unique layers in the retino-recipient portion of the anuran and avian optic tectum. Peptide-containing retinofugal projections to the frog tectum originate early in development, and are reestablished by some classes of PRGC during regeneration of the optic nerve. These findings indicate that chemically specific, parallel retinofugal pathways presumably subserve different functional aspects of vision in vertebrates. Exciting prospects for research include the correlation of physiologically with immunocytochemically defined classes of retinal ganglion cells, the analysis of the possible role of neuroactive peptides in retinofugal transmission, and the pharmacological manipulation of putative peptidergic retinofugal pathways to analyze their role in visual function.
Nonuniform retinal expansion during the formation of the rabbit's visual streak: Implications for the ontogeny of mammalian retinal topography
Authors: Robinson Stephen R. , Dreher Bogdan , McCall Murray J.
Published: June 2009

We have studied the distribution of retinal ganglion cells (RGCs) which have been retrogradely labeled from massive bilateral injections of the enzyme horseradish peroxidase into the retino-recipient nuclei of foetal and postnatal albino rabbits aged from the 24th postconceptional day (24PCD) to adulthood. The number of labeled RGCs increases from about 447,000 on the 24PCD to a peak of about 525,000 on the 27PCD. From the 29PCD to birth (31/32PCD), the number of RGCs rapidly declines to about 375,000. During the next 20 d, the number of RGCs stabilizes at about 335,000. After the 51PCD, the number of RGCs gradually declines to the adult value of about 280,000. Retinal area steadily increases from about 40 mm2 on the 24PCD to about 500 mm2 in the adult, while RGC density decreases. However, the reduction in RGC density is nonuniform: RGC density in the visual streak drops from 18,600 RGCs mm2 on the 24PCD to 4700 RGCs/mm2 in the adult, whereas RGC densities at the superior and inferior edges of the retina decrease proportionally much more (from 9300 to 105 RGCs/mm2 and from 12,000 to 170 RGCs/mm2, respectively). As a result of this differential reduction in RGC density, the streak:superior edge RGC density ratio changes from 2.0:1 on the 24PCD to about 45:1 in the adult, while the streak/inferior edge ratio changes from 1.6:1 to about 28:1. In the periods from the 24PCD to the 29PCD and from the 32PCD to adulthood, the proportional increases in the streak/superior edge and streak/inferior edge RGC density ratios are linearly related to the proportional increases in retinal area. However, between the 29PCD and 32PCD, the RGC density ratios increase at a greater rate than retinal area. We conclude that (1) the centro-peripheral difference in RGC density that is already present on the 24PCD might be attributable to differential RGC generation; (2) the redistribution of RGCs between the 24PCD and adulthood is mainly due to nonuniform expansion of the retina, with minimal expansion of the visual streak and maximal expansion at the superior and inferior retinal edges; and (3) a small component of the increase in the centro-peripheral RGC density ratio, which becomes apparent between the 29PCD and 32PCD, is probably due to differential RGC loss. We discuss the pattern of retinal expansion in the rabbit and the factors which might contribute to it.
The ontogeny of ultraviolet photosensitivity in rainbow trout (Salmo gairdneri)
Authors: Hawryshyn Craig W. , Arnold Margaret G. , Chaisson Duane J. , Martin Patricia C.
Published: June 2009

The present study examines the changes in ultraviolet (UV) photosensitivity that occur during the growth of rainbow trout (Salmo gairdneri). A comparison of the ocular media transmission of small (n = 3) and large (n = 3) trout eyes did not reveal large changes in the transmission of UV radiation through the eye. We used the heart-rate conditioning technique to measure spectral sensitivity in immobilized trout. Four trout, each weighing less than 30 g, exhibited a UV-sensitivity peak at 360 nm while four additional trout weighing more than 60 g each exhibited no evidence of UV sensitivity. Spectral-sensitivity measurements of two trout weighing 44 g and 60 g revealed UV sensitivity, but when measured one month later (after a 25% increase in body weight) both fish exhibited no UV-sensitivity peak. At this time their sensitivity appeared to conform to the known blue-sensitive cone mechanism.
Neurons of the medial terminal accessory optic nucleus of the rat are poorly collateralized
Authors: Clarke R. J. , Giolli R. A. , Blanks R. H. , Torigoe Y. , Fallon J. H.
Published: June 2009

The vast majority of neurons of the rat medial terminal nucleus (MTN) project to the nucleus of the optic tract (NOT), but the MTN also projects to a lesser degree upon a number of other brainstem nuclei controlling optokinetic nystagmus. Because of the diversity of targets of the MTN, it is possible that individual neurons have branched axons that project to two or more brainstem nuclei. The possibility that axons of MTN-NOT neurons collateralize to innervate other MTN targets is examined in the rat with the fluorescent, double-labeling, retrograde tracer technique. Fluoro-Gold was injected into the NOT while Fast Blue was simultaneously injected into each of five other known targets of the MTN: the supraoculomotor-periaqueductal gray; the dorsal cap of the inferior olive; the visual tegmental relay zone; the dorsolateral nucleus of the basal pons; and the superior/lateral vestibular nuclei. Brainstem sections were processed for fluorescence microscopy and the MTN was examined for single- and double-labeled neurons. Results show that virtually all neurons of the MTN (>97.5%), together with neurons in the visual tegmental relay zone immediately surrounding the MTNd, are single-labeled in all paired injections involving the NOT and the other target nuclei. It was found that about 69% of MTN neurons project exclusively to the NOT, 5–10% project to each one of the other nuclei, and 3% of MTN neurons project to more than one target. Based upon cell counts from the fluorescent material, and previous analysis of Nissl-stained serial sections, the findings show that virtually all MTN neurons are projection neurons. It was concluded that the MTN is comprised of independent projection systems, possibly involved in different aspects of generating optokinetic nystagmus.
Cortical interactions in texture processing: Scale and dynamics
Authors: Victor Jonathan D. , Conte Mary M.
Published: June 2009

We investigate the neural computations underlying pattern processing with stimuli based on textures balanced for spatial frequency content (and second-order correlations) but not for higher-order correlations (Julesz et al. 1978). Interchange between two such isodipole textures produces a robust human visual evoked potential (VEP). The difference in population activity driven by two isodipole textures is quantified by the antisymmetric component of the VEP. Statistical properties of the textures eliminate contributions from linear mechanisms to the antisymmetric VEP.

The dependence of the antisymmetric VEP on check size and fourth-order correlation statistics is used to test nonlinear models for the underlying neural computations. Linear summation, followed by a simple nonlinearity (such as rectification, saturation, or threshold), is inconsistent with the data. More elaborate models, in which a second nonlinear stage combines the output of local nonlinear mechanisms, are consistent with the data, provided that an appropriate spatial scale is chosen for the second stage of processing. For checks 4 min or smaller, the deduced interaction length is 10–15 min. For checks larger than 4 min, the interaction length is proportional to check size.
Protein Kinase C-like immunoreactivity in rod bipolar cells of the rat retina: A developmental study
Authors: Zhang Danru , Yeh Hermes H.
Published: June 2009

In the retina of a variety of vertebrate species, a monoclonal antibody against protein kinase C (PKC) has been shown to label preferentially bipolar cells. Although the functional consequences of PKC activation in these cells is yet to be revealed, the present study was motivated in part by the possibility that the antibody might be used as a selective marker for examining the development of bipolar cells in the rat retina. Here, the developmental pattern and the dynamic changes of retinal cells expressing PKC-like immunoreactivity (PKC-LI) were studied and analyzed throughout postnatal life until adulthood. Upon its initial detection by immunohistochemistry on postnatal day (PD)-10, faint PKC-LI was limited to the central region of the retina, labeling cell bodies located at the scleral margin of the inner nuclear layer (INL) adjacent to the outer plexiform layer (OPL). On subsequent days, PKC-LI spread progressively to the peripheral retina and axon terminal bulbs at the vitreal margin of theinner plexiform layer (IPL) began showing the first signs of immunoreactive labeling. Not until PD-15, the time of eye opening, did PKC-LI in these cells increase to the extent such that their thin axons were immunoreactive. Each of these axons traversed the entire thickness of the IPL and divided into two or three short branches before ending as enlarged terminal bulbs. The morphology and the location of PKC-LI cells in both the developing and adult retina observed in our study are consistent with them being rod bipolar cells. By the end of the fourth postnatal week, the rod bipolar cells appeared mature, resembling those found in the adult. Overall, more dynamic changes occurred at the axon terminal bulbs than at the cell bodies during the maturational process of rod bipolar cells. Interestingly, PKIC-LI was expressed precociusly in these cells when rat pups were reared in complete darkness starting from the day of birth.
Synchronous neurite branchings in single goldfish retinal ganglion cells
Authors: Ishida A. T. , Cheng M.- H.
Published: June 2009

We have examined the time course of branch formation in neurites of retinal ganglion cells isolated from adult goldfish (Carassius auratus). These neurites elongate at approximately 13 μm/h, and usually branch by bifurcation of growth cones at their tips. The times elapsed between branchings in different neurites of single cells can be described by a Poisson distribution with a mean interval of approximately 2 h. As predicted by this distribution, a relatively large number of branchings occur simultaneously in different neurites of individual cells. Simultaneous branchings of neurites elongating at a common rate generate branch points that lay equidistant from their soma. Since similar branching patterns can be seen in dendrites of retinal ganglion and amacrine cellsin situ, these results are consistent with the possibility that dendrites of individual neurons branch synchronously and grow at common rates during development.
Spectral sensitivity of the electroretinogram b-wave in dark-adapted goldfish
Authors: Nussdorf Jonathan D. , Powers Maureen K.
Published: June 2009

The action spectrum of the ERG b-wave was measured under dark-adapted conditions in intact goldfish (Carassius auratus). It is substantially broader than the absorption spectrum of goldfish rod porphyropsin. Neither prolonged dark adaptation nor removal of possible efferent neural activity affected its shape. Moreover, a 682-nm background did not produce a selective loss of sensitivity to long wavelengths. The results imply that the spectral sensitivity of the b-wave in dark-adapted goldfish reflects the influence of at least two photoreceptor types which act as a single univariant mechanism near absolute threshold.
Laminar organization and ultrastructure of GABA-immunoreactive neurons and processes in the dorsal lateral geniculate nucleus of the tree shrew (Tupaia belangeri)
Authors: Holdefer Robert N. , Norton Thomas T. , R. Ranney Mize
Published: June 2009

The distribution and ultrastructure of neurons and neuropil labeled by an antiserum to gamma-aminobutyric acid (GABA) were examined in the lateral geniculate nucleus (LGN) of the tree shrew (Tupaia belangeri). The LGN of this species segregates center type and cell class into three distinct pairs of laminae: a medial pair (laminae 1 and 2) containing ON-center cells, a more lateral pair (4, 5) containing OFF-center cells, and 2 laminae (3, 6) containing W-like cells. The relationship between this laminar segregation and the distribution of GABA immunoreactivity was investigated in the present study. GABA-immunoreactive neurons and neuropil were present in all six of the laminae. However, both the density of labeled cells (adjusted for neuronal density across laminae) and the density of labeled neuropil showed a medial-to-lateral gradient. The adjusted density of labeled cells was higher laterally than medially, and the density of labeled neuropil was significantly greater in the more lateral OFF-center laminae and W-like laminae than in the medial two ON-center laminae. Thus, inhibitory, GABAergic influences may modulate to different degrees the visual signals in the ON, OFF, and W pathways. Labeled cells had a mean cross-sectional area (107 μm2) approximately one-half that of unlabeled cells (216 μm2). They constitute 16–34% of the neurons in the LGN. At the electron microscope level, three different kinds of labeled profile were observed. Vesicle containing profiles like the F2 profiles of cat were postsynaptic to retinal terminals and presynaptic to conventional dendrites. Fl axon terminals with dense clusters of vesicles were also labeled as were some myelinated axons. Another labeled profile, which we suggest should be called an F3 process, was a large dendrite of irregular caliber with punctate groups of vesicles near the synapse. Our results suggest that GABAergic circuitry is an important part of the functional organization in the LGN of the tree shrew.
Regeneration of the dopamine-cell mosaic in the retina of the goldfish
Authors: Hitchcock Peter F. , Vanderyt Jeff T.
Published: June 2009

A fundamental anatomical feature of retinal neurons is that they form planar mosaics. Each mosaic can be described by its density, pattern, and regularity (non-randomness). As part of ongoing studies to quantitatively describe the anatomy of regenerated retina in the goldfish, we determined the planimetric density and regularity of the mosaic of dopaminergic interplexiform cells in patches of regenerated retina and compared this to the mosaic generatedde novo.In addition, we selectively ablated dopaminergic neurons with the neurotoxin 6–hydroxydopamine (6–OHDA) before inducing local regeneration and determined whether or not the absence of the extant dopaminergic neurons modulated the planimetric density or number of regenerated ones. The results showed that dopaminergic neurons are regenerated at higher planimetric densities and in less orderly arrays than normal. Furthermore, there was no statistical difference in the density or number of regenerated cells in normal retinas and retinas treated with 6–OHDA.
Steady discharges of X and Y retinal ganglion cells of cat under photopic illuminance
Authors: Troy J.B. , Robson J.G.
Published: June 2009

The discharges of ON- and OFF-center X and Y retinal ganglion cells in the presence of stationary patterns or of a uniform field of photopic luminance were recorded from urethane-anesthetized adult cats. The interval statistics and power spectra of these discharges were determined from these discharge records. The patterned stimuli were selected and positioned with respect to a cell's receptive field so as to generate steady discharges that were different in mean discharge rate from that cell's discharge for the diffuse field. The interval statistics of discharges recorded for diffuse or patterned illumination for all cell types can be modeled, approximately, as coming from renewal processes with gamma-distributed intervals. The gamma order of the interval distributions was found to be nearly proportional to the mean discharge rate for X cells, but not for Y cells. Typical values for the gamma orders and their dependence on mean rate for different cell types are given. The same model of a renewal process with gamma-distributed intervals is used to model the measured power spectra and performs well. When the gamma order is proportional to mean rate, the power spectral density at low temporal frequencies is independent of discharge rate. Gamma order was proportional to mean rate for X cells but not for Y cells. Nonetheless, the power spectral densities of both cell types at low frequencies were approximately independent of discharge rate. Hence, noise in this band of frequencies can be considered additive. The consequences of departures from the renewal process and of the gamma order not being proportional to mean rate are considered. The significance of different rates of discharge for signaling is discussed.
ATP-independent deactivation of squid rhodopsin
Authors: Kahana Alon , Robinson Phyllis R. , Lewis Laura J. , Szuts Ete Z. , Lisman John E.
Published: June 2009

Deactivation of light-activated squid rhodopsin was studiedin vitrousing GTPγS binding by G-protein as a direct measure of rhodopsin activity. Deactivation was inhibited by dilution of the retinal suspension or by removal of soluble components. Deactivation could be restored by addition of soluble material to washed membranes. These results indicate that the deactivation is not due entirely to a conformational transition within rhodopsin itself, but depends on the interaction with other molecules. The possibility that phosphorylation is involved in the deactivation was studied. Deactivation occurred in the presence and absence of added ATP. Deactivation also occurred in the presence of kinase inhibitors and after addition of apyrase, which reduced residual ATP levels to below 1μM. These results indicate that light-induced phosphorylation is not required for deactivation of squid rhodopsin. In this regard deactivation of squid rhodopsin is different from that of vertebrate rhodopsin, which requires phosphorylation.
White-noise analysis in visual neuroscience
Authors: Sakai Hiroko M. , Ken-Ichi Naka , Korenberg Michael J.
Published: June 2009

In 1827, plant biologist Robert Brown discovered what is known as Brownian motion, a class of chaos. Formal derivative of Brownian motion is Gaussian white-noise. In 1938, Norbert Wiener proposed to use the Gaussian white-noise as an input probe to identify a system by a series of orthogonal functionals known as the Wiener G-functionals.

White-noise analysis is uniquely suited for studying the response dynamics of retinal neurons because (1) white-noise light stimulus is a modulation around a mean luminance, as are the natural photic inputs, and it is a highly efficient input; and (2) the analysis defines the response dynamics and can be extended to spike trains, the final output of the retina. Demonstrated here are typical examples and results from applications of white-noise analysis to a visual system.
Contributions to the electroretinogram of currents originating in proximal retina
Authors: Frishman Laura J. , Sieving Paul A. , Steinberg Roy H.
Published: June 2009

We have investigated responses in proximal retina of the cat that contribute to two kinds of electroretinogram (ERG) recordings: (1) the pattern ERG, a light-adapted response and (2) the threshold and near threshold ERG, a dark-adapted response (Sieving et al., 1986a, 1986b; Sieving & Steinberg, 1985). In intraretinal, extracellular recordings, two negative-going responses were identified that are maximal around the inner plexiform layer, and distinct from PII, which is maximal in distal retina: under light-adapted conditions, a spatially tuned response at light onset and light offset, the “M-wave” (previously described in cold-blooded animals by Karwoski & Proenza (1977, 1980)), and under dark-adapted conditions, the scotopic threshold response, or “STR,” a response at light onset. The results under dark-adapted conditions are examined in more detail here.

The STR is a very sensitive response whose threshold is 1.5–2.0 log units below that of the dc-component of PII and therefore well below the threshold of the a-, b-, and c-waves. It saturates about 2.4 log units below rod saturation. The STR contributes a negative-going potential to the dark-adapted ERG that is dominant near threshold; while PII (dc-component and b-wave) contributes a positive-going potential that is dominant at higher intensities (Sieving et al., 1986b). Investigation of the mechanism of the proximal retinal responses that contribute to the ERG supports a K+-Müller cell hypothesis of their origin.
Immunocytochemical localization of glycine in the retina of the turtle (Pseudemys scripta)
Authors: Eldred William D. , Cheung Kristin
Published: June 2009

We have localized glycine-like immunoreactivity to provide new anatomical detail about glycinergic neurons in the turtle retina. A rabbit antiserum directed against a glycine/albumin conjugate was used with standard fluorescent and avidin-biotin labeling techniques. Some processes in the outer plexiform layer and many processes in the inner plexiform layer, numerous somata in the inner nuclear layer, and isolated somata in the ganglion cell layer were immunoreactive.

The vast majority of labeled neurons were amacrine cells. One class of amacrine cells had well-labeled somata near the inner nuclear/inner plexiform layer border, which gave rise to thick primary processes that entered the inner plexiform layer and arborized near the border of strata 1 and 2 and in stratum 3. A second class of glycinergic neurons, consisting of putative interplexiform cells, was unique in that it gave rise to dendritic arborizations in both the outer plexiform layer and the inner plexiform layer. Some of the immunoreactive neurons in the ganglion cell layer were apparently displaced amacrine cells, while others were probably true ganglion cells because they gave rise to labeled axons, and many labeled axons were visible in the ganglion cell axon layer. These results suggested that glycine played an extensive role in the turtle retina, and that it was involved in many diverse synaptic interactions in both the outer plexiform layer and the inner plexiform layer.
Involvement of ON and OFF retinal channels in the eye and head horizontal optokinetic nystagmus of the frog
Authors: Yücel Y. H. , Jardon B. , Bonaventure N.
Published: June 2009

The specific role of ON and OFF retinal information channels in the generation of the horizontal optokinetic nystagmus (OKN) of the frog was studied. Coil recordings of monocular eye and head OKN were obtained before and after intravitreal injection of two drugs that block either ON or OFF channels. The intravitreal injection of 2-amino-4-phosphonobutyrate (APB), a glutamate analog that selectively blocks the ON retinal channel, strongly reduced or even cancelled the monocular OKN of the head and of the eye. The intravitreal injection of another glutamate analog, the cis-2, 3-piperidine dicarboxylic acid (PDA) that especially blocks the OFF retinal channel, did not affect the gain velocity of the slow phase of both the horizontal monocular head and eye OKN, for low stimulus velocities. Our results suggest that the retinal ON information channel, but not the OFF channel, is involved in the generation of the slow phase of the OKN of the frog, at least at low drum velocities.
Spatial- and temporal-frequency selectivity as a basis for velocity preference in cat striate cortex neurons
Authors: Baker Curtis L.
Published: June 2009

Measurements were made of the optimal velocity for drifting bar-shaped stimuli to excite striate cortex neurons of the cat. These data were compared to the optimal spatial and temporal frequencies of the same neurons, as determined with drifting sine-wave grating stimuli. A systematic relationship was revealed, whereby those neurons preferring higher velocities of bar motion also preferred lower spatial and higher temporal frequencies of gratings. The optimal bar velocity for a given neuron could be quantitatively predicted from the ratio of that neuron's optimal temporal frequency to its optimal spatial frequency.
Effect of sawtooth polarity on chromatic and luminance detection
Authors: DeMarco Paul J. , Smith Vivianne C. , Pokorny Joel
Published: June 2009

Psychophysical studies have documented that many observers show lower thresholds for rapid-off than for rapid-on sawtooth luminance modulation. This finding, together with physiological findings from chromatically opponent ganglion cells of the macaque monkey, prompted a search for a similar bias in psychophysical detection of chromatic increments and decrements of light. Using a luminance pedestal in conjunction with a luminance background to favor detection by chromatic mechanisms, we measured spectral sensitivity for rapid-on and rapid-off sawtooth stimuli presented spatially coextensive with the pedestal. There were two different pedestal chromaticities: one broadband, and the second composed only of long-wavelength light to enhance short-wavelength-sensitive, cone-mediated detection. Spectral-sensitivity measurements for different wavelength stimuli revealed no systematic differences across the visible spectrum as a function of sawtooth waveform polarity or pedestal chromaticity. Similarly, temporal contrast-sensitivity functions for hetero-chromatically modulated red-green sawtooth stimuli did not reveal an asymmetry in sensitivity for rapid-red and rapid-green chromatic change. Some of the observers showed a higher sensitivity for luminance modulated rapid-off sawtooth stimuli, as also noted in previous studies. This asymmetry was not found when a white luminance pedestal and background was used. These results suggest that the cone inputs to chromatically opponent ON- and OFF-center cells are sufficiently balanced to provide equivalent psychophysical thresholds for chromatic increments and decrements of light.
Evidence for two systems mediating perceived contrast
Authors: Brannan Julie R. , Bodis Ivan
Published: June 2009

We report psychophysical evidence for a categorical dichotomy in the perception of contrast. Observers were required to rate the contrast of sinusoidal gratings (2.3 c/d) with contrast varying over a given range relative to two standards. One standard was designated “high” contrast and the other was designated “low.” There was a boundary effect: contrast judgment depended upon whether the tested ranges included 10–15% contrast and discrimination was sharpest at the boundary between 10 and 15% contrast. These results are consistent with the existence of two systems underlying perceived contrast; one primarily sensitive below 10%, and the other primarily sensitive above 15% contrast.
Rod bipolar cells in the cone-dominated retina of the tree shrew Tupaia belangeri
Authors: Müller Brigitte , Peichl Leo
Published: June 2009

The tree shrew has a cone-dominated retina with a rod proportion of 5%, in contrast to the common mammalian pattern of rod-dominated retinae. As a first step to elucidate the rod pathway in the tree shrew retina, we have demonstrated the presence of rod bipolar cells and studied their morphology and distribution by light and electron microscopy.

Rod bipolar cells were labeled with an antiserum against the protein kinase C (PKC), a phosphorylating enzyme. Intense PKC immunoreactivity was found in perikarya, axons, and dendrites of rod bipolar cells. The cell bodies are located in the sclerad part of the inner nuclear layer, the dendrites ascend to the outer plexiform layer where they are postsynaptic to rod spherules, and an axon descends towards the inner plexiform layer (IPL). The axons branch, and terminate in the vitread third of the IPL where mammalian rod bipolar cells are known to terminate. Two amacrine cell processes are always seen as the postsynaptic elements (dyads). Dendritic and axonal arbors of rod bipolar cells are rather large, up to 100 μm in diameter. The topographical distribution of the rod bipolar cells was analyzed quantitatively in tangential sections.Their density ranges from 300 cells/mm2 in peripheral retina to 900 cells/mm2 more centrally. The distribution is rather flat with no local extremes. Consistent with the low rod proportion in tree shrew, the rod bipolar cell density is low compared to the rod-dominated cat retina for example (36,000-47,000 rod bipolar cells/mm2). Rod-to-rod bipolar cell ratios in the tree shrew retina range from smaller than 1 to about 7, and thus are also lower than in cat.
Visual telencephalon modulates directional selectivity of accessory optic neurons in pigeons
Authors: Britto Luiz R.G. , Gasparotto Odival C. , Hamassaki Dânia E.
Published: June 2009

The directional selectivity of units within the nucleus of the basal optic root (nBOR) of the accessory optic system (AOS) was studied before and after lesions of the visual telencephalon (visual Wulst) in urethane-anesthetized pigeons. In intact pigeons, most nBOR units preferred upward motion with a temporal component or downward motion with a nasal component. The ipsilateral and bilateral telencephalic lesions generated a dramatic reduction in the number of cells with optimal responses to upward motion. The overall distribution of preferred directions was still bimodal following ipsilateral or bilateral Wulst lesions, with most units showing best responses to a straight temporal or to downward-nasal directions. The contralateral Wulst lesions produced, instead, a marked reduction in downward preferences. The nBOR units which were studied in these cases showed mainly upward-temporal and upward-nasal responses. These data suggest an involvement of the visual Wulst in the determination of the dictional selectivity of nBOR neurons in the pigeon. Specifically, the responses of nBOR units to upward motion appeared to depend on the integrity of the telencephalic descending systems which impinge, in both direct and indirect ways, upon that AOS nucleus. Taken together with data for the mammalian AOS, the present results indicate that nonretinal afferents to AOS nuclei have an important role in the functional organization of that subcortical visual pathway.