bluuebunny/crossref_metadata_2025 huggingface dataset:
Organization of individual cortical axons projecting from area V1 (area 17) to V2 (area 18) in the macaque monkey
Authors: Rockland Kathleen S. , Virga Agnes
Published: June 2009

The present study uses the anterograde tracer, Phaseolus vulgaris-leucoagglutinin (PHA-L), to investigate the detailed morphology of individual axons projecting from area V1 to prestriate area V2. Observations are derived from serial reconstructions of 45 axons. Axons are found to differ both in laminar distribution and in arbor size. The majority (25/45; 56%) terminate in the upper half of layer 4 and the lower part of layer 3. Terminal clusters typically measure about 200 μm in diameter (dimensions are uncorrected for shrinkage), and are either in one, two, or occasionally three patches. Patches are separated by 200−500 μm. Of these 25 axons, four also have minor collaterals to layer 5. Of the remaining 20 axons in our sample, eight have one or two terminal arbors (about 200 μm in diameter) mainly in layer 3; another eight have terminations, organized as a single field (about 350 μm in diameter), within layer 4; and four axons have much larger terminal fields (1.0−1.2 mm × 0.3 mm), in layers 3 nd 4. These morphological differences might constitute a gradient or, alternately, indicate distinct subgroups within the striate efferent population. Large terminal fields are asymmetrical, with their long axis oriented in an anterior-posterior fashion toward the depth of the lunate sulcus. Axons with two terminal arbors have a similar bias. As this arrangement is approximately perpendicular to the border of V1, we suggest that striate axons may be extended preferentially along the length of the stripelike compartments in V2. These compartments are also arrayed perpendicular to the border between areas V1 and V2. Reconstruction of small groups of 2–4 convergent axons demonstrates that axons with different morphology (i.e. large or small terminal fields) can occur within the same projection focus. Terminal arbors belonging to different axons can overlap, but tend not to be superimposed exactly.
Immunocytochemical localization of taurine and glial fibrillary acidic protein in human optic nerve
Authors: Lake Norma , Verdone-Smith Carole , Brownstein Seymour
Published: June 2009

Taurine immunoreactivity (IR) in 1 -μm sections of glutaraldehyde-fixed human optic nerve was observed using light microscopy and an antibody raised in rabbit to taurine conjugated to bovine serum albumin. Throughout the nerve, taurine-lR was prominent in glial cells, in their perinuclear regions, and in their numerous branching processes, some of which extended to the pial septa. The peripheral glial mantle (glia limitans) was densely stained, whereas axons and the pial septa showed relatively little or no taurine-IR. Immunoreactivity for glial fibrillary acidic protein (GFAP), an astrocyte-specific marker, was evaluated on adjacent sections. The pattern of GFAP-IR was highly similar to that for taurine, suggesting that a subset of taurine-immunoreactive glial cells are optic nerve astrocytes. To our knowledge, this is the first localization of taurine and GFAP in human optic nerve.
The laminar distribution of macaque tectobulbar and tectospinal neurons
Authors: May Paul J. , Porter John D.
Published: June 2009

The superior colliculus exerts its most direct influence over orienting movements, and saccades in particular,viaits descending projections to the brain stem and spinal cord. However, while there is detailed physiological data concerning the generation of saccade-related activity in the primate superior colliculus, there is relatively little data on the detailed connectivity of this structure in primates. Consequently, retrograde transport techniques were utilized to determine the locations of the cells of origin of these descending pathways in macaque monkeys. Tectal cells that projected to the ipsilateral pontine reticular formation were mainly found in the deep gray layer and occasionally in the intermediate gray layer. Tectal cells that projected to the contralateral pontine reticular formation were predominantly located in the intermediate gray layer. The contralaterally projecting population could be subdivided into two groups. The cells in upper sublamina of the intermediate gray layer project primarily to the saccade-related regions of the paramedian reticular formation. Cells in the lower sublamina project primarily to more lateral regions of the pontine reticular formation and to the spinal cord. We conclude that the primate colliculus is provided with at least three descending output channels, which are likely to differ in their connections and functions. Specifically, it seems likely that the lower portion of the intermediate gray layer may be specialized to subserve combined head and eye orienting movements, while the upper sublamina subserves saccades.
Quantitative immunogold evidence for enrichment of glutamate but not aspartate in synaptic terminals of retino-geniculate, geniculo-cortical, and cortico-geniculate axons in the cat
Authors: Montero Vicente M.
Published: June 2009

A postembedding immunogold procedure was used on thin sections of the dorsal lateral geniculate nucleus (LGN) and perigeniculate nucleus (PGN) of the cat to estimate qualitatively and quantitatively, at the electron-microscopic (EM) level, the intensity of glutamate or aspartate immunoreactivities on identifiable synaptic terminals and other profiles of the neuropil. On sections incubated with a glutamate antibody, terminals of retinal and cortical axons in the LGN, and of collaterals of geniculo-cortical axons in the PGN, contain significantly higher density of immunogold particles than GABAergic terminals, glial cells, dendrites, and cytoplasm of geniculate cells. By contrast, in sections incubated with an aspartate antibody, terminals of retino-geniculate, cortico-geniculate, and geniculo-cortical axons did not show a selective enrichment of immunoreactivity, but instead the density of immunogold particles was generally low in the different profiles of the neuropil, with the exception of nucleoli. These results suggest that glutamate, but not aspartate, is a neurotransmitter candidate in the retino-geniculo-cortical pathways.
Two-dimensional receptive-field organization in striate cortical neurons of the cat
Authors: Sun Ming , Bonds A. B.
Published: June 2009

The two-dimensional organization of receptive fields (RFs) of 44 cells in the cat visual cortex and four cells from the cat LGN was measured by stimulation with either dots or bars of light. The light bars were presented in different positions and orientations centered on the RFs. The RFs found were arbitrarily divided into four general types: Punctate, resembling DOG filters (11%); those resembling Gabor filters (9%); elongate (36%); and multipeaked-type (44%). Elongate RFs, usually found in simple cells, could show more than one excitatory band or bifurcation of excitatory regions. Although regions inhibitory to a given stimulus transition (e.g. ON) often coincided with regions excitatory to the opposite transition (e.g. OFF), this was by no means the rule. Measurements were highly repeatable and stable over periods of at least 1 h. A comparison between measurements made with dots and with bars showed reasonable matches in about 40% of the cases. In general, bar-based measurements revealed larger RFs with more structure, especially with respect to inhibitory regions. Inactivation of lower cortical layers (V-VI) by local GABA injection was found to reduce sharpness of detail and to increase both receptive-field size and noise in upper layer cells, suggesting vertically organized RF mechanisms. Across the population, some cells bore close resemblance to theoretically proposed filters, while others had a complexity that was clearly not generalizable, to the extent that they seemed more suited to detection of specific structures. We would speculate that the broadly varying forms of cat cortical receptive fields result from developmental processes akin to those that form ocular-dominance columns, but on a smaller scale.
Calcium gradients and light-evoked calcium changes outside rods in the intact cat retina
Authors: Gallemore Ron P. , Li Jian-Dong , Govardovskii Victor I. , Steinberg Roy H.
Published: June 2009

We have studied light-evoked changes in extracellular Ca2+concentrationin the intact cat eye using ion-sensitive double-barreled microelectrodes. Two prominent changes in Ca2+concentration were observed that differed in retinal location. There was a light-evoked increase inaccompanied by brief ON and OFF transients, which was maximal in the inner plexiform layer and was not further studied. There was an unexpected sustained light-evokeddecreaseinof relatively rapid onset and offset, which was maximal in the distalmost region of the subretinal space (SRS).in the SRS was 1.0 mM higher than in the vitreous humor during dark adaptation and this transretinal gradient disappeared during rod-saturating illumination. After correcting for the light-evoked increase in the volume of the SRS, an increase in the total Ca2+content of the SRS during illumination was revealed, which presumably represents the Ca2+released by rods. To explain the light-evokedchanges, we used the diffusion model described in the accompanying paper (Li et al., 1994b), with the addition of light-dependent sources of Ca2+at the retina/retinal pigment epithelium (RPE) border and rod outer segments. We conclude that a drop inaround photoreceptors, which persists during illumination and reduces a transretinal Ca2+gradient, is the combined effect of the light-evoked SRS volume increase, Ca2+release from photoreceptors, and an unidentified mechanism(s), which is presumably Ca2+transport by the RPE. The relatively rapid onset and offset of thedecrease remains unexplained. These steady-state shifts inshould have significant effects on photoreceptor function, especially adaptation.
Actin depolymerization is not involved in phototransduction
Authors: Feng J. , Fein A.
Published: June 2009

The rhabdomeral microvilli in the eyes of invertebrates have a cytoskeletal core (Saibil, 1982; Blest et al., 1982a, b, 1983) of actin (de Couet et al., 1984; Arikawa et al., 1990; Williams, 1991; Caiman & Chamberlain, 1992) which might be involved in phototransduction. Tsukita et al. (1988) suggested that light stimulation triggers the breakdown of the microvillar actin filament complex and that this may play a role in phototransduction. To test their suggestion, we pressure-injected phalloidin into Limulus ventral photoreceptors to prevent actin depolymerization (Cooper, J.A., 1987) and tested to see if this blocked phototransduction. We have previously shown that injected rho-damine-phalloidin brightly labels the microvillar actin filaments in living Limulus ventral photoreceptors for several hours (Feng et al., 1994). In the experiments reported here, phalloidin unconjugated with fluorophore was used, and the final concentration in the cell after many small injections from a pipette containing 10 mg/ml phalloidin was estimated to be 1 mg/ml (1.2 mM). This concentration is 100 times higher than that used in an extracted cellular preparation to stabilize actin (Biegel & Pachter, 1992). Fig. 1 shows that the responses to steps of light at different intensities are normal 1 h after phalloidin injection. Similar results were obtained in two other cells.
Effect of disparity in the peripheral field on short-latency ocular following responses
Authors: Kawano K. , Inoue Y. , Takemura A. , Miles F. A.
Published: June 2009

Ocular following responses induced by brief movements of the visual scene were examined in monkeys for their dependence on disparity in the peripheral field. A random dot pattern was projected onto a tangent screen and partitioned into central and peripheral regions. Test stimuli were velocity steps applied in the central region, while stimuli in the periphery were stationary. The visual images in the central region were seen always in the plane of the screen, while stimuli in the periphery could be seen in front, behind, or in the plane of the screen (achieved by a system of polarizing filters). Initial ocular following responses were larger when the peripheral stimuli were presented with an uncrossed disparity than without disparity. On the other hand, responses were smaller when the peripheral stimuli were presented with crossed disparity (<5.0 deg) than without disparity. The result is consistent with the idea that ocular following responses are dependent on the perceived viewing distance.
Response properties of ganglion cells in the isolated mouse retina
Authors: Stone Charlene , Pinto Lawrence H.
Published: June 2009

We have studied the organization of receptive fields of ganglion cells in the isolated mouse retina and have shown that the organization is similar to that of the cat. Based upon responses to circular and annular stimuli, most ganglion cells (90%; N = 83) had receptive fields with concentric center-surround organization, either ON or OFF center. The plot of response amplitude vs. stimulus area for these cells increased to a maximum (corresponding to a diameter of 10.0 ± 2.8 deg S.E.M.; N = 13) and then decreased for larger stimuli, demonstrating the presence of an antagonistic surround. The dark-adapted sensitivity (205 ± 43.8 impulses quantum−1 rod−1; mean ± S.E.M.) did not differ from that measured for the intact preparation. We found a subset of OFF-center cells for which the dark discharge was very regular (mean coefficient of variation = 0.30). Using sinusoidal grating stimuli, we classified ganglion cells as X-like (87%) and Y-like (13%) based on spatial summation properties and the presence of subunit activity in the receptive-field center. We found no difference in the spatial-frequency preference between X-like and Y-like cells in the central retina (high cutoff frequency, 0.20 ± 0.014 cycle/deg, mean ± S.E.M.), in contrast to the marked difference between X cells and Y cells in the cat. Thus, ganglion cell receptive fields in the mouse retina resemble those of the cat, although the spatial characteristics of the receptive fields in the central retina are more homogeneous. This homogeneity would simplify the comparison of retinas from normal and mutant strains of the mouse.
Prenatal development of axon outgrowth and connectivity in the ferret visual system
Authors: Johnson J. Kelly , Casagrande V. A.
Published: June 2009

The objective of this study was to determine when the retina, lateral geniculate nucleus (LGN), and striate cortex first send out axons, and first connect with each other, during embryonic development in the ferret. Specifically, we were interested in the timing relationship between axon outgrowth and known temporal patterns of neurogenesis in the LGN and striate cortex. Ferrets (Mustela putorius furo) were selected for study because of their immature developmental state in late gestation and relatively large litters.

We examined axon outgrowth from the retina, and anlagen of presumptive LGN and striate cortex between embryonic day 21–30 (E21–E30) usingin situinoculations of two fluorescent lipophilic dyes, Dil and DiA. Dil inoculations were made into the cortex and contralateral thalamus, and DiA inoculations were made into the contralateral eye. Retinal axon termination zones in the diencephalon following the DiA inoculations were used to validate the location of the LGN.

Visual cortex and LGN neurogenesis begins at E20 in ferrets. No axon outgrowth could be documented from retina or anlagen of striate cortex and LGN until E24. At E24 some retinal axons reach and cross the chiasm, cortical axons extend some distance within the cortical radiations, and thalamic axons are within the internal capsule. Retinogeniculate, geniculocortical, and corticogeniculate axons extend to their target structures by E27, as evidenced by retrograde labeling in cells of origin.

These data suggest that in the ferret retina, and developing LGN and striate cortex, (1) axon outgrowth from each visual area begins within 24-h of each other, after neurogenesis has begun at the source but before it is complete in the target; (2) axons may be generated before parent cell bodies have completed migration; and (3) arriving axons are in a position to influence target structures almost from their inception.
Photopigments of dogs and foxes and their implications for canid vision
Authors: Jacobs Gerald H. , Deegan Jess F. , Crognale Michael A. , Fenwick John A.
Published: June 2009

Electroretinogram (ERG) flicker photometry was used to examine the photopigment complements of representatives of four genera of Canid: domestic dog (Canis familiaris), Island gray fox (Urocyon littoralis), red fox (Vulpes vulpes), and Arctic fox (Alopex lagopus).These four genera share a common cone pigment complement; each has one cone pigment with peak sensitivity of about 555 nm and a second cone pigment with peak at 430–435 nm. These pigment measurements accord well with the conclusions of an earlier investigation of color vision in the dog, and this fact allows some predictions about color vision in the wild canids. An additional set of measurements place the peak of the dog rod pigment at about 508 nm.
Effects of vasoactive intestinal peptide on ganglion cells in the rabbit retina
Authors: Jensen Ralph J.
Published: June 2009

The effects of vasoactive intestinal peptide (VIP) on the extracellularly recorded activity of ganglion cells were studied in superfused rabbit retinas. VIP, applied to the bathing solution, significantly increased the maintained activity of both OFF-center and ON-center brisk ganglion cells. The transient, excitatory responses of these cells to flashes of light (spots or annuli centered over the receptive field) were either unaffected or moderately reduced. VIP did not affect the responses of most ON/OFF directionally selective ganglion cells to a moving light stimulus. Furthermore, maintained activity of most of these cells remained absent.

Effects of VIP on the light responses of ganglion cells were pronounced in retinas that were bathed with the dopamine D1antagonist (+)-SCH 23390. For OFF-center brisk ganglion cells, VIP brought out both the center and surround excitatory responses that were selectively reduced by (+)-SCH 23390. Similarly, VIP brought out the leading edge responses that were reduced by (+)-SCH 23390 in ON/OFF directionally selective ganglion cells to a moving light stimulus. VIP did not however reverse the effects of (+)-SCH 23390 on ON-center brisk ganglion cells. It is argued that VIP counteracts the effects of (+)-SCH 23390 on OFF-center brisk ganglion cells and ON/OFF directionally selective ganglion cells by stimulating adenylate cyclase activity in dopamine-receptive cells of the retina.
Effects of monocular enucleation, tetrodotoxin, and lid suture on cytochrome-oxidase reactivity in supragranular puffs of adult macaque striate cortex
Authors: Trusk Thomas C. , Kaboord Wayne S. , Wong-Riley Margaret T.T.
Published: June 2009

The laminar structure and cellular distribution of cytochrome-oxidase (CO) reactivity in supragranular puffs of striate cortex was examined in adult macaque monkeys surviving various periods of monocular enucleation, lid suture, and retinal impulse blockage with tetrodotoxin (TTX). Enucleation and TTX produced a rapid and severe loss in the size of the CO reactive region in puffs dominated by the removed or treated eye compared to slower and less marked reductions obtained in deprived puffs of lid-sutured monkeys. In all deprived animals, the cross-sectional areas of deprived puffs decreased most rapidly in the upper layers (2 and 3A). In long-term enucleated (60 wks) and TTX-treated (4 wks) monkeys, puff area was severely reduced in layer 3B, while reactivity in layer 3B appeared partially spared in lid-sutured monkeys. The density of the CO reaction product was significantly and evenly reduced throughout deprived puffs for all of the monkeys examined; however, this decrease was less severe in adult monkeys lid-sutured for 11 wks. Although no evidence for cell loss was obtained, all three forms of visual deprivation led to lower counts of neuronal perikarya with high levels of CO reaction product in both deprived puff and interpuff areas. This effect was less marked in the deprived puffs of monkeys lid-sutured for 2.5 and 3 yrs, suggesting recovery of CO activity in some neurons. Neurons in deprived puffs and interpuffs were generally similar in size to those in nondeprived regions, although CO-reactive cells were significantly smaller in the deprived puffs of monkeys enucleated for 28.5 or 60 wks. These results indicate that the metabolic response of neuronal elements in supragranular striate cortex depends upon the nature of the visual deficit. The partial sparing of CO reactivity in deprived puffs of lid-sutured monkeys may reflect the continued transmission of certain types of visual stimuli through a closed eyelid.
Immunohistochemical localization of GABAAreceptors in the retina of the new world primateSaimiri sciureus
Authors: Hughes Thomas E. , Carey Russell G. , Vitorica Javier , de Blas Angel L. , Karten Harvey J.
Published: June 2009

A large population of amacrine cells in the retina are thought to use GABA as an inhibitory neurotransmitter in their synaptic interactions within the inner plexiform layer. However, little is known about their synaptic targets; the neurons that express the receptors for GABA have not been clearly identified. Recently, the GABAAreceptor has been isolated and antibodies have been raised against it. These antibodies have proven useful for the immunocytochemical localization of the receptor, and two brief reports describing the distribution of GABAAreceptor immunoreactivity in the retina have appeared (Richards et al., 1987; Mariani et al., 1987). We used a monoclonal antibody (62–3G1) against the GABAAreceptor to study the retina of the New World primateSaimiri sciureus.

Labeled somata were found in the inner nuclear layer (INL) and ganglion cell layer (GCL). The staining was confined to what appeared to be the cell's plasmalemma and small cytoplasmic granules. Most of the labeled neurons in the INL had small somata (5–7 μm in diameter) located at the vitreal edge of the layer. They arborized in two laminae (approximately 2 and 4) of inner plexiform layer (IPL). Ventral to the optic disc (2.5 mm) they comprised 29% of the cells present. A few of the labeled neurons appeared to be interplexiform cells or flat bipolar cells, with labeled processes that extended into both the IPL and the inner half of the outer plexiform layer. In the GCL, the labeled somata were among the largest present (13–20 μm in diameter), and 2.5 mm ventral to the optic disc they made up 15% of the cells present. Experiments in which immunoreactive somata were retrogradely labeled following the injection of fluorescent tracers into the optic tract provided a conclusive demonstration that some of the immunoreactive somata were ganglion cells. The antibody often labeled their axons in the optic fiber layer. This suggests that the GABAAreceptors are transported anterogradely to the retinal terminal fields. The dendrites of the immunoreactive ganglion cells extended into the 2 laminae of labeled processes in the IPL, and their primary dendritic arbors were, at any given eccentricity, quite similar in appearance. This homogeneity suggests that they comprise a particular subset of the ganglion cells.

Sections simultaneously labeled with the monoclonal antibody against the GABAAreceptor and antisera against either L-glutamic acid decarboxylase (GAD) or GABA revealed that the GAD/GABA was distributed much more widely in the IPL than the GABAAreceptor. This variance may reflect either the presence of other, perhaps GABAB, receptors in the IPL or GABA in portions of the IPL where it is ineffective as a neurotransmitter.
Organotypic slice culture of the mammalian retina
Authors: Feigenspan Andreas , Bormann Joachim , Wässle Heinz
Published: June 2009

Vertical slices of 6-day postnatal (P6) rat retina were cut at a thickness of 100 μm and cultured using the roller-tube technique. After 14–21 daysin vitrothere was significant distortion of normal retinal architecture, but localized areas of the slices showed the typical pattern of layering of mature retina. The following immunocytochemical markers were used to characterize the different retinal cell types: antibodies against protein kinase C (PKC), calcium binding protein (CabP 28kD), neurofilaments (NF), glia-specific antibodies (GFAP, vimentin), and transmitter-specific antibodies (GABA, TH). The expression of these markers was compared in P6 retina, adult retina, and slice culture. To further characterize the cultured cells, patch-clamp recordings were performed in combination with intracellular injection of Lucifer Yellow (LY). Transmitter-and voltage-gated membrane currents were recorded from morphologically identified neurons. The experiments show that a mammalian slice culture can be used to study differentiation and function of retinal cell types.
The histaminergic innervation of the lateral geniculate complex in the cat
Authors: Uhlrich Daniel J. , Manning Karen A. , Pienkowski Thomas P.
Published: June 2009

The histaminergic innervation of the thalamic dorsal and ventral lateral geniculate nuclei and the perigeniculate nucleus of the cat was examined immunohistochemically by means of an antibody to histamine.

We find histamine-immunoreactive neurons in the cat brain are concentrated in the ventrolateral portion of the posterior hypothalamus, confirming a previous report. However, this cell group also spreads into medial, dorsal, and extreme lateral regions of the posterior hypothalamus and extends as far rostral as the optic chiasm.

Histamine-labeled fibers cover all regions of the lateral geniculate complex, but the density of labeling varies. The ventral lateral geniculate nucleus (vLGN) is most densely labeled, the A laminae of the dorsal lateral geniculate are sparsely labeled, and the geniculate C laminae and the perigeniculate nucleus show intermediate amounts of label. Thus, histaminergic fibers demonstrate a predilection for zones innervated by the W-cell system. Labeled fibers exhibit few branchings and numerousen passantswellings, lending a beaded appearance. The vLGN showed more instances of fibers with larger-sized swellings (up to 2 μm).

Following injections of biotinylated tracers into the hypothalamus, we find labeled fibers throughout the lateral geniculate complex. The anterogradely labeled fibers resemblethe histaminergic fibers in morphology, distribution, and relative bouton size. Thus, the hypothalamus appears to be the source of the histaminergic fibers in the lateral geniculate complex.

Histamine-labeled fibers in the dorsal lateral geniculate nucleus (dLGN) exhibit uncommon ultrastructural morphology. Many extremely large, round, or elliptical vesicles fill the fiber swellings. Swellings are directly apposed to a variety of other dendritic and axonal profiles, but thus far no convincing synaptic contacts have been seen. The distribution and appearance of these histaminergic fibers resembles those reported for serotonergic fibers.

Our results support the idea that histamine works nonsynaptically as a neuromodulator in the lateral geniculate complex, affecting the level of visual arousal.
Selective depletion of beta cells affects the development of alpha cells in cat retina
Authors: Ault Steven J. , Thompson Kirk G. , Zhou Yifeng , Leventhal Audie G.
Published: June 2009

The results of previous studies suggest that class-specific interactions contribute to the development of the different classes of retinal ganglion cells. We tested this hypothesis by examining the morphologies and distributions of alpha (α) cells in regions of mature cat retina selectively depleted of beta (β) cells as a result of visual cortex lesions at birth. We find that α cells in regions of central retina depleted of β cells are abnormally large while α cells in regions of peripheral retina depleted of β cells are abnormally small. The normal central-to-peripheral α cell soma-size gradient is absent in hemiretinae depleted of β cells. The dendritic fields of α cells in the border of β-cell-depleted hemiretina extend preferentially into the β-cell-poor hemiretina. In spite of this, α cell bodies retain their normal retinal distribution and remain distributed in a nonrandom mosaic-like pattern. Thus, it appears that the development of α retinal ganglion cells is influenced by interactions both with other α cells (class-specific interactions) and with surrounding β cells (nonclass-specific interactions).
Brain stem and cortical contributions to the generation of horizontal optokinetic eye movements in humans
Authors: Harris Laurence R. , Lewis Terri L. , Maurer Daphne
Published: June 2009

We evaluated the subcortical pathways’ contribution to human adults’ horizontal OKN by using a method similar to that used previously with cats (Harris & Smith, 1990; Smith & Harris, 1991). Five normal adults viewed plaids composed of two drifting sinusoidal gratings arranged such that their individual directions of drift were 60 deg or more from the direction of coherent motion of the overall pattern. Physiological evidence indicates that under monocular viewing, nasalward coherent motion gives advantage to any crossed subcortical contribution while temporalward coherent motion minimizes it. We recorded horizontal eye movement by infrared reflection and asked subjects to report the perceived direction of motion.

During both binocular and monocular viewing, the direction of the slow phase of OKN fell closer to the direction of coherent movement than to that of the oriented components. Monocular viewing produced no nasal-temporal asymmetries in the influence of coherent motion on the direction of OKN. This suggests that in humans the influence of coherent motion is mediated primarily by cortical mechanisms and, unlike in cats, with little or no involvement of subcortical mechanisms in the generation of horizontal OKN.
A second episode of ganglion cell death takes place when an optic nerve regenerates for a second time in the frog
Authors: Beazley L. D. , Darby J.E.
Published: June 2009

We have previously reported that during optic nerve regeneration in the frog, 30–40% of retinal ganglion cells die, the loss being complete within 10 weeks. In the present study, we crushed the optic nerve, waited 10 weeks, and then recrushed the nerve at the same site. Retinae were examined 10 weeks later. We estimated ganglion cell numbers from cresyl-violet-stained wholemounts and found a fall of 53% compared to normals. The loss was significantly greater than the losses of 36% and 35%, respectively, in frogs which received a single optic nerve crush and were examined 10 or 20–24 weeks later. The results indicate that a second episode of ganglion cell death took place when the optic nerve regenerated a second time. We conclude that ganglion cells in the frog are not comprised of two subpopulations, only one of which intrinsically possesses the ability to regenerate.
The segregation of ON- and OFF-center responses in the lateral geniculate nucleus of normal and monocularly enucleated ferrets
Authors: Morgan James , Thompson Ian D.
Published: June 2009

We have investigated the distribution of ON- and OFF-center responses in the lateral geniculate nucleus of ferrets with normal and abnormal retinal projections. Electrophysiological recordings in normal pigmented animals confirm previous studies on mustelids showing that ON-center responses are found in the anterior, inner parts of laminaeAandAIand OFF-center responses in posterior, outer leaflets. In albino animals, laminaAdisplays normal patterns of ON/OFF segregation but in laminaAI, which receives an abnormal crossed retinal projection, no consistent patterns of segregation are found. Following monocular enucleation on the day of birth, the uncrossed projection in pigmented ferrets remains expanded across the LGN. Anatomically and physiologically, this projection is segregated into two leaflets: an anterior, inner ON-center leaflet and a posterior outer OFF-center leaflet. We conclude that the persistence of ON/OFF segregation, independent of geniculate location, suggests that self-sorting of retinal input is an important factor in generating the segregation.
Dendritic competition in the developing retina: Ganglion cell density gradients and laterally displaced dendrites
Authors: Linden Rafael
Published: June 2009

Dendrites of retinal ganglion cells (RGCs) tend to be distributed preferentially toward areas of reduced RGC density. This, however, does not occur in the retina of normal pigmented rats, in which it has been suggested that the centro-peripheral gradient of RGC density is too shallow to provide directional guidance to growing dendrites. In this study, laterally displaced dendrites of RGCs retrogradely labeled with horseradish peroxidase were related to cell density gradients induced experimentally in the rat retina. Neonatal unilateral lesions of the optic tract produced retrograde degeneration of contralaterally projecting RGCs, but spared ipsilaterally projecting neurons in the same retina. These lesions created an anomalous temporal to nasal gradient of cell density across the decussation line, opposite to the nasal to temporal gradient found along the same axis in either normal rats or rats that had the contralateral eye removed at birth. RGCs in rats that received optic tract lesions had their dendrites displaced laterally toward the depleted nasal retina, while in either normal or enucleated rats there was no naso-temporal asymmetry. The lateral displacement affected both primary dendrites and higher-order branches. However, the gradient of cell density after optic tract lesions was less steep than the gradient in either normal or enucleated rats. To test for the presence of steeper gradients at early stages of development, RGC density gradients were also examined at postnatal day 5 (P5). In normal rats, the RGCs were homogeneously distributed throughout the retina, while rats given optic tract lesions at birth already showed a temporo-nasal density gradient at P5. Still, this anomalous gradient was less steep than that found in normal adults. It is concluded that the time course, rather than the steepness of the RGC density gradient, is the major determinant of the lateral displacement of dendritic arbors with respect to the soma in developing RGCs. The data are consistent with the idea that the overall shape of dendritic arbors depends in part on dendritic competition during retinal development.
Whole-cell currents activated at nicotinic acetylcholine receptors on ganglion cells isolated from goldfish retina
Authors: Yazejian Bruce , Fain Gordon L.
Published: June 2009

We have recorded whole-cell membrane currents in response to exogenously applied acetylcholine (ACh), nicotine, and 1,1 dimethyl-4-phenyl piperazinium iodide on retinal ganglion cells enzymatically dissociated from goldfish retina. Agonist applications induced nicotinic-type responses in a majority of cells when cells were isolated under optimal conditions. Currents were reminiscent of nicotinic-type ganglionic responses. Dose-response measurements of ACh-induced currents indicated an EC50 of 52 μM and a Hill coefficient of 0.6. Currents were selective for Na+ over Cl− and were highly inwardly rectifying. Responses were blocked reversibly by d-tubocurarine, hexamethonium chloride, and N-methyl-D-glucamine. In 50% of the cases, α-bungarotoxin reversibly blocked the current induced by ACh application. The blocking action of mecamylamine was irreversible and independent of the presence of agonist but was more effective in the presence of ACh. We conclude that functional nicotinic ACh receptors exist on most goldfish retinal ganglion cells.
Topography of supplementary eye field afferents to frontal eye field in macaque: Implications for mapping between saccade coordinate systems
Authors: Schall Jeffrey D. , Morel Anne , Kaas Jon H.
Published: June 2009

Two discrete areas in frontal cortex are involved in generating saccadic eye movements—the frontal eye field (FEF) and the supplementary eye field (SEF). Whereas FEF represents saccades in a topographic retinotopic map, recent evidence indicates that saccades may be represented craniotopically in SEF. To further investigate the relationship between these areas, the topographic organization of afferents to FEF from SEF in Macaco mulatto was examined by placing injections of distinct retrograde tracers into different parts of FEF that represented saccades of different amplitudes. Central FEF (lateral area 8A), which represents saccades of intermediate amplitudes, received afferents from a larger portion of SEF than did lateral FEF (area 45), which represents shorter saccades, or medial FEF (medial area 8A), which represents the longest saccades in addition to pinna movements. Moreover, in every case the zone in SEF that innervated lateral FEF (area 45) also projected to medial FEF (area 8A). In one case, a zone in rostral SEF projected to both lateral area 8A from which eye movements were evoked by microstimulation as well as medial area 8A from which pinna movements were elicited by microstimulation. This pattern of afferent convergence and divergence from SEF onto the retinotopic saccade map in FEF is indicative of some sort of map transformation between SEF and FEF. Such a transformation would be necessary to interconnect a topographic craniotopic saccade representation in SEF with a topographic retinotopic saccade representation in FEF.
Characterization of a calcium/calmodulin-dependent protein phosphatase in theLimulusnervous tissue and its light regulation in the lateral eye
Authors: Ellis D. Z. , Edwards S. C.
Published: June 2009

Calcium (Ca2+) plays an integral role in the light response of the photoreceptors in both vertebrate and invertebrate organisms. In the ventral eye of the horseshoe crab,Limulus polyphemus, a flash of light delivered to a dark-adapted photoreceptor stimulates a rapid rise in intracellular free calcium concentration ([Ca2+]i), which in turn mediates light adaptation. It has previously been demonstrated that inLimulusphotoreceptors light,viaCa2+, activate s a calcium/calmodulin (Ca2+/CaM)-dependent protein kinase which increases the phosphorylation of arrestin. We now have identifie d biochemically, a calcium/calmodulin-dependent protein phosphatase (Ca2+/CaM PP ) in homogenates of theLimuluslateral and ventral eye, brain, and lateral optic nerve using as a substrate, a32P-labeled peptide fragment of the regulatory subunit of cAMP-dependent protein kinase (RII). This protein phosphatase shares biochemical properties with calcineurin, a Ca2+/CaM-dependent protein phosphatase (type-2B). Its activity is enhanced by Ca2+, calmodulin and Mn2+; and is inhibited by mastoparan, a calmodulin antagonist, and a synthetic peptide corresponding to the autoinhibitory domain of mammalian calcineurin. Most importantly, light regulates the Ca2+/CaM PP activity in the lateral eye. While there is no difference in basal activity in long-term dark- or light-adapted preparations, Ca2+enhances Ca2+/CaM PP activity only in long-term light-adapted eyes.
Vasoactive intestinal polypeptide modulates GABAAreceptor function through activation of cyclic AMP
Authors: Veruki Margaret L. , Yeh Hermes H.
Published: June 2009

Vasoactive intestinal polypeptide (VIP) has been shown to potentiate current responses elicited by activation of the GABAAreceptor (IGABA) in freshly dissociated ganglion cells of the rat retina. Here we tested the hypothesis that this heteroreceptor cross talk is mediated by an intracellular cascade of events that includes the sequential activation of a stimulatory guanine nucleotide binding (Gs) protein and adenylate cyclase, the subsequent increase in levels of cyclic AMP and, finally, the action of the cyclic AMP-dependent protein kinase (PKA). Intracellular dialysis of freshly dissociated ganglion cells with GTPγsirreversibly potentiatedIGABA, while GDPßseither decreased or had no effect onIGABA. Additionally, GDPßsblocked the potentiation ofIGABAby VIP. Cholera toxin rendered VIP ineffective in potentiatingIGABA, while pertussis toxin had no effect on the VIP-induced potentiation ofIGABA. Extracellular application of either forskolin or 8-bromo-cyclic AMP potentiatedIGABA, as did the introduction of cyclic AMP directly into the intracellular compartment through the recording pipet. Intracellular application of cyclic AMP-dependent protein kinase (PKA) potentiatedIGABA, while a PKA inhibitor blocked the potentiating effect of VIP. These results lead us to conclude that activation of a cyclic AMP-dependent second-messenger system mediates the modulation of GABAAreceptor function by VIP in retinal ganglion cells.
Regulation of endogenous dopamine release in amphibian retina by melatonin: The role of GABA
Authors: Boatright Jeffrey H. , Rubim Nara M. , Iuvone P. Michael
Published: June 2009

In the retina of the African clawed frog (Xenopus laevis), endogenous dopamine release increases in light and decreases in darkness. Exogenous melatonin and several chemical analogs of melatonin suppressed light-evoked dopamine release from frog retina in a concentration-dependent manner. The rank order of potency for inhibition of light-evoked dopamine release was melatonin » 5-methoxytryptamine ≥N-acetylserotonin > 5-methoxytryptophol ⋙ serotonin. Melatonin did not suppress dopamine release below levels seen in darkness. The putative melatonin receptor antagonist luzindole inhibited the effect of melatonin. Luzindole enhanced dopamine release in darkness but had little effect in light. These data suggest a role for endogenous melatonin in dark-induced suppression of retinal dopamine.

Picrotoxin and bicuculline, GABA-A receptor antagonists, blocked melatonin-induced suppression of dopamine release. In the presence of melatonin, bicuculline was significantly less potent in stimulating dopamine release. These results suggest that melatonin enhances GABAergic inhibition of light-evoked dopamine release. This mechanism may underlie the light/dark difference in dopamine release in vertebrate retina.
Cholinoceptive neurons in the retina of the chick: an immunohistochemical study of the nicotinic acetylcholine receptors
Authors: Keyser K.T. , Hughes T.E. , Whiting P.J. , Lindstrom J.M. , Karten H.J.
Published: June 2009

Monoclonal antibodies directed against nicotinic acetylcholine receptors (nAChRs) were used to identify and characterize cholinoceptive neurons in the chick retina. Two monoclonal antibodies (mAbs), mAb 210 and mAb 270, stained many neurons in both the inner nuclear layer (INL) and ganglion cell layer (GCL). A class of large labeled cells in the inner INL were positioned at the INL/IPL (inner plexiform layer) border and resembled displaced ganglion cells (DGCs). Their identity was confirmed with injections of rhodamine-labeled microspheres into the ventral tectum and nucleus of the basal optic root (nBOR). Four days after the injection, large nAChR-positive neurons in the inner INL were labeled with beads. The distribution of these cells matched that reported for DGCs in the chicken and pigeon (Reiner et al., 1979; Fite et al., 1981). Many smaller cells in the INL also exhibited nAChR immunoreactivity. These cells were not retrogradely labeled after bead injections into retinal recipient areas. Their processes entered the IPL where they arborized in a band comprised of the inner leaflet of lamina 1 and all of lamina 2. In some instances, a process continued inward to lamina 4. These neurons were tentatively identified as amacrine cells because of their position and branching pattern.

Approximately 12–18% of the cells in the GCL exhibited nAChR immunoreactivity. Many of these cells could be classified as ganglion cells as their axons were also labeled following exposure to nAChR antibodies. Their distribution mirrored that of all ganglion cells with a higher density of cells in the central retina than in the periphery (Ehrlich, 1981). A “double label” technique was used to compare the distribution of nAChR-positive neurons with that of the choline acetyltransferase-positive (ChAT), cholinergic neurons in the chick retina. The two antigens were visualized with two different fluorophores: FITC and RITC. We were unable to find any cells in either the INL or GCL that exhibited both ChAT- and nAChR-like immunoreactivity. The nAChR-positive cells and the ChAT-positive cells both arborized in two bands within the IPL. The patterns were in perfect register in the inner IPL (lamina 4). But, in the outer IPL, the nAChR-positive dendrites were observed in the inner leaflet of lamina 1 and in all of lamina 2 while the ChAT-positive dendrites did not extend into the innermost portion of lamina 2.
Effects of serial lesions of telencephalic components of the visual system in pigeons
Authors: Riley Nell M. , Hodos William , Pasternak Tatiana
Published: June 2009

A serial-lesion technique was used to investigate interactions in visual processing between telencephalic components of the pigeon visual system. Pigeons were trained to discriminate pairs of stimuli that differed in color, intensity or pattern. After mastering the discrimination tasks, they were assigned to one of three groups. The first group (WI-EII) received lesions of the visual Wulst and were retested. After the discrimination tasks were again mastered, a second set of lesions was made, this time in the ectostriatum. The birds were tested once again after the second surgery. The second group (EI-WII), underwent the same sequence of events except that the order of the lesions was reversed. In the third group (E + W), lesions of both the visual Wulst and ectostriatum were made in a single operation, followed by retesting. The performance after the first lesion of the subjects in each of the two-stage lesion groups was typical of performance after such lesions; i.e. the birds with visual-Wulst lesions showed little or no impairment on any of the tasks, whereas the pigeons with ectostriatum lesions showed considerable deficits in intensity and pattern discrimination, which diminished after prolonged retraining. In contrast, the pigeons in the one-stage group (E + W) showed profound deficits that appeared to be permanent. The performance after the second operation of the WI-EII group was the same as that of pigeons with lesions of ectostriatum alone; i.e. destruction of ectostriatum first or second resulted in the same duration of impairment. The performance of the EI-WII group after its visual Wulst lesion, however, was similar to that observed in the E + W group. The results are interpreted as a reflection of parallel processing within the avian visual system; i.e. the presence of an intact tectofugal pathway may mask the effects of thalamofugal pathway interruption.