bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of directional expectations on motion perception
and pursuit eye movements
Authors: KRAUZLIS RICHARD J. , ADLER SCOTT A.
Published: December 2002

Expectations about future motions can influence both perceptual
judgements and pursuit eye movements. However, it is not known
whether these two effects are due to shared processing, or to
separate mechanisms with similar properties. We have addressed
this question by providing subjects with prior information about
the likely direction of motion in an upcoming random-dot motion
display and measuring both the perceptual judgements and pursuit
eye movements elicited by the stimulus. We quantified the
subjects' responses by computing oculometric curves from
their pursuit eye movements and psychometric curves from their
perceptual decisions. Our results show that directional cues
caused similar shifts in both the oculometric and psychometric
curves toward the expected motion direction, with little change
in the shapes of the curves. Prior information therefore biased
the outcome of both eye movement and perceptual decisions without
systematically changing their thresholds. We also found that
eye movement and perceptual decisions tended to be the same
on a trial-by-trial basis, at a higher frequency than would
be expected by chance. Furthermore, the effects of prior
information were evident during pursuit initiation, as well
as during pursuit maintenance, indicating that prior information
likely influenced the early processing of visual motion. We
conclude that, in our experiments, expectations caused similar
effects on both pursuit and perception by altering the activity
of visual motion detectors that are read out by both the oculomotor
and perceptual systems. Applying cognitive factors such as
expectations at relatively early stages of visual processing
could act to coordinate the metrics of eye movements with
perceptual judgements.
Facilitation and suppression of single striate-cell activity
by spatially discrete pattern stimuli presented beyond the
receptive field
Authors: MIZOBE KEIKO , POLAT URI , PETTET MARK W. , KASAMATSU TAKUJI
Published: December 2002

Visual stimulation of a region outside the receptive field
of single cells in visual cortex often results in the modulation
of their responses. The modulatory effects are thought to be
mediated through lateral connections within visual cortex. Research
on lateral interactions commonly shows suppression. There has
been no systematic study of the optimal conditions for
facilitation. Here we have studied the nature of the modulation
using a new type of compound stimulus: contrast reversal of
pattern stimuli made of three discrete grating patches. The
middle patch, optimally fitted to the receptive field in
orientation, size, and spatial as well as temporal frequencies,
was flanked by two similar patches presented well outside the
receptive field. We found that (1) both facilitation and
suppression occurred often in the same cells, when orientations
of the target and flankers matched the receptive-field's
optimal orientation; (2) facilitation with collinear flankers
occurred most frequently at target contrasts just above the
cell's firing threshold and suppression prevailed at high
contrasts; (3) facilitative or suppressive modulation was obtained
with target-flankers separation of up to 12 deg or more; (4)
collinear facilitation was lost when flankers' orientation
was rotated by 90 deg, while keeping all other parameters the
same; and (5) neither the modulation mode nor the proportion
of modulated cells was related to the cell types (simple
vs. complex cells) and cells' laminar locations.
Here we have provided physiological evidence for
contrast-dependent, collinear facilitation probably
underlying perceptual grouping in humans.
Salamander UV cone pigment: Sequence, expression, and spectral
properties
Authors: MA JIAN-XING , KONO MASAHIRO , XU LIN , DAS JOYDIP , RYAN JAMES C. , HAZARD E. STARR , OPRIAN DANIEL D. , CROUCH ROSALIE K.
Published: December 2002

The visual pigment from the ultraviolet (UV) cone photoreceptor
of the tiger salamander has been cloned, expressed, and
characterized. The cDNA contains a full-length open reading
frame encoding 347 amino acids. The phylogenetic analysis indicates
that the highest sequence homology is to the visual pigments
in the S group. The UV opsin was tagged at the carboxy-terminus
with the sequence for the 1D4 epitope. This fusion opsin was
expressed in COS-1 cells, regenerated with 11-cis retinal
(A1) and immuno-purified, yielding a pigment with an absorbance
maximum (λmax) of 356 nm which is blue shifted
from the absorption of retinal itself. The transducin activation
assay demonstrated that this pigment is able to activate rod
transducin in a light-dependent manner. Regeneration with
11-cis 3,4-dehydroretinal (A2) yielded a pigment with
a λmax of 360 nm, only 4 nm red shifted from
that of the A1 pigment, while bovine rhodopsin generated
with A2 showed a 16-nm red shift from the corresponding A1 pigment.
These results demonstrate that the trend for a shorter wavelength
pigment to have a smaller shift of λmax between
the A1 and A2 pigments also fits UV pigments. We hypothesize
that the small red shift with A2 could be due to a twist in
the chromophore that essentially isolates the ring double bond(s)
from conjugation with the rest of the polyene chain.
Human neural responses elicited to observing the actions of others
Authors: WHEATON KYLIE J. , PIPINGAS ANDREW , SILBERSTEIN RICHARD B. , PUCE AINA
Published: December 2002

Monkey electrophysiological and human neuroimaging studies
indicate the existence of specialized neural systems for the
perception and execution of actions. To date, the dynamics of
these neural systems in humans have not been well studied. Here,
we investigated the spatial and temporal behavior of human neural
responses elicited to viewing motion of the face, hand, and
body. Scalp event-related potentials (ERPs) were recorded in
20 participants viewing videotaped mouth (opening, closing),
hand (closing, opening), and body stepping (forward, backward)
movements. ERP peak differences within the movements of each
body part were compared using topographical maps of voltage,
voltage difference, and Student's t-test at ERP
peak latencies. Predominantly temporoparietal negative ERPs
occurred to motion of all body parts within 200 ms postmovement
onset. Hand closure elicited a significantly greater negativity
than opening, particularly in the left hemisphere. Vertex positive
ERPs within 300 ms postmovement onset were elicited to hand
and body motion. A significantly greater positivity occurred
for the body stepping forward relative to stepping backward.
The ERP topography was consistent with observed activation foci
in human neuroimaging studies. Our data indicate that the neural
activity of a system dedicated to the perception of high-level
motion stimuli can rapidly differentiate between movements across
and within body parts.
Ocular dominance columns in the adult New World Monkey
Callithrix jacchus
Authors: CHAPPERT-PIQUEMAL CATHERINE , FONTA CAROLINE , MALECAZE FRANÇOIS , IMBERT MICHEL
Published: December 2002

In the marmoset Callithrix jacchus, ocular dominance
columns (ODC) have been reported to be present in young animals,
but absent in adults (Spatz, 1989). We have studied in juvenile
and adult animals the postnatal organization of the
retino-geniculo-cortical afferents by means of transneuronal
labeling. We show in the present work that ODC are present in
the primary visual cortex of Callithrix jacchus, both
in the adult and in the juvenile animal. The present work confirms
the presence of ODC in the visual cortex of juvenile marmoset
before the end of the first postnatal month. In 2-month-old
animals, ODC are well demarcated in IVcα and IVcβ. In
the adult marmosets, the present data clearly show that the
primary visual cortex is also organized with ODC. In horizontal
sections, they form a mosaic through the ventral and dorsal
calcarine cortex and through the dorso-lateral occipital part
of the striate cortex. In frontal sections, their presence is
manifest in IVcβ within the calcarine cortex and they only
faintly appear in IVcα. These new findings are important
since they underline the usefulness of the adult New World Monkeys
as a model in visual research.
Localization of amino acid neurotransmitters following in
vitro ischemia and anoxia in the rat retina
Authors: NAPPER GENEVIEVE A. , PIANTA MICHAEL J. , KALLONIATIS MICHAEL
Published: December 2002

Glutamate and γ-aminobutyric acid (GABA) are two of the
dominant neurotransmitters in the retina and brain. The
production/degradation of glutamate and GABA involves an intricate
interrelationship between neurons and glia, as well as aerobic
and anaerobic metabolic pathways. The aim of this work was to
develop an in vitro model of retinal ischemia/anoxia
and determine the changes in cellular localization of glutamate
and GABA and the time course for such changes. After
anoxic/ischemic insult, glutamate and GABA rapidly accumulate
within glia with GABA showing a quicker time course and larger
magnitude change. The accumulation time constant for both glutamate
and GABA under anoxic conditions was dependent upon glucose
concentration: high glucose levels resulted in delayed glial
amino acid loading. The differences in time constants between
GABA and glutamate glial loading most likely reflect the multitude
of glutamate degradation pathways compared to the single
aerobically dependent GABA pathway. Oxygen availability and
reduced glucose (hypoglycemia) lead to an almost immediate increase
(within 1 min) of glutamate and GABA labelling within glia.
In addition, altered labelling patterns were found under
anoxic/ischemic conditions for amino acids involved in glutamate
transamination reactions: aspartate, leucine, alanine, and
ornithine. These changes are consistent with alterations of
equilibria of enzymatic reactions involved in glutamate metabolism,
and thus support a role for all four amino acids in glutamate
metabolism within a variety of retinal neurons.
Heat shock protein 90 in retinal ganglion cells: Association
with axonally transported proteins
Authors: BERNSTEIN STEVEN L. , RUSSELL PAUL , WONG PAUL , FISHELEVICH RITA , SMITH LOIS E.H.
Published: December 2002

The mRNAs for heat shock protein 90 (HSP90) are found at highest
levels (differentially expressed) in the primate retinal fovea,
the region of highest visual acuity, compared to the peripheral
retina. HSP90 expression and retinal associations were analyzed
by immuno-localization, in situ hybridization, and
western analysis. Retinal ganglion cells (RGCs) express much
of the HSP90 mRNA present in the primate retinal fovea. A large
fraction of RGC synthesized HSP90 is apparently present in the
axonal compartment. To identify the role of HSP90 protein in
the optic nerve and retina, co-immunoprecipitation experiments
were performed, using antibodies specific for HSP90 isoforms.
The immunoprecipitates were analyzed for neurotrophin receptor
and ligand activities, and MAP kinase activity. MAP kinase assay
was used to determine the activation state of MAP kinase associated
with HSP90. HSP90 proteins selectively associate with the inactive
form of full-length tyrosine kinase growth factor receptor trkB,
suggesting utilization during anterograde axonal transport.
Activated MAP kinase, associated with the trk downstream signaling
cascade, was found to co-immunoprecipitate with optic nerve
HSP90, suggesting that HSP90 may be utilized in retrograde
transport of the secondary messengers associated with neurotrophin
signaling. HSP90 can thus be hypothesized to play a role in
bidirectional RGC axonal protein transport.
Comparative structural and functional analysis of photoreceptor
neurons of Rho-/- mice reveal increased survival on
C57BL/6J in comparison to 129Sv genetic background
Authors: HUMPHRIES MARIAN M. , KIANG SOPHIE , McNALLY NIAMH , DONOVAN MARY ANNE , SIEVING PAUL A. , BUSH RONALD A. , MACHIDA SHIGEKI , COTTER THOMAS , HOBSON AUDREY , FARRAR JANE , HUMPHRIES PETE , KENNA PAUL
Published: December 2002

To explore the possible influence of defined genetic backgrounds
on photoreceptor viability and function in mice carrying a targeted
disruption of the rhodopsin gene, the severities of retinopathies
in Rho-/- mice on C57BL/6J and 129Sv congenic backgrounds
were compared by light microscopy and electroretinography and
qualitatively by in situ end labeling of DNA in apoptotic
photoreceptor nuclei of retinal sections. Cone photoreceptor
viability and function were shown to deteriorate more slowly
on the C57BL/6J background in comparison to that of the 129Sv,
with significantly greater numbers of outer nuclear layer nuclei
in the retinas of C57BL/6J mice at 3 and 4 months of age. Both
amplitude and waveform features of the ERG were shown to be
remarkably different in the two strains, indicating an
approximately 6-fold difference in C57BL/6J Rho-/-
mice compared to 129Sv Rho-/- mice at 80 days. Thus,
in comparison with the 129Sv strain, genetic modifiers appear
to constitute a component of the C57BL/6J background, the
expression of which significantly protects cone photoreceptors
from apoptotic death in a mutation-induced murine retinopathy.
The differences in phenotype revealed in this study are sufficient
in principle to provide a basis for comparisons to be made between
QTLs in light-induced and mutation-induced systems.
Characterization of the rod photoresponse isolated from the
dark-adapted primate ERG
Authors: JAMISON J.A. , BUSH R.A. , LEI B. , SIEVING P.A.
Published: December 2002

The a-wave of the human dark-adapted ERG is thought
to derive from activity of rod photoreceptors. However, other
sources within the retina could potentially perturb this simple
equation. We investigated the extent to which the short-latency
dark-adapted rod a-wave of the primate ERG is dominated
by the rod photoresponse and the applicability of the
phototransduction model to fit the rod a-wave.
Dark-adapted Ganzfeld ERGs were elicited over a 5-log-unit
intensity range using short bright xenon flashes, and the
light-adapted cone responses were subtracted to isolate the
rod ERG a-wave. Intravitreal 4-phosphono-butyric acid
(APB) and cis-2,3-piperidine-dicarboxylic acid (PDA) were applied
to isolate the photoreceptor response. The Hood and Birch version
of the phototransduction model, Rmax[1 −
e−I·S·(t−teff)2] , was fitted
to the a-wave data while allowing Rmax and
S to vary. Three principle observations were made: (1) At
flash intensities ≥0.77 log sc-td-s the leading edge of the normalized
rod ERG a-wave tracks the isolated photoreceptor response across
the first 20 ms or up to the point of b-wave intrusion.
The rod ERG a-wave was essentially identical to the isolated
receptor response for all intensities that produce peak responses within
14 ms after the flash. (2) The best fit of sensitivity (S) was
not affected by APB and/or PDA, suggesting that the inner retina contributes
very little to the dark-adapted a-wave. (3) APB always
reduced the maximum dark-adapted a-wave amplitude (by
15–30%), and PDA always increased it (by 7–15%).
Using the phototransduction model, both events can be interpreted
as a scaling of the photoreceptor dark current. This suggests
that activity of postreceptor cells somehow influences the rod
dark current, possibly by feedback through horizontal cells
(although currently not demonstrated for the rod system), or
by altering the ionic concentrations near the photoreceptors,
or by neuromodulator effects mediated by dopamine or melatonin.
GABAergic visual pathways in the frog Rana pipiens
Authors: LI ZHENG , FITE KATHERINE V.
Published: December 2002

Gamma-aminobutyric acid (GABA) is the most prevalent inhibitory
neurotransmitter in the vertebrate brain. It can exert its
influence either as GABAergic projection pathways or as local
interneurons, which play an essential role in many visual
functions. However, no GABAergic visual pathways have been studied
in frogs so far. In the present study, GABAergic pathways in
the central visual system of Rana pipiens were
investigated with double-labeling techniques, combining
immunocytochemistry for GABA with Rhodamine microspheres for
retrograde tracing. Three GABAergic visual pathways were
identified: (1) a retino-tectal projection, from retina to the
contralateral optic tectum (OT); (2) an ipsilateral projection
from the nucleus of the basal optic root (nBOR) to the pretectal
nucleus lentiformis mesencephali (nLM); and (3) a second-order
pathway from the nucleus isthmi (NI), bilaterally, to the optic
tectum. These results indicate that GABA is involved in both
first-order (retina to optic tectum) as well as second-order
(nucleus isthmi to optic tectum) visual projections in Rana
pipiens, and may play a major role in mediating visuomotor
reflexs such as optokinetic nystagmus or other visually guided
behaviors.
Linear filtering and nonlinear interactions in
direction-selective visual cortex neurons: A noise correlation
analysis
Authors: BAKER CURTIS L.
Published: December 2002

Spatial and temporal properties related to direction selectivity
of both simple and complex type visual cortex neurons were assessed
by cross-correlation analysis of their responses to random ternary
white noise. This stimulus consisted of multiple randomly placed
bars, each colored white, black, or gray with equal probability,
which were rerandomized every 5–10 ms. A first-order
cross-correlation analysis of a neuron's spike train with
the spatiotemporal history of the stimulus provided an estimate
of the neuron's linear spatiotemporal filtering properties.
A nonlinear correlation analysis measured the amount of interaction
for pair-wise combinations of bars as a function of their relative
spatial and temporal separations. The spatiotemporal orientation
of each of these functions was quantified using a “motion
energy index” (MEI), which was compared to the
neurons' direction selectivity measured with drifting sinewave
gratings. Both first-order and nonlinear correlation plots usually
showed s–t orientation whose sign
was consistent with the neuron's direction preference;
however, in many cases the MEI for first-order analysis
was weak compared to that seen in the nonlinear interactions.
The structures of the nonlinear interaction functions were also
compared with predictions from a conventional model of direction
selectivity based on a simple spatiotemporally oriented linear
filter, followed by an intensive nonlinearity (“LN
model”). These comparisons showed that some neurons'
data agreed reasonably well with such a model, while others
agreed poorly or not at all. Simulations of an alternative model
which combines signals from idealized lagged and nonlagged
front-end linear filters produce noise correlation results more
like those seen in the neurophysiological data.
Task-specific reversal of visual hemineglect following bilateral
reversible deactivation of posterior parietal cortex: A comparison
with deactivation of the superior colliculus
Authors: LOMBER STEPHEN G. , PAYNE BERTRAM R.
Published: December 2002

The purpose of the present study was to compare and contrast
behavioral performance on three different tasks of spatial
cognition during unilateral and bilateral reversible deactivation
of posterior parietal cortex. Specifically, we examined posterior
middle suprasylvian (pMS) sulcal cortex in adult cats during
temporary and reversible cooling deactivation. In Task 1, the
cats oriented to a high-contrast, black visual stimulus
moved into the visual field periphery. In Task 2, the
cats oriented to a static light-emitting diode (LED).
Task 3 examined the cats' ability to determine whether
a black-and-white checkered, landmark box was closer
to the right or left side of the testing apparatus. Following
training on all tasks, cryoloops were implanted bilaterally
within the pMS sulcus. Unilateral deactivation of pMS sulcal
cortex resulted in virtually no responses to either moved
or static stimuli and virtually no responses to landmarks
presented in the contralateral hemifield, and a profound
contralateral hemifield neglect was induced. Responses to stimuli
and landmarks presented in the ipsilateral hemifield were
unimpaired. Additive, bilateral cooling of the homotopic region
in the contralateral hemisphere, but not an adjacent region,
resulted in reversal of the initial hemineglect for the
moved stimulus, yet induced a complete failure to orient
to peripheral static LED stimuli. Bilateral cooling
also reversed the contralateral neglect of the landmark,
but then cats could not accurately determine position of the
landmark anywhere in the visual field because performance
was reduced to chance levels for all landmark loci in both
hemifields. In this instance, as the contralateral neglect
disappeared during bilateral cooling of pMS cortex, a new spatial
discrimination deficit was revealed across the entire visual
field. We conclude that pMS cortex contributes in multiple ways
to the analyses of space, and that these contributions cannot
be safely predicted from analyses of unilateral deactivations
or from one task to another. Moreover, it is clear that other
structures are capable of guiding orienting to high contrast,
moved targets when pMS cortex is eliminated from brain
circuitry. However, these same structures are incapable of
supporting either orienting to static stimuli or analyses
of spatial relations as tested with the landmark task.
The impact of reversible deactivation of the superior colliculus
on these same tasks is discussed.
Motion direction signals in the primary visual cortex of
cat and monkey
Authors: GEISLER WILSON S. , ALBRECHT DUANE G. , CRANE ALISON M. , STERN LAWRENCE
Published: December 2002

When an image feature moves with sufficient speed it should
become smeared across space, due to temporal integration in
the visual system, effectively creating a spatial motion pattern
that is oriented in the direction of the motion. Recent
psychophysical evidence shows that such “motion streak
signals” exist in the human visual system. In this study,
we report neurophysiological evidence that these motion streak
signals also exist in the primary visual cortex of cat and monkey.
Single neuron responses were recorded for two kinds of moving
stimuli: single spots presented at different velocities and
drifting plaid patterns presented at different spatial and temporal
frequencies. Measurements were made for motion perpendicular
to the spatial orientation of the receptive field
(“perpendicular motion”) and for motion parallel
to the spatial orientation of the receptive field (“parallel
motion”). For moving spot stimuli, as the speed increases,
the ratio of the responses to parallel versus
perpendicular motion increases, and above some critical speed,
the response to parallel motion exceeds the response to
perpendicular motion. For moving plaid patterns, the average
temporal tuning function is approximately the same for both
parallel motion and perpendicular motion; in contrast, the spatial
tuning function is quite different for parallel motion and
perpendicular motion (band pass for the former and low pass
for the latter). In general, the responses to spots and plaids
are consistent with the conventional model of cortical neurons
with one rather surprising exception: Many cortical neurons
appear to be direction selective for parallel motion. We propose
a simple explanation for “parallel motion direction
selectivity” and discuss its implications for the motion
streak hypothesis. Taken as a whole, we find that the measured
response properties of cortical neurons to moving spot and plaid
patterns agree with the recent psychophysics and support the
hypothesis that motion streak signals are present in V1.
A cGMP-gated channel subunit in Limulus photoreceptors
Authors: CHEN FRANK H. , BAUMANN ARND , PAYNE RICHARD , LISMAN JOHN E.
Published: December 2002

The phototransduction cascade in invertebrate photoreceptors
has not been fully elucidated. It has been proposed that in
Limulus ventral photoreceptor cGMP is the intracellular
second messenger that directly controls the gating of the
light-dependent channels (Johnson et al., 1986; Bacigalupo et
al., 1991). Recently, a putative cGMP-gated channel cDNA,
Lcng1, has been cloned from Limulus and shown
to be expressed in the brain and the ventral eye (Chen et al.,
1999). In this study, we sought to more specifically localize
the LCNG1 transcript and protein. In situ hybridization
was used to determine whether the gene is expressed in glia
or photoreceptor cells in the ventral eye. The results clearly
demonstrated that Lcng1 mRNA is transcribed in the
ventral photoreceptors. On Western blots probed with a polyclonal
antibody raised against the C-terminus of LCNG1, a 100-kDa band
and an 80-kDa band was labeled in the membrane protein preparations
from brain and ventral eye, respectively. The labeling of these
bands was blocked by preabsorption of the antibody with the
antigen, indicating the labeling specificity. Immunocytochemistry
and confocal microscopy were applied to investigate the subcellular
localization of this antigen. Immunolabeling was highly localized
in the transducing lobes of ventral eye photoreceptors and lateral
eye photoreceptors. In both cases, the labeling was associated
with membrane regions specialized for phototransduction, but
the exact pattern appeared to be somewhat different in the two
eyes. Preabsorption of the antiserum with antigen abolished
the labeling, confirming specificity. The results lend support
to the hypothesis that a cGMP-gated channel is directly involved
in the phototransduction process.
Cortical mapping of gamma oscillations in areas V1 and V4
of the macaque monkey
Authors: ROLS GABRIEL , TALLON-BAUDRY CATHERINE , GIRARD PASCAL , BERTRAND OLIVIER , BULLIER JEAN
Published: December 2002

To characterize the temporal and spatial parameters of gamma
activity evoked by visual stimuli in areas V1 and V4 of the
monkey cortex, we recorded the electrocorticogram (ECoG) with
an implanted array of 28 and 31 subdural electrodes placed over
the surface of the operculum in two anesthetized monkeys. This
intermediate level of recordings should help to bridge the gap
between multiunit and scalp recordings. Both averaged and
single-trial responses to small flashed stimuli, for which we
varied the retinotopic position, the luminance and the color,
were analyzed in the time-frequency domain using a wavelet-based
decomposition of the signal. Large gamma oscillations (40–55
Hz), not phase locked to stimulus onset, were observed during
the whole stimulus presentation, whereas visual evoked potentials
(VEPs) were present mainly at stimulus onset and offset. Cortical
mapping showed that both activities were restricted in spatial
extent and followed the retinotopic organization of area V1
on the operculum, thus strongly suggesting they were generated
in the underlying cortex. Oscillatory burst detection in single
trials showed that one to two bursts lasting from 100 ms to
500 ms occurred in the first 500 ms following stimulus onset,
and that bursts occurring during the subsequent phases of the
response had a smaller amplitude and duration. Finally, we showed
that gamma activity was stronger with higher luminances and
for red than for green, yellow, or white stimuli of same luminance.
In one animal we recorded gamma activity over area V4. This
was of lower magnitude than the activity recorded over V1 and
was delayed by 40 ms with respect to the beginning of gamma
activity in V1, in contrast with the VEPs that were delayed
by 20 ms only. Both gamma oscillations and early VEP followed
the retinotopic organization of V4 over the prelunate gyrus.
The results show that gamma oscillations are dependent upon
the same parameters as the VEPs (retinotopic position, luminance,
and color). However, the differences in the time course of VEPs
and gamma activity (transient vs. sustained) suggests
that these two responses may reflect different cell populations,
different networks, or different firing modes.
N-cholinergic facilitation of glutamate release from an
individual retinotectal fiber in frog
Authors: KURAS A. , GUTMANIENĖ N.
Published: December 2002

Nicotinic acetylcholine receptors are localized on retinotectal
axons' terminals in lower vertebrates. The effects of activation
of these receptors by endogenous acetylcholine were observed under
stimulation of mass optic fibers. This study was designed to determine
whether endogenous acetylcholine facilitates frog retinotectal
transmission, provided only the synapses of an individual optic
axon are activated, and to evaluate the feasible extent of
nicotinic facilitation in these synapses by applied agonist.
To this end, the effects of cholinergic drugs on the extracellular
action and synaptic potentials recorded from the terminal
arborization of a separate retinotectal fiber (in layer F of
the tectum) were investigated in vivo. Glutamatergic
nature of retinotectal synapses was reexamined by treatment
with kynurenic acid. Both kynurenic acid (0.25–1 mM) and
d-tubocurarine chloride (10–15 μM) significantly
depressed the synaptic potentials. Carbamylcholine chloride
(50–150 μM) evoked a large augmentation of the synaptic
potentials and a slight but statistically significant decrease
of the action potentials. D-tubocurarine reduced the effect
of carbamylcholine. Pilocarpine hydrochloride (50 μM) had
only a weak effect. The paired-pulse facilitation of the synaptic
potentials changed significantly under the action of
carbamylcholine and d-tubocurarine. The obtained results suggest
that the glutamate release from activated synapses of individual
retinotectal axons is facilitated by endogenous acetylcholine
via presynaptic nicotinic receptors. Under used
stimulation conditions, this modulation mechanism was employed
only partially since its activation by applied carbamylcholine
could enhance synaptic transmission up to 2.8 times.
Development of cholinergic amacrine cell stratification in
the ferret retina and the effects of early excitotoxic ablation
Authors: REESE B.E. , RAVEN M.A. , GIANNOTTI K.A. , JOHNSON P.T.
Published: December 2002

The present study has examined the emergence of cholinergic
stratification within the developing inner plexiform layer (IPL),
and the effect of ablating the cholinergic amacrine cells on
the formation of other stratifications within the IPL. The
population of cholinergic amacrine cells in the ferret's
retina was identified as early as the day of birth, but their
processes did not form discrete strata until the end of the
first postnatal week. As development proceeded over the next
five postnatal weeks, so the positioning of the cholinergic
strata shifted within the IPL toward the outer border, indicative
of the greater ingrowth and elaboration of processes within
the innermost parts of the IPL. To examine whether these
cholinergic strata play an instructive role upon the development
of other stratifications which form within the IPL, one-week-old
ferrets were treated with l-glutamate in an attempt
to ablate the population of cholinergic amacrine cells. Such
treatment was shown to be successful, eliminating all of the
cholinergic amacrine cells as well as the alpha retinal ganglion
cells in the central retina. The remaining ganglion cell classes
as well as a few other retinal cell types were partially reduced,
while other cell types were not affected, and neither retinal
histology nor areal growth was compromised in these ferrets.
Despite this early loss of the cholinergic amacrine cells, which
are eliminated within 24 h, other stratifications within the
IPL formed normally, as they do following early elimination
of the entire ganglion cell population. While these cholinergic
amacrine cells are present well before other cell types have
differentiated, apparently neither they, nor the ganglion cells,
play a role in determining the depth of stratification for other
retinal cell types.
Retinal acetylcholine content in normal and myopic eyes:
A role in ocular growth control?
Authors: McBRIEN NEVILLE A. , COTTRIALL CHARLES L. , ANNIES ROGER
Published: December 2002

Retinal neurotransmitters are known to play a role in postnatal
ocular development and eye growth. The success of muscarinic
antagonists in blocking form-deprivation myopia has implicated
retinal acetylcholine in the control of ocular growth. The present
study investigated whether steady-state content of acetylcholine
(ACh) and its metabolite choline (Ch) are altered in the retina
of eyes developing axial myopia, in both tree shrews and chicks.
Retinal ACh and Ch content were measured using reverse-phase
high-performance liquid chromatography. Posterior and anterior
retinal samples were analyzed from myopic (form deprived) and
control eyes as well as age-matched normal eyes. Normative data
on retinal neurotransmitter content demonstrated that chick
retinas contained less than half the ACh and Ch neurotransmitter
content of tree shrews when normalized to retinal protein (ACh:
61 ± 3 vs. 130 ± 6 ng, Ch: 131 ±
5 vs. 347 ± 25 ng). There was no significant
difference in either ACh or Ch content between myopic and
contralateral control eyes in either tree shrews or chicks,
irrespective of the degree of myopia. This finding was consistent
for both posterior, anterior, and consequently whole retinal
samples. In contrast, dopamine and DOPAC contents were found
to be reduced in myopic compared to control eyes of the same
tree shrews (dopamine −6.9% and DOPAC −15.5%) and
chicks (dopamine −12.3% and DOPAC −28.2%). These
findings demonstrate that, contrary to dopamine and DOPAC content,
steady-state retinal acetylcholine and choline content is not
significantly altered during myopia development.
Effects of light adaptation on contrast processing in bipolar
cells in the retina
Authors: FAHEY PATRICK K. , BURKHARDT DWIGHT A.
Published: December 2002

Effects of light adaptation on contrast processing in the outer
retina were investigated over nearly four decades of background
illumination by analyzing the intracellular responses of 111
bipolar cells, 66 horizontal cells, and 22 cone photoreceptors
in the superfused eyecup of the tiger salamander (Ambystoma
tigrinum). Light adaptation had striking and similar effects
on the average contrast responses of the hyperpolarizing (Bh)
and depolarizing (Bd) classes of bipolar cells: Over the lower
two decades of background illumination, the contrast gain increased
7-fold to reach values as high as 20–30, the dynamic range
and the half-maximum contrast decreased by about 60%, the total
voltage range increased some 40%, and contrast dominance changed
from highly positive to more balanced. At higher levels of
background, most aspects of the contrast response stabilized
and Weber's Law then held closely. In this background range,
the contrast gain of bipolar cells was amplified some 20×
relative to that of cones whereas the corresponding amplification
in horizontal cells was about 6×. Differences in the growth
of contrast gain with the intensity of the background illumination
for cones versus bipolar cells suggest that there are
at least two adaptation-dependent mechanisms regulating contrast
gain. One is evident in the cone photoresponse such that an
approximately linear relation holds between the steady-state
hyperpolarization and contrast gain. The other arises between
the voltage responses of the cones and bipolar cells. It could
be presynaptic (modulation of cone transmitter release by
horizontal cell feedback or other mechanisms) and/or postsynaptic,
that is, intrinsic to bipolar cells. Contrast gain grew with
the background intensity by a larger factor in horizontal than
in bipolar cells. This provides a basis for the widely held
view that light adaptation increases the strength of surround
antagonism in bipolar cells. On average, the effects of light
adaptation and most quantitative indices of contrast processing
were remarkably similar for Bd and Bh cells, implying that both
classes of bipolar cells, despite possible differences in
underlying mechanisms, are about equally capable of encoding
all primary aspects of contrast at all levels of light adaptation.
Metabolic activity in optic tectum during regeneration of
retina in adult goldfish
Authors: MELZER PETER , POWERS MAUREEN K.
Published: December 2002

Retinal and visual function returns following retinal destruction
by ouabain in adult goldfish (Carassius auratus). Although
the precise cellular mechanisms are unclear, the ability to
regenerate CNS neurons and connections that subsequently sustain
visual behavior is remarkable, especially for an adult vertebrate.
In this paper, we ask whether visual stimulation via
new retinal cells can activate existing cells in the optic tectum,
which normally receives the largest retinal projection in this
species. The right eyes of adult goldfish were injected with
ouabain. After 1–18 weeks the conscious, freely moving
fish were exposed to spatially and temporally varying visual
stimuli and the resulting tectal metabolic activity was determined
with the autoradiographic deoxyglucose method. In normal controls
without lesions, visual stimulation produced equally strong
metabolic activity in both tectal hemispheres, peaking in the
layer where most retinotectal projections terminate (N
= 6). One week after ouabain injection, metabolic activity in
the contralateral, deprived tectum was dramatically reduced
(N = 5), closely resembling the effect of unilateral
ocular enucleation (N = 5). However, 9–18 weeks
after ouabain injection, metabolic activity in the deprived
tectum recovered to a level that was statistically
indistinguishable from normal controls (N = 6). These
findings suggest that, after a comprehensive cytotoxic lesion
of the retina, regenerated ganglion cells not only establish
new connections with the preexisting optic tectum, but also
effectively transmit visual information they receive from newly
generated photoreceptors to the “old” tectum.
Development of postreceptoral function in pigmented and albino
guinea pigs
Authors: VINGRYS ALGIS J. , BUI BANG V.
Published: December 2002

Retinal neurons are generated in overlapping growth spurts
with ganglion cell and cone populations peaking sooner than
rod and bipolar cell numbers. As such the functional development
of the inner and outer retinal components and elements within
these strata (rods vs. cones) may differ. We considered
the postnatal development of the postreceptoral components of
the ERG (P2, oscillatory potentials) in the guinea pig. ERGs
were also evaluated across albino and pigmented strains in order
to consider the role that pigmentation has for functional
development. Electroretinograms were collected on postnatal
days PD1 to PD60 (n = 4–7 per time point).
The postreceptoral P2 amplitude and implicit time was extracted
(digital subtraction of modelled P3 and filtering,
0.5–49 Hz). Intensity–response relationships were
described using Naka–Rushton functions whose parameters
were compared using a nonparametric bootstrap. Oscillatory
potentials (OPs) were extracted following signal conditioning
and filtering to remove the a- and b-waves
and were described using a Gabor function. OP response parameters
were compared using repeated measures ANOVA. Postreceptoral
P2 amplitudes mature soon after birth (PD10–PD12).
Oscillatory potentials show a similar postnatal amplitude
development (PD10–PD12) but a later maturation in timing
(PD20) compared with the postreceptoral waveform. All components
(P3, P2, and OPs) declined at the same relative rate with age
after PD12. Albino animals gave larger, faster, and more sensitive
waveforms at all ages but showed the same age-related trends
as did pigmented animals. Early development of inner retinal
synapses in guinea pigs may underlie the rapid postnatal maturation
of their postreceptoral response. These appear to be constrained
by the development of receptoral responses. All components declined
at the same rate suggesting either a change in the photoreceptoral
response or changes to ocular impedance with age.
Transgenic expression of the jellyfish green fluorescent
protein in the cone photoreceptors of the mouse
Authors: FEI YIJIAN , HUGHES THOMAS E.
Published: December 2002

The goal of this study was to determine whether the jellyfish
green fluorescent protein (GFP) could be used in transgenic
mice to label and purify cone photoreceptors from the living
retina. We created a transgene containing the 5′ regulatory
sequence of the human red pigment gene (pR6.5 lacZ clone; kindly
provided by J. Nathans & Y. Wang), fused to the GFP coding
sequence. This transgene was used to generate seven lines of
PCR-positive founders. Three of the lines had bright green
fluorescent cone photoreceptors. The GFP fills the entire cell.
Two mouse lines had only a few (∼10–100) fluorescent
cells per retina, and one line (R6.85933) had many thousands.
In the latter, double labeling of the cones with RITC-conjugated
peanut agglutinin reveals that in the ventral retina a small
proportion of the cones express GFP, while in the dorsal retina
the majority do. Cells dissociated from the retinae of line
R6.85933 continue to fluoresce and can be readily detected and
enriched with flow cytometry. The signal provides a log unit
of separation between the fluorescent cone soma and the remaining
retinal cells. Roughly 3% of the cells are this fluorescent,
and it is possible to purify up to 30,000 cells from one mouse.
RT-PCR analysis of the mRNA from these isolated cells detects
both the middle and short wavelength opsins with little if any
contamination from rhodopsin.
Inhibitors of guanylate cyclase inhibit phototransduction
in Limulus ventral photoreceptors
Authors: GARGER ALEX , RICHARD EDWIN A. , LISMAN JOHN E.
Published: December 2002

The second messenger systems involved in the final stages of
the phototransduction cascade in Limulus photoreceptors
remain unclear. Excised patches of transducing membrane contain
cGMP-gated channels, suggesting the involvement of cGMP in the
excitation process. To further explore this possibility, we tested
the effects of inhibitors and agonists of guanylate cyclase. The
active site cyclase inhibitors guanosine 5′-tetraphosphate
and adenosine 5′-tetraphosphate produced a reversible reduction
of the response to light without affecting resting membrane properties.
The cyclase inhibitor Rp-GTPαS produced
a similar reduction, but the effect was only slightly reversible. The
reduction in the response produced by these inhibitors was robust, often
producing over a 95% decrease in the amplitude of the light
response. Previous work had shown that an end-product cyclase
inhibitor, imidodiphosphate, also inhibited the response. The
consistent results with four different guanylate cyclase inhibitors
strongly support the involvement of this enzyme in the
phototransduction cascade. To determine whether the guanylate
cyclase involved is the NO-dependent soluble form, we applied
inhibitors and activators of the nitric oxide synthase/guanylate
cyclase pathway such as L-N5-(1-iminoethyl) ornithine,
sodium nitroprusside, and carboxy-PTIO. None of these agents had any
substantial effect on phototransduction. Taken together, these results
support a role for a particulate guanylate cyclase in Limulus
photoreceptor excitation.
Transneuronal retrograde transport of attenuated pseudorabies
viruses within central visual pathways
Authors: MOORE RODNEY J. , VINSANT SHERRY , McCAULEY ANITA K. , KURUKULASURIYA NUWAN C. , GODWIN DWAYNE W.
Published: December 2002

Pseudorabies virus (PRV) has been shown to be an effective
transneuronal tracer within both the peripheral and the central
nervous system. The only investigations of this virus in the
visual system have examined anterograde transport of PRV from
injection sites in the retina. In the present study, we injected
attenuated forms of PRV into the primary visual cortex of both
rats and cats to determine whether transneuronal retrograde
infection would occur back to the retina. In rats, we made small
injections into visual cortex of a strain of PRV (Bartha Blu)
that contained a β-galactosidase promoter insert. In cats,
we injected PRV-M201 into area V1 of visual cortex. After a
2- to 4-day incubation period, we examined tissue from these
animals for the presence of the β-galactosidase marker (rats)
or the virus itself (cats). Cortical PRV injections resulted
in transneuronal retrograde infection of the lateral geniculate
nucleus (LGN), thalamic reticular nucleus (TRN), and retina.
PRV was retinotopically distributed in the pathway. In addition,
double-labeling experiments in cats using an antibody against
gamma-aminobutyric acid (GABA) were conducted to reveal PRV-labeled
interneurons within the LGN and TRN. All TRN neurons were GABA+,
as was a subset of LGN neurons. Only the subset of TRN neurons
adjacent to the PRV-labeled sector of LGN was labeled with PRV.
In addition, a subset of GABA+ interneurons in LGN was also
labeled with PRV. We processed some tissue for electron microscopy
to examine the morphology of the virus at various replication
stages. No mature virions were detected in terminals from efferent
pathways, although forms consistent with retrograde infection
were encountered. We conclude that the PRV strains we have used
produce a local infection that progresses primarily in the
retrograde direction in the central visual pathways. The infection
is transneuronal and viral replication maintains the intensity
of the label throughout the chain of connected neurons, providing
a means of examining detailed circuitry within the visual pathway.
Absolute and relative sensitivity of the scotopic system
of rat: Electroretinography and behavior
Authors: NAARENDORP FRANK , SATO YOSHINORI , CAJDRIC AIDA , HUBBARD NICOLE P.
Published: December 2002

The goal of the present study was to relate the dark and
light-adapted flash sensitivity of the scotopic threshold response
(STR) and rod b-wave of the electroretinogram (ERG)
to behaviorally measured rod increment threshold responses.
Small amplitudes of the dark-adapted STR and b-wave,
the latter after application of NMDA, were found to increase
in proportion to flash intensity. The value obtained for the
sensitivity of the b-wave would be expected if signals
from rods were summed linearly by the rod bipolar cell. The
sensitivity of the STR could not be accounted for in terms of
rod signal convergence as the source of this ERG component is
still unknown. Increment threshold responses of rats were measured
behaviorally in an operant conditioning chamber. At absolute
threshold, on average 1 in 2400 rods were activated by the test
flash. Comparison of the adaptive effects of background lights
on behaviorally measured scotopic sensitivity and rod ERG
sensitivity suggest that the increment threshold sensitivity
of rat is regulated at three different sites in the retina.
The psychophysical periphery effect crosses the vertical meridian
Authors: KUYK THOMAS , NICULESCU DIANA
Published: December 2002

This study measured the periphery effect and compared its
magnitude when the peripheral stimulation was on the same or
opposite side of the vertical meridian as the test spot. Test
thresholds for a 1.5-deg diameter, 8-ms spot located 1.75 deg
to one side of the vertical meridian were elevated by approximately
0.125 log units when a 0.25 cycles/deg (cpd) counterphased grating
was presented at a similar eccentric offset on the other side
of the vertical meridian. The periphery effect disappeared when
the test spot was moved outward to 8-deg eccentricity. When
the grating and test were presented on the same side of the
vertical meridian, test thresholds at both retinal locations
were elevated by the same amount, 0.2 log units. Consistent
with the physiology in cat retina, the periphery effect in humans
also crosses over the vertical meridian. However, the effect
is small and the test spot must be in close proximity to the
vertical meridian for it to be observed. Also, the crossover
periphery effect is reduced in magnitude by 37.5% compared to
when the grating and test are presented on the same side of
the vertical meridian. This suggests there may be a difference
in how the underlying neural mechanism that transmits the periphery
effect signal laterally is organized for sending the periphery
effect signal across the vertical meridian as compared to within
a retinal hemifield.