bluuebunny/crossref_metadata_2025 huggingface dataset:
Dopaminergic and GABAergic amacrine cells are direct targets
of melatonin: Immunocytochemical study of mt1
melatonin receptor in guinea pig retina
Authors: FUJIEDA HIROKI , SCHER JUDITE , HAMADANIZADEH SOHEILA A. , WANKIEWICZ ELLEN , PANG SHIU F. , BROWN GREGORY M.
Published: July 2002

Distribution of the mt1 melatonin receptor
in the guinea pig retina was immunocytochemically investigated
using peptide-specific anti-mt1 receptor antibody.
Western blots of the guinea pig retina showed a single
band at approximately 37 kilodalton (kD) immunoreactive
to the anti-mt1 antibody. The most intense immunoreactivity
for the mt1 receptor was detected in the cell
bodies of ganglion cells. Their dendrites and axons were
also immunolabeled. Subpopulations of amacrine cells, the
inner plexiform layer, and the outer plexiform layer also
exhibited moderate to weak immunolabeling. The mt1-positive
amacrine cells were located either at the vitreal border
of the inner nuclear layer or displaced in the ganglion
cell layer. Double immunolabeling using antibodies to the
mt1 receptor and tyrosine hydroxylase revealed
that the majority of dopaminergic amacrine cells showed
mt1 immunoreactivity. Almost all the 1CA type
dopaminergic cells were mt1 positive while the
2CA type cells less frequently exhibited mt1
immunoreaction. By double immunolabeling for the mt1
receptor and GABA, more than 50% of the mt1-immunoreactive
amacrine cells were shown to be GABAergic neurons. Approximately
one-third of the GABAergic amacrine cells were immunolabeled
for the mt1 receptor. The present results demonstrate
expression of the mt1 receptor in diverse neuronal
cell types in the guinea pig retina and provide the first
evidence for the direct effect of melatonin on dopaminergic
and GABAergic amacrine cells via the mt1
receptor.
Motion coherence affects human perception and pursuit similarly
Authors: BEUTTER BRENT R. , STONE LELAND S.
Published: July 2002

Pursuit and perception both require accurate information
about the motion of objects. Recovering the motion of objects
by integrating the motion of their components is a difficult
visual task. Successful integration produces coherent global
object motion, while a failure to integrate leaves the
incoherent local motions of the components unlinked. We
compared the ability of perception and pursuit to perform
motion integration by measuring direction judgments and
the concomitant eye-movement responses to line-figure parallelograms
moving behind stationary rectangular apertures. The apertures
were constructed such that only the line segments corresponding
to the parallelogram's sides were visible; thus, recovering
global motion required the integration of the local segment
motion. We investigated several potential motion-integration
rules by using stimuli with different object, vector-average,
and line-segment terminator-motion directions. We used
an oculometric decision rule to directly compare direction
discrimination for pursuit and perception. For visible
apertures, the percept was a coherent object, and both
the pursuit and perceptual performance were close to the
object-motion prediction. For invisible apertures, the
percept was incoherently moving segments, and both the
pursuit and perceptual performance were close to the terminator-motion
prediction. Furthermore, both psychometric and oculometric
direction thresholds were much higher for invisible apertures
than for visible apertures. We constructed a model in which
both perception and pursuit are driven by a shared motion-processing
stage, with perception having an additional input from
an independent static-processing stage. Model simulations
were consistent with our perceptual and oculomotor data.
Based on these results, we propose the use of pursuit as
an objective and continuous measure of perceptual coherence.
Our results support the view that pursuit and perception
share a common motion-integration stage, perhaps within
areas MT or MST.
NMDAR-1 staining in the lateral geniculate nucleus of normal
and visually deprived cats
Authors: ZIBURKUS JOKUBAS , BICKFORD MARTHA E. , GUIDO WILLIAM
Published: July 2002

In normal adult cats, a monoclonal antibody directed
toward the NR-1 subunit of the N-methyl-d-aspartate
(NMDA) receptor (Pharmingen, clone 54.1) produced dense
cellular and neuropil labeling throughout all layers of
the lateral geniculate nucleus (LGN) and adjacent thalamic
nuclei, including the thalamic reticular, perigeniculate,
medial intralaminar, and ventral lateral geniculate nuclei.
Cellular staining revealed well-defined somata, and in
some cases proximal dendrites. NMDAR-1 cell labeling was
also evident in the LGN of early postnatal kittens, suggesting
that developing LGN cells possess this receptor subunit
at or before eye opening. Within the A-layers of the adult
LGN, staining encompassed a wide range of soma sizes. Soma
size comparisons of NMDAR-1 stained cells with those stained
with an antibody directed toward a nonphosphorylated neurofilament
protein (SMI-32), which selectively stains Y-relay cells
(Bickford et al., 1998), or an antibody to glutamic acid
decarboxylase (GAD), which stains for GABAergic interneurons,
suggested that NMDA receptors are utilized by relay cells
and interneurons. NMDAR-1 staining was also observed in
the LGN of cats with early monocular lid suture. Although
labeling was apparent in both deprived and nondeprived
A-layers of LGN, the distribution of soma sizes was significantly
different. In the deprived A-layers of LGN, staining was
limited to small- and medium-sized cells. Cells with relatively
large soma were lacking. However, cell density measurements
as well as soma size comparisons with cells stained for
Nissl substance suggested these differences were due to
deprivation-induced cell shrinkage and not to a loss of
NMDAR-1 staining in Y-cells. Taken together, these results
suggest that NMDA receptors are utilized by both relay
cells and interneurons in LGN and that alterations in early
visual experience do not necessarily affect the expression
of NMDA receptors in the LGN.
Chloride efflux inhibits single calcium channel open probability
in vertebrate photoreceptors: Chloride imaging and cell-attached
patch-clamp recordings
Authors: THORESON WALLACE B. , NITZAN RON , MILLER ROBERT F.
Published: July 2002

The present study uses cell-attached patch-recording
techniques to study the single-channel properties of Ca2+
channels in isolated salamander photoreceptors and investigate
their sensitivity to reductions in intracellular Cl−.
The results show that photoreceptor Ca2+ channels
possess properties similar to L-type Ca2+ channels
in other preparations, including (1) enhancement of openings
by the dihydropyridine agonist, (−)BayK8644; (2)
suppression by a dihydropyridine antagonist, nisoldipine;
(3) single-channel conductance of 22 pS with 82 mM Ba2+
as the charge carrier; (4) mean open probability of 0.1;
(5) open-time distribution fit with a single exponential
(τ0 = 1.1 ms) consistent with a single open
state; and (6) closed time distribution fit with two exponentials
(τc1 = 0.7 ms, τc2 = 25.4
ms) consistent with at least two closed states. Using a
Cl−-sensitive dye to measure intracellular
[Cl−], it was found that perfusion
with gluconate-containing, low Cl− medium
depleted intracellular [Cl−].
It was therefore possible to reduce intracellular
[Cl−] by perfusion with a low
Cl− solution while maintaining the extracellular
channel surface in high Cl− pipette
solution. Under these conditions, the single-channel
conductance was unchanged, but the mean open probability
fell to 0.03. This reduction can account for the 66% reduction
in whole-cell Ca2+ currents produced by perfusion
with low Cl− solutions. Examination of
the open and closed time distributions suggests that the
reduction in open probability arises from increases in
closed-state dwell times. Changes in intracellular
[Cl−] may thus modulate
photoreceptor Ca2+ channels.
Visual adaptation modulates a potassium conductance in retinular
cells of the crayfish
Authors: MILLER C.S. , GLANTZ R.M.
Published: July 2002

Crayfish photoreceptors exhibit a voltage-dependent
potassium conductance, GK, that is
generally similar to the delayed rectifier channel described
in neurons and other arthropod retinular cells.
GK activation (i.e. the apparent threshold,
Vth) occurs near the resting potential and
GK is substantially reduced by 25 mM
extracellular tetraethylammonium (TEA) and by intracellular
Cs+ injections. Light exposure, sufficient to
reduce visual sensitivity 100-fold, increases
Vth (shifts it in the depolarizing
direction) by about 20 mV. The light-dependent change in
Vth does not depend upon the corresponding
increase (depolarization) of the steady-state membrane potential
nor does it depend upon inward calcium currents. Vth
is slightly influenced by fluctuations in Ko
associated with the light-elicited currents. During light
exposure Ko (measured with K+-sensitive
electrodes) increases by 2.1 mM (equivalent to an 8 mV
increase in EK). This increase in
EK makes only a modest contribution
to the light-dependent change in Vth as
determined by perfusion with high potassium salines. Intracellular
calcium injections increase Vth by 10 to 20
mV and reduce visual sensitivity by 5- to 10-fold. The
results imply that during exposure to high levels of illumination,
K+ currents at the steady-state membrane potential
are diminished by a calcium-dependent change in GK
gating and, to a smaller degree, by a reduced K+
concentration gradient. It is notable that Ca2+ appears
to inhibit both GK and the light-elicited
conductance from both inside and outside the plasma membrane. As a
consequence of the light-dependent change in Vth, GK makes only modest contributions to the changes
in sensitivity and speed normally associated with light adaption.
These functions are regulated by the transduction pathway and are
revealed at the resting potential in the time course and magnitude
of the light-elicited currents.
A temporal model for early vision that explains detection
thresholds for light pulses on flickering backgrounds
Authors: SNIPPE H.P. , POOT L. , van HATEREN J.H.
Published: July 2002

A model is presented for the early (retinal) stages of
temporal processing of light inputs in the visual system.
The model consists of a sequence of three adaptation processes,
with two instantaneous nonlinearities in between. The three
adaptation processes are, in order of processing of the
light input: a divisive light adaptation, a subtractive
light adaptation, and a contrast gain control. Divisive
light adaptation is modeled by two gain controls. The first
of these is a fast feedback loop with square-root behavior,
the second a slow feedback loop with logarithm-like behavior.
This can explain several aspects of the temporal behavior
of photoreceptor outputs. Subtractive light adaptation
is modeled by a high-pass filter equivalent to a fractional
differentiation, and it can explain the attenuation of
low frequencies observed in ganglion cell responses. Contrast
gain control in the model is fast (Victor, 1987), and can
explain the decreased detectability of test signals that
are superimposed on dynamic backgrounds. We determine psychophysical
detection thresholds for brief test pulses that are presented
on flickering backgrounds, for a wide range of temporal
modulation frequencies of these backgrounds. The model
can explain the psychophysical data for the full range
of modulation frequencies tested, as well as detection
thresholds obtained for test pulses on backgrounds with
increment and decrement steps in intensity.
Computational analysis of vertebrate phototransduction:
Combined quantitative and qualitative modeling of dark-
and light-adapted responses in amphibian rods
Authors: HAMER RUSSELL D.
Published: July 2002

We evaluated the generality of two models of vertebrate
phototransduction. The approach was to quantitatively optimize
each model to the full waveform of high-quality, dark-adapted
(DA), salamander rod flash responses. With the optimal
parameters, each model was then used to account for signature,
qualitative features of rod responses from three experimental
paradigms (stimulus/response, “S/R suite”):
(1) step responses; (2) the intensity dependence of the period
of photocurrent saturation (Tsatvs. ln(I)); and (3) light-adapted (LA)
incremental flash sensitivity as a function of background
intensity. The first model was the recent successful model
of Nikonov et al. (1998). The second model replaced the
instantaneous Ca2+ buffering used in the Nikonov
et al. model with a dynamic buffer. The results showed
that, in the absence of the dynamic Ca2+ buffer,
the Nikonov et al. model does not have sufficient flexibility
to provide a good fit to the flash responses, and,
using the same parameters, reproduce the salient features
of the S/R suite—critical features at step onset and
offset are absent; the Tsat function
has too shallow a slope; and the model cannot generate the
empirically observed I-range of Weber–Fechner
LA behavior. Some features could be recovered by changing
parameters, but only at the expense of the fit to the reference
(Ref) data. When the dynamic buffer is added, the model
is able to achieve an acceptable fit to the Ref data
while reproducing several features of the S/R suite, including
an empirically observed Tsat
function, and an extended range of LA flash sensitivity
adhering to Weber's law. The overall improved behavior
of the model with a dynamic Ca2+ buffer indicates
that it is an important mechanism to include in a working
model of phototransduction, and that, despite the slow
kinetics of amphibian rods, Ca2+ buffering should
not be simulated as an instantaneous process. However,
neither model was able to capture all the features with
the same parameters yielding the optimal fit to the Ref
data. In addition, neither model could maintain a good
fit to the Ref data when five key biochemical parameters
were held at their current known values. Moreover, even
after optimization, a number of important parameters remained
outside their empirical estimates. We conclude that other
mechanisms will need to be added, including additional
Ca2+-feedback mechanisms. The present research
illustrates the importance of a hybrid qualitative/quantitative
approach to model development, and the limitations of modeling
restricted sets of data.
Amacrine, ganglion, and displaced amacrine cells in the
rabbit retina express nicotinic acetylcholine receptors
Authors: KEYSER KENT T. , MACNEIL MARGARET A. , DMITRIEVA NINA , WANG FAN , MASLAND RICHARD H. , LINDSTROM JON M.
Published: July 2002

Acetylcholine (ACh) in the vertebrate retina affects
the response properties of many ganglion cells, including
those that display directional selectivity. Three β
and eight α subunits of neuronal nicotinic acetylcholine
receptors (nAChRs) have been purified and antibodies have
been raised against many of them. Here we describe biochemical
and immunocytochemical studies of nAChRs in the rabbit retina.
Radioimmunoassay and Western blot analysis demonstrated that
many of the nAChRs recognized by a monoclonal antibody (mAb210)
contain β2 subunits, some of which are in combination with
α3 and possibly other subunits. MAb210-immunoreactive
cells in the inner nuclear layer (INL) were 7–14
μm in diameter and were restricted to the innermost
one or two tiers of cells, although occasional cells were
found in the middle of the INL. At least 60% of the cells
in the ganglion cell layer (GCL) in the visual streak displayed
mAb210 immunoreactivity; these neurons ranged from 7–18
μm in diameter. The dendrites of cells in both the
INL and GCL could sometimes be followed until they entered
one of two dense, poorly defined, bands of processes in
the inner plexiform layer (IPL) that overlap the arbors
of the cholinergic starburst cells. Parvalbumin and serotonin-positive
neurons did not exhibit nAChR immunoreactivity. Although
the level of receptor expression appeared to be low, mAb210
immunoreactivity was observed in some of the ChAT-positive
(starburst) amacrine cells.
Temporal dynamics of motion integration for the initiation
of tracking eye movements at ultra-short latencies
Authors: MASSON GUILLAUME S. , RYBARCZYK YVES , CASTET ERIC , MESTRE DANIEL R.
Published: July 2002

The perceived direction of a grating moving behind an
elongated aperture is biased towards the aperture's
long axis. This “barber pole” illusion is a
consequence of integrating one-dimensional (1D) or grating
and two-dimensional (2D) or terminator motion signals.
In humans, we recorded the ocular following responses to
this stimulus. Tracking was always initiated at ultra-short
latencies (≈ 85 ms) in the direction of grating motion.
With elongated apertures, a later component was initiated
15–20 ms later in the direction of the terminator
motion signals along the aperture's long axis. Amplitude
of the later component was dependent upon the aperture's
aspect ratio. Mean tracking direction at the end of the
trial (135–175 ms after stimulus onset) was between
the directions of the vector sum computed by integrating
either terminator motion signals only or both grating and
terminator motion signals. Introducing an elongated mask
at the center of the “barber pole” did not
affect the latency difference between early and later components,
indicating that this latency shift was not due to foveal
versus peripheral locations of 1D and 2D motion signals.
Increasing the size of the foveal mask up to 90% of the
stimulus area selectively reduced the strength of the grating
motion signals and, consequently, the amplitude of the
early component. Conversely, reducing the contrast of,
or indenting the aperture's edges, selectively reduced
the strength of terminator motion signals and, consequently,
the amplitude of the later component. Latencies were never
affected by these manipulations. These results tease apart
an early component of tracking responses, driven by the
grating motion signals and a later component, driven by
the line-endings moving at the intersection between grating
and aperture's borders. These results support the
hypothesis of a parallel processing of 1D and 2D motion
signals with different temporal dynamics.
Role of the low-affinity NGF receptor (p75) in survival
of retinal bipolar cells
Authors: WEXLER ERIC M. , BERKOVICH OKSANA , NAWY SCOTT
Published: July 2002

We have examined the role of neurotrophins in promoting
survival of mammalian rod bipolar cells (RBC) in culture.
Retinas taken from 8- to 10-day-old Long-Evans rats were
dissociated and cultured in media supplemented with either
nerve growth factor (NGF), neurotrophin-3 (NT-3), brain-derived
neurotrophic factor (BDNF), ciliary neurotrophic factor
(CNTF), or basic fibroblast growth factor (FGF-2). Survival
was measured by the number of cells that were immunoreactive
for α-, β-, γ-PKC, a bipolar cell-specific
marker. Compared to untreated cultures, CNTF had no effect
on RBC survival, while NGF and NT-3 increased survival
only slightly. BDNF, however, increased survival by approximately
300%. Similar results were obtained with FGF-2. Both nerve
growth factor (NGF) and an antibody (anti-REX) which interferes
with binding to the 75-kD low-affinity neurotrophin receptor
(p75NTR) eliminated BDNF-promoted survival,
but had no effect on FGF-2-mediated survival. Interestingly,
p75NTR was expressed by retinal glia (Müller
cells), but not by the bipolar cells themselves, providing
for the possibility that BDNF might induce Müller
cells to produce a secondary factor, perhaps FGF-2, which
directly rescues RBCs. In support of this hypothesis, an
antibody that neutralizes FGF-2 attenuated the trophic
effects of BDNF, and dramatically reduced survival in cultures
with no added growth factors, indicating that there may
be an endogenous source of FGF-2 that promotes survival
of RBCs in culture. We suggest that BDNF increases production
or release of FGF-2 by binding to p75NTR on
Müller cells.
Responses of ganglion cells to contrast steps in the light-adapted
retina of the tiger salamander
Authors: BURKHARDT DWIGHT A. , FAHEY PATRICK K. , SIKORA MICHAEL
Published: July 2002

The impulse discharge of single ganglion cells
was recorded extracellularly in superfused eyecup preparations
of the tiger salamander (Ambystoma tigrinum).
Contrast flashes (500 ms) were applied at the center of
the receptive field while the retina was light adapted
to a background field of 20 cd/m2. The incidence
of cell types in a sample of 387 cells was: ON cells (4%),
OFF cells (28%), and ON/OFF cells (68%). Quantitative contrast/response
measurements were obtained for 83 cells. On the basis of
C50, the contrast necessary to evoke a half-maximal response,
ON/OFF cells fell into 3 groups: (1) Positive Dominant
(26%), (2) Balanced (23%), and (3) Negative Dominant (51%).
Positive Dominant cells tended to be relatively contrast
insensitive. On the other hand, many Negative Dominant
cells showed remarkably low C50 values and very steep contrast/response
curves. Contrast gain to negative contrast averaged 8.5
impulses/s/% contrast, some four times greater than that
evoked by positive contrast. In most ON/OFF cells, the
latency of the first spike evoked by a negative contrast
step was much shorter (40–100 ms) than that evoked
by a positive contrast step of equal contrast. OFF cells
typically showed higher C50 values, larger dynamic ranges,
and longer latencies than those of Negative Dominant ON/OFF
cells. Thus, different pathways or mechanism apparently
mediate the off responses of OFF and ON/OFF cells. In sum,
the light-adapted retina of the tiger salamander is strongly
biased in favor of negative contrast, as shown by the remarkably
high contrast sensitivity and faster response of Negative
Dominant cells, the remarkably low incidence of ON cells,
and the insensitivity of Positive Dominant cells. Some
possible underlying influences of bipolar and amacrine
cells are discussed.
The selective impairment of the perception of first-order
motion by unilateral cortical brain damage
Authors: VAINA LUCIA M. , MAKRIS NIKOS , KENNEDY DAVID , COWEY ALAN
Published: July 2002

First-order (Fourier) motion consists of stable
spatiotemporal luminance variations. Second-order (non-Fourier)
motion consists instead of spatiotemporal modulation of
contrast, flicker, or spatial frequency. In spite of extensive
psychophysical and computational analysis of the nature
and relationship of these two types of motion, it remains
unclear whether they are detected by the same mechanism
or whether separate mechanisms are involved. Here we report
the selective impairment of first-order motion, on a range
of local and global motion tasks, in the contralateral
visual hemifield of a patient with unilateral brain damage
centered on putative visual areas V2 and V3 in the medial
part of the occipital lobe. His perception of second-order
motion was unimpaired. As his disorder is the obverse of
that reported after damage in the vicinity of human visual
area MT (V5), the results support models of motion processing
in which first- and second-order motion are, at least in
part, computed separately at the extrastriate cortical
level.
The thalamo-hyperstriatal system is established by the time
of hatching in chicks (Gallus gallus): A cholera
toxin B subunit study
Authors: WU CHI-CHENG , KARTEN HARVEY J.
Published: July 2002

Connections of the thalamo-hyperstriatal system
of hatchling chicks were investigated using multiple injections
of cholera toxin B subunit (CTb) in the wulst. In the diencephalon,
cells with CTb-like immunoreactivity (CTb-LI) were seen
bilaterally in n. dorsolateralis anterior thalami, pars
lateralis dorsalis and ventralis, n. dorsolateralis anterior
thalami, pars magnocellularis, and pars lateralis rostralis.
Within this complex, more CTb-LI cells were observed in
the ventral portions of the ipsilateral side, whereas more
labeled cells were found in the dorsolateral portions of
the contralateral side. Moreover, CTb-LI cells were seen
bilaterally in n. superficialis magnocellularis. In the
nonvisual thalamic structures, numerous CTb-LI cells were
seen in n. dorsolateralis anterior thalami, pars medialis
and n. dorsolateralis posterior thalami. In the ventral
thalamus, intense CTb-LI fibers/terminals were present
in the external half of the external laminae of n. geniculatus
lateralis, pars ventralis. Moderate to minor concentrations
of fibrous labeling were found in n. intercalatus thalami
and n. ventrolateral thalami. Moreover, efferent projections
of the wulst were evident in the most ventral half of the
optic tectum and the pretectal areas. The latter included
n. pretectalis medialis, n. spiriformis medialis, n. principalis
precommissuralis, n. lentiformis mesencephali, pars magnocellularis,
and n. superficialis synecephali. Also, CTb-LI fibers were
seen in n. basal optic root. The present study provides
strong evidence that neuronal connections of the thalamo-hyperstriatal
system are well established by the time of hatching. Additionally,
efferent projections from the wulst to the diencephalic,
mesencephalic, and pretectal structures are evident.
The ipsilateral retinal projection in the fat-tailed dunnart,
Sminthopsis crassicaudata
Authors: RODGER J. , DUNLOP S.A. , BEAZLEY L.D.
Published: July 2002

The population of retinal ganglion cells which
project ipsilaterally in the brain was examined in the
fat-tailed dunnart, Sminthopsis crassicaudata,
following injection of horseradish peroxidase into one
optic tract. Retinae were examined as wholemounts and optic
nerves as serial sections. In addition, visual fields were
measured ophthalmoscopically. Ipsilaterally projecting
ganglion cells were located temporal to a line which ran
vertically through the middle of the area centralis
and extended medially to define a ventrolateral crescent.
Temporal to the naso-temporal division, a mean of 77% of
ganglion cells projected ipsilaterally; these cells represented
20% of the total ganglion cell population. The magnitude
and retinal location of the ipsilateral projection correlated
with the extensive binocular field which measured 180 deg
in the vertical (from 20 deg below the horizontal axis
to 70 deg beyond the zenith) and 140 deg in horizontal
meridian. Ipsilaterally projecting axons were restricted
to the lateral third of the optic nerve along its length,
sharing territory with contralaterally projecting axons.
Distribution of GABA-like immunoreactive neurons and fibers
in the central visual nuclei and retina of frog, Rana
pipiens
Authors: LI ZHENG , FITE KATHERINE V.
Published: July 2002

Immunocytochemistry was used to study the distribution
of gamma-aminobutyric acid (GABA) throughout the central
visual nuclei and retina in Rana pipiens. In the
retina, GABA immunoreactivity (both somata and fibers)
was observed in all layers except the outer nuclear layer
(ONL). Contrary to earlier reports, about 30% of total
neurons within ganglion cell layer (GCL) expressed GABA
immunoreactivity. Double-labeling studies indicated that
about half of the GABA-containing perikarya in the GCL
were retinal ganglion cells (RGCs). In the diencephalon,
intensely labeled GABA-immunoreactive neurons and nerve
fibers were observed within the neuropil of Bellonci (nB)
and corpus geniculatum (CG), while only immunoreactive
puncta were found in the rostral visual nucleus (RVN).
In the pretectal region, the posterior thalamic nucleus
(nPT) contained the most intensely labeled GABA immunoreactive
perikarya and nerve fibers in the entire brain. Lightly
immunoreactive perikarya were also found in the large-celled
nucleus lentiformis mesencephali (nLM), as well as in the
pretectal gray, which contains neurons postsynaptic to
the retinal terminal zones within nLM. In the optic tectum
(OT), both immunoreactive perikarya and fibers were found
within superficial layers 8 and 9, whereas only densely
packed immunoreactive perikarya were evident in the deep
tectal layers (i.e. 2, 4, 6). The nucleus of the basal
optic root (nBOR) contained a small number of lightly labeled
GABA-immunoreactive perikarya, mostly located in the dorsal
half of the nucleus. A large number of perikarya within
the nucleus isthmi (NI) were also immunostained.
Response modulation by texture surround in primate area
V1: Correlates of “popout” under anesthesia
Authors: NOTHDURFT HANS-CHRISTOPH , GALLANT JACK L. , VAN ESSEN DAVID C.
Published: July 2002

We studied the effects of contextual modulation
in area V1 of anesthetized macaque monkeys. In 146 cells,
responses to a single line over the center of the receptive
field were compared with those to full texture patterns
in which the center line was surrounded by similar lines
at either the same orientation (uniform texture)
or the orthogonal orientation (orientation contrast).
On average, the responses to single lines were reduced
by 42% when texture was presented in the surround. Uniform
textures often produced stronger suppression (7% more,
on average) so that lines with orientation contrast on
average evoked larger responses than lines in uniform texture
fields. This difference is correlated with perceptual differences
between such stimuli, suggesting that physiological mechanisms
contributing to the saliency (“popout”) of
textural stimuli operate, at least to some degree, even
under anesthesia. Significant response modulation by the
texture surround was seen in 112 cells (77%). Fifty-three
cells (36%) responded differently to the two texture patterns;
response preferences for orientation contrast (35 cells;
24%) were seen more often than preferences for uniform
textures (18 cells; 12%). The remaining 59 cells (40%)
were similarly suppressed by both texture surrounds. Detailed
analysis of texture modulation revealed two major components
of surround effects: (1) fast nonspecific (“general”)
suppression that occurred at about the same latency as
excitatory responses and was found in all layers of striate
cortex; and (2) differential response modulation that began
about 60–70 ms after stimulus onset (about 15–20
ms after the onset of the excitatory response) and was
less homogeneously distributed over cortical layers.
Postnatal development of perisomatic GABAergic axon terminals
on neurons projecting from area 17 to area 18 of the cat
visual cortex
Authors: PÉREZ-CERDÁ FERNANDO , MARTÍNEZ-MILLÁN LUIS , MATUTE CARLOS
Published: July 2002

We have studied the postnatal development of presumptive
axon terminals (puncta) which were recognized by antibodies
to the inhibitory neurotransmitter gamma-aminobutyric acid
(GABA) and were located on the somata of area 17 neurons
projecting to the ipsilateral area 18 of the visual cortex
in cats ranging from 7 days of age to adulthood. Projection
neurons were retrogradely labeled by injection of horseradish
peroxidase conjugated to wheat germ agglutinin into the
ipsilateral area 18. These neurons were mainly pyramidal
in shape at all the developmental stages examined and the
adult distribution of labeled cells was reached by 21 days.
Subsequent GABA postembedding immunohistochemistry using
high-resolution light microscopy was carried out to study
the development of GABAergic terminals on cell bodies of
identified projecting neurons in layers II–III. At
all ages examined, we found perisomatic GABAergic puncta
on these cells. Their density showed a significant increase
from postnatal days 7 to 45, and then remained largely
constant through adulthood. Since GABAergic puncta are
considered the light-microscopic correlate of GABAergic
synaptic terminals, our results support the idea of a developmentally
regulated increase in the inhibitory activity of local
interneurons on area 17 pyramidal neurons projecting to
area 18 in the cat visual cortex which occurs within the
same time frame as that of the acquisition of the mature
operation of these cells.
Spatiotemporal structure of depolarization spread in cortical
pyramidal cell populations evoked by diffuse retinal light
flashes
Authors: SENSEMAN DAVID M.
Published: July 2002

The spatiotemporal structure of cortical activity
evoked by diffuse light flashes was investigated in an
isolated eyecup-brain preparation of the pond turtle, Pseudemys
scripta. By combining a photomicroscopic image of
the preparation with voltage-sensitive dye signals recorded
by a 464-element photodiode array, the spread of depolarization
within different cortical areas could be directly visualized
with millisecond temporal resolution. Diffuse stimulation
of the contralateral eyecup initially depolarized the visual
cortex at the junction between its lateral and medial divisions
in a small area rostral of the ventricular eminence. From
this point, the depolarization spread at different velocities
(10–100 μm/ms) depending upon the direction of
travel. Since the initial depolarization was always in
the rostral pole, the largest spread invariably occurred
in a rostral → caudal direction. Within the confines
of the medial visual cortex, depolarization spread at a
constant velocity but slowed after entering the adjoining
medial cortex. Increasing the stimulus illuminance increased
the velocity of spread. Rostrocaudal spread of depolarization
was also observed in response to electrical stimulation
of the geniculocortical pathway and by direct focal stimulation
of the cortical sheet. These data suggest that excitatory
connections between pyramidal cell clusters play a prominent
role in the initial activation of the cortex by diffuse
retinal stimulation.
Excitatory amino acid-induced inositol phosphate formation
in cultured retinal pigment epithelium
Authors: FRAGOSO GABRIELA , LÓPEZ-COLOMÉ ANA MARÍA
Published: July 2002

Excitatory amino acid (EAA)-induced production
of inositolphosphates (IPs) was studied in primary cultures
of chick retinal pigment epithelium (RPE) following in
vitro incorporation of [3H] myo-inositol.
Glutamic acid (L-glu) significantly increased [3H]-IPs
accumulation (215%). L-glu agonists stimulated [3H]IPs
accumulation in the following order of efficiency: N-methyl-D-aspartate
(NMDA) ≥ L-glu > quisqualate ≥ kainate > (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic
acid (ACPD). Stimulation was dependent on external Ca2+.
The NMDA-induced response was blocked by (+)-5-methyl-10,11-dihydro-5H-dibenzo-cyclohepten-5,10-imine
maleate (MK-801) and 3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic
acid (CPP) and was decreased by the L-Ca2+-channel
blockers verapamil and nifedipine as well as by dantrolene.
The metabotropic glutamate receptor (mGluR) antagonist
(+)-α-methyl-4-carboxyphenylglycine (+)MCPG inhibited
3,5-dihydroxyphenylglycine (DHPG) and ACPD-induced stimulation,
which demonstrates the presence in RPE of mGluRs 1 and/or
5, as well as NMDA receptors coupled directly, or through
the influx of external Ca2+, to phospholipase
C activation. L-glu agonists showed no effect either on
basal level of intracellular cyclic adenosine monophosphate,
nor on forskolin- or carbachol-induced stimulation of adenylyl
cyclase. Since L-glu is released from the retina upon illumination,
and receptors for this compound are present in RPE, the
activation of the inositide pathway could be involved in
the regulation of retina-RPE interaction, which is essential
for the visual process.
Neurogenesis in the visual system of embryonic and adult
zebrafish (Danio rerio)
Authors: MARCUS RIVA C. , DELANEY CATHERINE L. , EASTER STEPHEN S.
Published: July 2002

The zebrafish has recently assumed a central position
in the study of vertebrate development. Numerous studies
of other fish have shown that their central nervous systems,
and especially their visual systems, continue to add new
neurons throughout life, which is probably related to their
abilities to regenerate axons and whole nervous tissue.
Retinal neurogenesis had not been examined in adult zebrafish,
and two reports concluded that the optic tectum ceased
neurogenesis early in life, so the question arose whether
the zebrafish was anomalous in this regard. We labeled
embryonic (24- and 48-h postfertilization) and adult zebrafish
with the thymidine analog, bromo-deoxyuridine, and, after
short and long survivals, examined the retina and brain
for labeled cells. They were abundant in both the optic
tectum and the retina. Although the rate of retinal growth
slows considerably between embryonic and adult stages,
the patterns of neurogenesis in both the embryo and the
adult are similar to those described in other fish, so
these “fish-specific” features of general interest
can justifiably be studied in zebrafish.
Projections of single retinal ganglion cells to the visual
centers: An intracellular staining study in a plethodontid
salamander
Authors: WIGGERS WOLFGANG
Published: July 2002

The projection specificity of retinal ganglion
cells and the morphology of their terminals were studied
in the plethodontid salamander Plethodon jordani.
In an in vitro approach, ganglion cells were stained
with biocytin and reconstructed by means of light microscopy.
Single retinal ganglion cells often have multiple terminal
structures in the thalamus, pretectum, and tectum. The
projection pattern in the diencephalic neuropils is related
to the depth of the terminal arbor within the tectal fiber
layer. Terminal arbors in the tectum differ in location,
size, and branching pattern. The following types could
be distinguished: The most superficial of the
optic terminals in layer 1 are relatively small with a
diameter of about 100 μm. With the exception of a few
varicosities (beads) in the pretectal neuropils, their
stem axons have no further collaterals or terminal arbors
in the diencephalic neuropils. Intermediate terminals
in layer 2 fan out to form a dense plexus with a medio-lateral
extent of 180 μm on average. Some terminals in this
layer show obvious antenna-like fibers reaching toward
the surface of the tectum. The axons of layer 2 projecting
neurons have additional collaterals and terminal arbors
in the thalamus and pretectum. The deep layer
3 terminals spread out over a diameter of 400 μm on
average and their degree of branching is moderate. The
axons of layer 3 projecting ganglion cells have dense additional
terminal arbors in the thalamus and pretectum. The deepest
retinal terminals in the tectum are found within the predominantly
efferent fiber layers. This type consists of an unbranched,
but beaded axon which runs rostro-caudally with several
bends and loops. The stem axon has an additional very dense
terminal arborization in the neuropil of the nucleus Bellonci
pars medialis and additional sparse collaterals in the
pretectal area.
Immunocytochemical localization of excitatory and inhibitory
neurotransmitters in the zebrafish retina
Authors: CONNAUGHTON V.P. , BEHAR T.N. , LIU W.-L.S. , MASSEY S.C.
Published: July 2002

The patterns of glutamate, γ-aminobutyric acid
(GABA), and glycine distribution in the zebrafish retina
were determined using immunocytochemical localization of
antisera at the light-microscope level. The observed GABA
immunoreactivity (GABA-IR) patterns were further characterized
using antibodies to both isoforms of glutamic acid decarboxylase
(GAD65 and GAD67), the synthetic
enzyme for GABA. Glutamate-IR was observed in all retinal
layers with photoreceptors, bipolar cells, and ganglion
cells prominently labeled. Bipolar cells displayed the
most intense glutamate-IR and bipolar cell axon terminals
were clearly identified as puncta arranged in layers throughout
the inner plexiform layer (IPL). These findings suggest
the presence of multiple subtypes of presumed OFF- and
ON-bipolar cells, including some ON-bipolar cells characterized
by a single, large (9 μm × 6 μm) axon terminal.
GABA-, GAD-, and glycine-IR were most intense in the inner
retina. In general, the observed labeling patterns for
GABA, GAD65, and GAD67 were similar.
GABA- and GAD-IR were observed in a population of amacrine
cells, a few cells in the ganglion cell layer, throughout
the IPL, and in horizontal cells. In the IPL, both GABA-
and GAD-IR structures were organized into two broad bands.
Glycine-IR was observed in amacrine cells, interplexiform
cells, and in both plexiform layers. Glycine-positive terminals
were identified throughout the IPL, with a prominent band
in sublamina 3 corresponding to an immunonegative region
observed in sections stained for GAD and GABA. Our results
show the distribution of neurons in the zebrafish retina
that use glutamate, GABA, or glycine as their neurotransmitter.
The observed distribution of neurotransmitters in the inner
retina is consistent with previous studies of other vertebrates
and suggests that the advantages of zebrafish for developmental
studies may be exploited for retinal studies.
Cooperative and competitive spatial interactions in motion
integration
Authors: LORENCEAU JEAN , ZAGO LAURE
Published: July 2002

Recovering the velocity of objects moving in the
visual field requires both the integration and segmentation
of local neuronal responses elicited by moving stimuli
in primary visual cortex. Herein, we investigate the effects
of the contrast, density, spatial proximity, spatial frequency,
and spatial configuration of component motions on these
complementary processes. Measuring the ability of human
observers to discriminate the global direction of motion
displays composed of spatially distributed patches of drifting
gratings whose motion is locally ambiguous, we provide
psychophysical evidence that linking component motion across
space is facilitated at low contrast and high patch density.
Furthermore, direction discrimination depends on the spatial
frequency of component gratings and is more accurate for
spatial configurations that contain “virtual”
L junctions as compared to configurations composed of “virtual”
T junctions. We suggest that the conditions yielding global
motion coherence can be accounted for by the existence
of anisotropic cooperative/competitive, contrast-dependent,
long-range interactions among oriented direction-selective
units. In addition, we bring evidence that motion segmentation
processes rely upon the processing of moving local spatial
discontinuities. The results are discussed in the light
of recent psychophysical and physiological evidence that
long-range excitatory and inhibitory interactions within
primary visual cortex modulate perceptual linking.
AMPA receptor kinetics limit retinal amacrine cell excitatory
synaptic responses
Authors: TRAN MY N. , HIGGS MATTHEW H. , LUKASIEWICZ PETER D.
Published: July 2002

Amacrine cells that respond transiently to maintained
illumination are thought to mediate transient inhibitory
input to ganglion cells. The excitation of these transient
amacrine cells is thought to be limited by inhibitory feedback
to bipolar cells. We investigated the possibility that
desensitizing AMPA and/or kainate (KA) receptors on amacrine
cells might also limit the duration of amacrine cell excitation.
To determine how these receptors might affect amacrine
cell input and output, we made whole-cell recordings from
amacrine and ganglion cells in the salamander retinal slice.
The specific AMPA receptor antagonist GYKI-53655 blocked
non-NMDA receptor-mediated amacrine cell excitatory postsynaptic
currents (EPSCs) and kainate puff-elicited currents, indicating
that AMPA, and not KA, receptors mediated the responses.
Cyclothiazide, an agent that reduces AMPA receptor desensitization,
increased the amplitude and duration of amacrine cell EPSCs.
To measure the output of transient amacrine cells, we recorded
glycinergic inhibitory postsynaptic currents (IPSCs) from
ganglion cells, and found that these were also enhanced
by cyclothiazide. Thus, prolongation of amacrine cell AMPA
receptor activation enhanced amacrine cell output. Current
responses elicited by puffing glycine onto ganglion cell
dendrites were not affected by cyclothiazide, indicating
that the enhancement of glycinergic IPSCs was not due to
a direct effect on glycine receptors. These data suggest
that rapid AMPA receptor desensitization and/or deactivation
limits glycinergic amacrine cell excitation and the resulting
inhibitory synaptic output.
Human symmetry detection exhibits reverse eccentricity scaling
Authors: TYLER CHRISTOPHER W.
Published: July 2002

Human symmetry detection in dense patterns exhibits
a spatial integration range that becomes narrower with
distance of the symmetry axis from the fovea. This narrowing
violates the general properties of eccentricity that have
been found for all previous visual cortical areas, tasks,
and assessment techniques. This reverse eccentricity scaling
may, in conjunction with the long-range matching properties
for symmetry described in Tyler and Hardage (1996), imply
that symmetry is processed by a specialized cortical area
with non-retinotopic neural architecture.
Midget and parasol ganglion cells of the primate retina
express the α1 subunit of the glycine receptor
Authors: GRÜNERT ULRIKE , GHOSH KRISHNA K.
Published: July 2002

Glycine is a major inhibitory neurotransmitter
in the mammalian retina and has been shown to influence
the responses of ganglion cells. Midget and parasol ganglion
cells serve distinct physiological roles in the primate
retina and show differences in their response characteristics
to light stimuli. In the present study, we addressed the
question of whether the expression of glycine receptors
differs in midget and parasol ganglion cells. Ganglion
cells in the retinae of marmoset and macaque monkeys were
injected with Neurobiotin in a live in vitro retinal
whole-mount preparation. Retinal pieces were then processed
with an antibody against the α1 subunit of the glycine
receptor. Strong punctate immunoreactivity indicative of
synaptic localization is present in the ON and OFF sublamina
of the inner plexiform layer. Many of the immunoreactive
puncta coincide with the dendrites of both midget and parasol
ganglion cells. Immunoreactive puncta are present on distal
and proximal dendrites of ON and OFF cells. These results
suggest that ON and OFF midget and parasol cells do not
differ with respect to the distribution of the α1 subunit
of the glycine receptor.
Developmental traumatology: The psychobiological development of maltreated children and
its implications for research, treatment, and policy
Authors: DE BELLIS MICHAEL D.
Published: July 2002

In this review, a developmental traumatology model of child maltreatment and the risk for the
intergenerational cycle of abuse and neglect using a mental health or posttraumatic stress model
was described. Published data were reviewed that support the hypothesis that the
psychobiological sequelae of child maltreatment may be regarded as an environmentally
induced complex developmental disorder. Data to support this view, including the
descriptions of both psychobiological and brain maturation studies in maltreatment research,
emphasizing the similarities and differences between children, adolescents, and adults, were
reviewed. Many suggestions for important future psychobiological and brain maturation research
investigations as well as public policy ideas were offered.