bluuebunny/crossref_metadata_2025 huggingface dataset:
Membrane current of retinal rods of Caudiverbera
caudiverbera (Amphibia: Leptodactylidae): Dark noise, spectral
and absolute light sensitivity
Authors: PALMA FRANCISCO , RONCAGLIOLO PABLO , BACIGALUPO JUAN , PALACIOS ADRIÁN G.
Published: December 2002

We investigated the photocurrents from isolated rods of the
South American anuran, Caudiverbera caudiverbera. Rod
outer segments were on average 66.4 ± 11.2 μm (mean
± S.D., n = 104) in length and 6.6 ±
0.9 μm (mean ± S.D.) in diameter; 40 ± 22
photoisomerizations (mean ± S.D., range 10–99,
n = 16) were required for eliciting a half-saturating
photocurrent response. The time-to-peak was 911 ± 217
ms (mean ± S.D., n = 14, 20°C) in the linear
range of the response and the integration time of the current
response was 1744 ± 451 ms (mean ± S.D., n
= 14). The time-to-peak appears to be slower and the integration
time shorter in Caudiverbera than in Ambystoma
tigrinum, Rana pipiens or Xenopus laevis
rods under similar experimental conditions. The α-band of
rod spectral sensitivity has a λmax at
520 ± 2.1 nm (mean ± S.D., range 516–525 nm,
n = 24) and the bandwidth fits a porphyropsin visual pigment.
The single-event response amplitude ranges from 0.31–0.51 pA,
depending on the calculation method. The intrinsic dark current
(variance at dark minus variance under bright light) was 0.045 ±
0.040 pA2 (mean ± S.D., n = 24). Our results
support the presence of a dark-noise component below 1 Hz, with kinetics
similar to the single-photon evoked response and a rate of 0.006 events
s−1 (n = 9).
Rabbit cone bipolar cells: Correlation of their morphologies
with whole-cell recordings
Authors: McGILLEM GREGORY S. , DACHEUX RAMON F.
Published: December 2002

The superfused retinal slice preparation was used to examine
the morphology and glutamate-activated whole-cell currents of
rabbit bipolar cells. There were six morphologically distinct
types of cone bipolar cells and a rod bipolar cell that had
axon terminals stratifying in stratum 3 to 5 of
sublamina-b. All of these bipolar cell types exhibited
an outward current in response to the application of the
metabotropic glutamate receptor, mGluR6, agonist AP-4 (APB),
and had I/V curves indicative of membrane channel closure.
Conversely, there were no currents activated during the application
of kainate, the AMPA/kainate receptor agonist. These data
demonstrate they were on-bipolar cells. In addition, there were
six morphologically distinct cone bipolar cells that stratified
in sublamina-a. Every cell with axonal arborizations
in stratum 1 and 2 exhibited an inward current when the ionotropic
glutamate receptor agonist kainate was applied. This current
was blocked by application of the AMPA/kainate receptor antagonist
CNQX. These cells also decreased their membrane resistance in
response to kainate, a characteristic of the opening of channels
within the plasma membrane. Without exception, no cells stratifying
in sublamina-a responded to the mGluR6 agonist AP-4,
further identifying them as off-bipolar cells.
Lateral spread of adaptation as measured with the multifocal
electroretinogram
Authors: SEIPLE WILLIAM , VAJARANANT THASARAT S. , PEPPERBERG DAVID R. , SZLYK JANET P.
Published: December 2002

We examined whether lateral spread of adaptation can be observed
in the electroretinogram in humans. Specifically, we tested
whether the luminance level of a surrounding, nonmodulated annulus
affects the multifocal electroretinogram (ERG) response of a
modulated central area. Multifocal electroretinograms were recorded
in response to an array of 37 unscaled hexagons subtending a
retinal area of 38 deg × 35 deg. Responses were recorded
in six control subjects. In the first series of experiments,
only the center hexagon was modulated, while the surrounding
36 hexagons were held constant at either 0.45, 172, or 340
cd/m2. In a subsequent series of control experiments,
modulation depth of the center hexagon was varied and the proximity
of the surrounding hexagon systematically altered. For the
center-modulated condition, response amplitude and implicit time for
the first-order kernel response significantly decreased as a function
of increasing surround luminance. Control experiments demonstrated that
the effect of the surround illumination was not due to scattered
light but was influenced by the proximity of the surrounding
annulus. These results demonstrate that lateral adaptation
influences can be measured using the multifocal ERG.
Multiple cell targets for melatonin action in Xenopus
laevis retina: Distribution of melatonin receptor
immunoreactivity
Authors: WIECHMANN ALLAN F. , WIRSIG-WIECHMANN CELESTE R.
Published: December 2002

In the retina of the African clawed frog (Xenopus
laevis), melatonin is synthesized by the photoreceptors
at night, and binds to receptors that likely mediate paracrine
responses. Melatonin appears to alter the sensitivity of the
retinal cells to light, and may play a key role in regulating
important circadian events that occur in the eye. A polyclonal
antibody was raised against a 13 amino acid peptide corresponding
to a region of the third cytoplasmic loop of the Xenopus
laevis Mel1c melatonin receptor. Western blot
analysis revealed a major immunoreactive band of approximately
60 kD in neural retina and retinal pigment epithelium (RPE)
membranes. Immunocytochemical labeling of sections of
Xenopus eyes demonstrated intense melatonin receptor-like
immunoreactivity in the inner plexiform layer (IPL). Immunolabeling
with antibodies to glutamate decarboxylase (GAD) or tyrosine
hydroxylase (TOH) appeared to co-localize with the melatonin
receptor immunoreactivity in different sublaminas of the IPL.
This suggests that both GABAergic and dopaminergic amacrine
cells express melatonin receptor protein. There were also some
melatonin receptor immunoreactive varicose fibers in the IPL
that did not co-localize with either TOH or GAD, and may represent
efferent fibers, since they could be followed into the optic
nerve. Melatonin receptor immunoreactivity was also present
on cell soma in the ganglion cell layer. Furthermore, a moderate
level of melatonin receptor immunoreactivity was observed in
the RPE and rod and cone photoreceptor cells. The presence of
melatonin receptor immunoreactivity in these cells supports
previous observations of melatonin receptor RNA expression in
multiple cell types in the Xenopus retina. Expression
of melatonin receptor protein in the photoreceptors suggests
that melatonin may have a direct action on these cells.
AMPA-preferring receptors mediate excitatory non-NMDA responses
of primate retinal ganglion cells
Authors: JACOBY ROY A. , WU SAMUEL M.
Published: December 2002

Glutamate and kainate-induced currents of primate ganglion
cells were studied using the whole-cell patch-clamp technique
in a retinal slice preparation. Antagonists and allosteric
modulators of desensitization selective for either
α-amino-3-hydroxy-5-methyl-4-isoazoleprionic acid (AMPA)-
or kainate-preferring receptors were used to determine the
contributions of each type of receptor to excitatory responses.
With synaptic transmission and NMDA receptors blocked, the
AMPA-preferring receptor antagonist GYKI 52466 (30 μM–100
μM) reversibly blocked most of the glutamate-induced current
in ganglion cells. GYKI 52466 also blocked the response in ganglion
cells to focally applied kainate, suggesting that the current
response to kainate arises from activation of AMPA-preferring
receptors, and not kainate-preferring receptors. Both cyclothiazide
(10 μM–100 μM) and the novel drug
4-[2-(phenylsulfonylamino)ethylthio]-2,6-difluoro-phenoxyacetamide
(PEPA, 20 μM–100 μM), which selectively enhance
responses mediated by AMPA-preferring receptors, enhanced
glutamate-induced responses of ganglion cells. Since these drugs
preferentially inhibit desensitization of the flip and flop
splice variants, respectively, of AMPA-preferring receptors,
it is likely that both splice variants are present on these
ganglion cells. Concanavalin A, which selectively suppresses
the desensitization of kainate-preferring receptors, had no
effect on the glutamate-induced responses of ganglion cells.
We conclude that the non-NMDA component of the excitatory,
glutamatergic input to primate ganglion cells is mediated largely
by AMPA-preferring receptors, with little, if any,
kainate-preferring receptor-mediated response.
Retinal development of West Australian dhufish, Glaucosoma
hebraicum
Authors: SHAND JULIA , ARCHER MICHAEL A. , THOMAS NICOLE , CLEARY JENNIFER
Published: December 2002

An investigation of retinal specializations was carried out
in larval and juvenile dhufish, Glaucosoma hebraicum
(Glaucosomidae, Teleostei). The development of photoreceptors
and formation of the retinal mosaic was followed by light and
electron microscopy. At hatching the eye was undifferentiated.
Cone photoreceptors were present by day 3 posthatch (dph), when
exogenous feeding began. Single and multiple cones were present
in a row arrangement from 3 dph to 20 dph, when the first rod
nuclei were observed. Between 20 dph and approximately 3 months
posthatch (mph), the row arrangement was replaced by a square
mosaic of four double cones surrounding a single cone, and the
cones increased in size, with the outer segments reaching up
to 30 μm in length. During the period of spatial rearrangement,
triple cones were often observed. From their first appearance,
rod photoreceptors were added rapidly. Investigation of ganglion
cell topography in 3-mph fish that had attained the adult-like
square photoreceptor mosaic was carried out using retinal
wholemounts. The highest densities of neurones in the ganglion
cell layer were in temporal retina but no well-defined area
centralis was observed. Microspectrophotometric measurements
of the visual pigments within the outer segments of the
photoreceptors of 3-mph fish revealed double cones with identical
absorption spectra in each member of the outer segment, and
the wavelength of maximum absorption (λmax) located
at 522 nm. Single cones were found to possess a visual pigment
with λmax at 460 nm and rods with a
λmax of 498 nm. The results imply that the larvae
and juveniles are adapted for survival in coastal waters and
may be active in relatively low light levels from early stages
of development.
Cortical and subcortical afferents to the nucleus reticularis
tegmenti pontis and basal pontine nuclei in the macaque monkey
Authors: GIOLLI ROLAND A. , GREGORY KENNETH M. , SUZUKI DAVID A. , BLANKS ROBERT H.I. , LUI FAUSTA , BETELAK KATHLEEN F.
Published: December 2002

Anatomical findings are presented that identify cortical and
subcortical sources of afferents to the nucleus reticularis
tegmenti pontis (NRTP) and basal pontine nuclei. Projections
from the middle temporal visual area (MT), medial superior temporal
visual area (MST), lateral intraparietal area (LIP), and areas
7a and 7b to the basal pontine nuclei were studied using
3H-leucine autoradiography. The results complemented a
parallel study of retrograde neuronal labeling attributable to
injecting WGA-HRP into NRTP and neighboring pontine nuclei. Small
3H-leucine injections confined to MT, MST, LIP, area
7a, or area 7b, produced multiple patches of pontine terminal
label distributed as follows: (1) An injection within
MT produced terminal label limited to the dorsolateral and lateral
pontine nuclei. (2) Injections restricted to MST or
LIP showed patches of terminal label in the dorsal, dorsolateral,
lateral, and peduncular pontine nuclei. (3) Area 7a
targets the dorsal, dorsolateral, lateral, peduncular, and ventral
pontine nuclei, whereas area 7b projects, additionally, to the
dorsomedial and paramedian pontine nuclei. Notably, no projections
were seen to NRTP from any of these cortical areas. In contrast,
injections made by other investigators into cortical areas anterior
to the central sulcus revealed cerebrocortical afferents to
NRTP, in addition to nuclei of the basal pontine gray. With
our pontine WGA-HRP injections, retrograde neuronal labeling
was observed over a large extent of the frontal cortex continuing
onto the medial surface which included the lining of the cingulate
sulcus and cingulate gyrus. Significant subcortical sources
for afferents to the NRTP and basal pontine nuclei were the
zona incerta, ventral mesencephalic tegmentum, dorsomedial
hypothalamic area, rostral interstitial nucleus of the medial
longitudinal fasciculus, red nucleus, and subthalamic nucleus.
The combined anterograde and retrograde labeling data indicated
that visuo-motor cortico-pontine pathways arising from parietal
cortices target only the basal pontine gray, whereas the NRTP,
together with select pontine nuclei, is a recipient of afferents
from frontal cortical areas. The present findings implicate
the existence of parallel direct and indirect cortico-pontine
pathways from frontal motor-related cortices to NRTP and
neighboring pontine nuclei.
Photoreceptors and visual pigments in the red-eared turtle,
Trachemys scripta elegans
Authors: LOEW E.R. , GOVARDOVSKII V.I.
Published: December 2002

Absorbance spectra of cone outer segments and oil droplets
were recorded microspectrophotometrically in the retina of the
red-eared turtle, Trachemys scripta elegans. There
are four cone visual pigments, with λmax = 617
nm (red sensitive), 515 nm (green sensitive), 458 nm (blue
sensitive), and 372 nm (UV-sensitive). The red-sensitive pigment
resides in single cones with red or orange oil droplets, and
in both members of double cones. The principal member of the
double cone contains an orange oil droplet, and the accessory
member is droplet free. The green-sensitive pigment is situated
in single cones with orange/dark yellow droplets. The
blue-sensitive pigment is combined with the UV-absorbing oil
droplet in single cones. The UV-sensitive pigment resides in
single cones with clear oil droplets that exhibited virtually
no absorbance down to 325 nm. Thus, seven types of cones can
be identified based on their morphology, oil droplet color,
and the visual pigment absorbance. At the moment, this is the
most complex cone system described for vertebrates.
Tetrachromatic input to turtle horizontal cells
Authors: ZANA Y. , VENTURA D.F. , de SOUZA J.M. , DeVOE R.D.
Published: December 2002

Recent physiological experiments support behavioral and
morphological evidence for a fourth type of cone in the turtle
retina, maximally sensitive in the ultraviolet (UV). This cone
type has not yet been included in the models proposed for
connectivity between cones and horizontal cells. In this study,
we examined the inputs of UV, S, M, and L cones to horizontal
cells. We used the high-resolution Dynamic Constant Response
Method to measure the spectral sensitivity of horizontal cells
without background light and after adaptation to UV, blue (B),
green (G), and red (R) light. We concluded the following: (1)
Tetrachromatic input to a Y/B horizontal cell was identified.
The spectral-sensitivity curves of the cell in three of the
adaptation conditions were well represented by L-, M-, and S-cone
functions. Adaptation to blue light revealed a peak at 372 nm,
the same wavelength location as that determined behaviorally
in the turtle. A porphyropsin template could be closely fitted
to the sensitivity band in that region, strong evidence for
input from a UV cone. (2) The spectral-sensitivity functions
of R/G horizontal cells were well represented by the L- and
M-cone functions. There was no indication of UV- or S-cone inputs
into these cells. (3) The spectral sensitivities of the monophasic
horizontal cells were dominated by the L cone. However, the
shape of the spectral-sensitivity function depended on the
background wavelength, indicating secondary M-cone input.
Connectivity models of the outer retina that predict input from
all cone types are supported by the finding of tetrachromatic
input into Y/B horizontal cells. In contrast, we did not find
tetrachromatic input to R/G and monophasic horizontal cells.
Chromatic adaptation revealed the spectral-sensitivity function
of the turtle UV cone peaking at 372 nm.
Alterations in NMDA receptor expression during retinal
degeneration in the RCS rat
Authors: GRÜNDER TATIANA , KOHLER KONRAD , GUENTHER ELKE
Published: December 2002

To determine how a progressive loss of photoreceptor cells
and the concomitant loss of glutamatergic input to second-order
neurons can affect inner-retinal signaling, glutamate receptor
expression was analyzed in the Royal College of Surgeons (RCS)
rat, an animal model of retinitis pigmentosa. Immunohistochemistry
was performed on retinal sections of RCS rats and congenic controls
between postnatal (P) day 3 and the aged adult (up to P350)
using specific antibodies against N-methyl-D-aspartate (NMDA)
subunits. All NMDA subunits (NR1, NR2A–2D) were expressed
in control and dystrophic retinas at all ages, and distinct
patterns of labeling were found in horizontal cells, subpopulations
of amacrine cells and ganglion cells, as well as in the outer
and inner plexiform layer (IPL). NR1 immunoreactivity in the
inner plexiform layer of adult control retinas was concentrated
in two distinct bands, indicating a synaptic localization of
NMDA receptors in the OFF and ON signal pathways. In the RCS
retina, these bands of NR1 immunoreactivity in the IPL were
much weaker in animals older than P40. In parallel, NR2B
immunoreactivity in the outer plexiform layer (OPL) of RCS rats
was always reduced compared to controls and vanished between
P40 and P120. The most striking alteration observed in the
degenerating retina, however, was a strong expression of NR1
immunoreactivity in Müller cell processes in the inner
retina which was not observed in control animals and which was
present prior to any visible sign of photoreceptor degeneration.
The results suggest functional changes in glutamatergic receptor
signaling in the dystrophic retina and a possible involvement
of Müller cells in early processes of this disease.
Diurnal variation in synaptic ribbon length and visual threshold
Authors: BALKEMA GRANT W. , CUSICK KATHLEEN , NGUYEN TRI-HUNG
Published: December 2002

Previous work suggests that photoreceptor synaptic ribbon length
and absolute dark-adapted threshold may vary during a 24-h diurnal
cycle. To test this hypothesis, we examined the length of
photoreceptor synaptic ribbons and the dark-adapted threshold
in black (+/+) and albino (c2J/c2J) C57BL/6J
mice at six times over a 24-h period. Testing began 2 h after
light onset (ZT 2:00) and continued at successive 4-h intervals
(12 h:12 h light:dark). We determined the length of the synaptic
ribbons in frozen sections by labeling them with an antibody
specific for synaptic ribbons. Synaptic ribbons vary in length
at different points in the diurnal cycle in both types of mice,
but the synaptic ribbons in black mice are longer than those
in albino mice by an average of 0.33 μm. The synaptic ribbons
of black mice also have a larger response to changes in the
light cycle. Ribbon length in black mice ranges from 1.66 μm
to 1.4 μm, whereas ribbon length in albino mice ranges from
1.32 μm to 1.25 μm. The shortest ribbons are evident
6 h after light onset in both types of mice, whereas the longest
ribbons appear within 2 h after light onset. These changes in
synaptic ribbon length support the idea that photoreceptor synaptic
ribbons are dynamic structures whose length changes over a 24-h
diurnal cycle. Examining black and albino mice with a water-maze
behavioral assay showed that visual thresholds in black and
albino mice vary over the 24-h diurnal cycle. The visual thresholds
of albino mice are elevated compared with black mice at all
times tested. This is consistent with previous findings of visual
thresholds in hypopigmented mice. The lowest threshold (greatest
sensitivity) is present 2 h after light onset (ZT 2:00) and
corresponds to the time when synaptic ribbons are the longest.
The highest threshold is observed 6 h after light onset, the
time when synaptic ribbons are shortest. These results show
that synaptic ribbon length and visual sensitivity vary together
in relation to the time.
Voltage-gated calcium and sodium currents of starburst amacrine
cells in the rabbit retina
Authors: COHEN ETHAN D.
Published: December 2002

The voltage-gated calcium and sodium currents of starburst
amacrine cells were examined in slices of the adult rabbit retina.
ON-center starburst amacrine cells were targeted for whole-cell
recording by prelabeling the retina with the nuclear dye
4′-6-diamidino-2-phenylindole hydrochloride (DAPI). Calcium
currents were isolated using an external Ringer that contained
tetrodotoxin to block sodium currents and barium to block potassium
channels. When starburst amacrine cells were stepped to holding
potentials positive to −50 mV, a series of voltage-dependent
calcium currents were activated. The calcium current peaked
at −10 mV. The calcium currents kinetics were mainly
sustained in nature, showing only a small amount of slow
inactivation. Nickel (100 μM), a T-type channel blocker,
had no effect on the calcium current. Application of the L-type
channel agonist BAY K8644 (1–2.5 μM) had small variable
effects on the calcium current while the L-type channel antagonist
nifedipine (10 μM) had no effect. However, addition of a
reported N-type calcium channel antagonist, omega-conotoxin
G6A (1 μM), blocked a large portion of the calcium current,
as did a more nonselective antagonist, omega-conotoxin M7C (200
nM). Agatoxin 4A (500 nM) reduced a smaller sustained calcium
current component, implying a P/Q-type calcium channel was present
on these neurons. In addition to the calcium currents, a fast
voltage-gated sodium current was observed in many starburst
cells. This current could be blocked by tetrodotoxin (200–500
nM). The differing kinetics and durations of the sodium and
calcium currents could play important roles in the regulation
of synaptic release and in the coordination of spiking by starburst
amacrine cell dendrites during retinal development and in the
encoding of motion across the retinal surface.
Layer differences in the effect of monocular vision in light-
and dark-reared kittens
Authors: BEAVER CHRISTOPHER J. , JI QINGHUA , DAW NIGEL W.
Published: December 2002

We compared the effect of 2 days of monocular vision on the
ocular dominance of cells in the visual cortex of light-reared
kittens with the effect in dark-reared kittens at 6, 9, and
14 weeks of age, and analyzed the results by layer. The size
of the ocular-dominance shift declined with age in all layers
in light-reared animals. There was not a large change in the
ocular-dominance shift with age in dark-reared animals in any
layer, suggesting that dark rearing largely keeps the cortex
in the immature 6-week state until 14 weeks or longer, although
there was a slight decrease in layers II, III, and IV, and a
slight increase in layers V and VI. At 14 weeks, the difference
between light- and dark-reared animals was smallest in layer
IV, larger in layers II/III, and largest in layers V/VI, suggesting
that dark rearing has a large effect on intracortical synapses
and a small effect on geniculocortical synapses. There was a
significant ocular-dominance shift in layer IV at 14 weeks of
age in both light- animals and dark-reared animals, showing
that the critical period for ocular-dominance plasticity is
not ended at this age. While the ocular-dominance shift after
26 h of monocular deprivation in 6-week animals was similar
in light- and dark-reared animals, after 14 h it was smaller
in dark-reared animals, showing that ocular-dominance changes
occur more slowly in dark-reared animals at this age, in agreement
with Mower (1991). Increases in selectivity for axis of movement
after 26 h of monocular vision were seen in dark-reared animals
at 6 weeks of age, but not at 9 or 14 weeks of age, showing
that the critical period for axial selectivity ends earlier
than the critical period for ocular dominance in dark-reared
animals, as it does in light-reared animals.
Effects of monocular deprivation and reverse suture on
orientation maps can be explained by activity-instructed
development of geniculocortical connections
Authors: MILLER KENNETH D. , ERWIN ED
Published: December 2002

Mature visual cortex shows a single, binocularly matched
orientation map. This matching develops without visual experience.
It persists despite early monocular deprivation that largely
eliminates one eye's map, followed by reverse suture
(deprivation of the previously open eye and opening of the
previously deprived eye), even though the two eyes lack common
visual experience in this case. These results have been interpreted
to suggest that the structure of orientation maps either is
innately predetermined or, if it arises through self-organization,
is determined by external cues such as boundary conditions or
a “scaffolding” of horizontal connections. We show,
to the contrary, that these results are the expected outcomes
if orientation maps develop through activity-instructed,
correlation-based development of the geniculocortical connections
without additional cues. A weak, binocularly correlated orientation
map is known to exist before deprivation onset; we previously
showed how this can arise through activity-instructed development.
Now we show that this initial correlation between the two
eyes' maps can persist or increase despite deprivation
sufficient to cause massive loss of the deprived eye's
geniculocortical synaptic strength, followed by reverse suture.
Given sufficient early correlated map development, each map's
fate is “dynamically committed”: the two eyes'
maps will converge upon a common outcome, even if developing
independently. This dynamic fate commitment is retained even
after severe deprivation.
Development of glutamatergic synapses in the rat retina:
The postnatal expression of ionotropic glutamate receptor subunits
Authors: HACK IRIS , KOULEN PETER , PEICHL LEO , BRANDSTÄTTER JOHANN HELMUT
Published: December 2002

We examined the distribution of the AMPA glutamate receptor
subunits GluR1 to GluR4, of the kainate receptor subunits GluR6/7
and KA2, and of the glutamate receptor subunits δ1/2,
during postnatal development of the rat retina by
immunocytochemistry and light microscopy using receptor subunit
specific antisera. The various ionotropic glutamate receptor
subunits were expressed early in postnatal rat retina, and most
of the subunits, with the exception of δ1/2, were found
in both synaptic layers of rat retina. The glutamate receptor
subunits studied showed differences in their time of appearance,
their spatial distribution patterns, and in their expression
levels in the developing rat retina. Interestingly, most of
the AMPA receptor subunits were expressed earlier than the kainate
receptor subunits in the two synaptic layers of the retina,
indicating that AMPA glutamate receptors play an important role
in early postnatal glutamatergic synaptic transmission. We also
studied the ultrastructural localization of the AMPA glutamate
receptor subunits GluR1 to GluR4 by immunocytochemistry and
electron microscopy in the inner plexiform layer of the mature
rat retina. Most of the subunits were found postsynaptic to
the ribbon synapses of OFF-cone, ON-cone, and rod bipolar cells.
The results of this study suggest an involvement of ionotropic
glutamate receptors in processes of synaptic maturation and
the formation of synaptic circuitries in the developing plexiform
layers of the retina. Furthermore, AMPA and kainate receptors
play a role in synaptic processing and in the development of
both the scotopic and photopic pathways in the rat retina.
The pupillary and ciliary components of the cat Edinger-Westphal
nucleus: A transsynaptic transport investigation
Authors: ERICHSEN JONATHAN T. , MAY PAUL J.
Published: December 2002

The distribution of preganglionic motoneurons supplying the
ciliary ganglion in the cat was defined both qualitatively and
quantitatively. These cells were retrogradely labeled directly,
following injections of wheat germ agglutinin conjugated to
horseradish peroxidase (WGA-HRP) into the ciliary ganglion,
or were transsynaptically labeled following injections of WGA
into the vitreous chamber. Almost half of the cells are distributed
rostral to the oculomotor nucleus, both in and lateral to the
anteromedian nucleus. Of the remaining preganglionic motoneurons,
roughly 20% of the total are located dorsal to the oculomotor
nucleus. Strikingly few of these neurons are actually found
within the Edinger-Westphal nucleus proper. Instead, the majority
are found in the adjacent supraoculomotor area or along the
midline between the two somatic nuclei. An additional population,
roughly 30% of the total, is located ventral to the oculomotor
nucleus. This study also provides evidence for a functional
subdivision of this preganglionic population. Pupil-related
preganglionic motoneurons were transsynaptically labeled by
injecting WGA into the anterior chamber, while lens-related
preganglionic motoneurons were transsynaptically labeled by
injecting WGA into the ciliary muscle. The results suggest that
the pupil-related preganglionic motoneurons, that is, those
controlling the iris sphincter pupillae muscle, are located
rostrally, in and lateral to the anteromedian nucleus. In contrast,
lens-related preganglionic motoneurons, that is, those controlling
the ciliary muscle are particularly prevalent caudally, both
dorsal and ventral to the oculomotor nucleus. Thus, the cat
intraocular muscle preganglionic innervation is spatially organized
with respect to function, despite the dispersed nature of its
distribution.
Residual eye-movements in macaque and their effects on visual
responses of neurons
Authors: FORTE JASON , PEIRCE JONATHAN W. , KRAFT JAMES M. , KRAUSKOPF JOHN , LENNIE PETER
Published: December 2002

We recorded continuously, with high precision, the positions
of the eyes in anesthetized macaque monkeys prepared for
physiological recording. Most recordings were made after the
infusion of muscle relaxant to immobilize the eyes; in some
cases we also were able to record eye position for periods before
the eyes were immobilized. In all monkeys, the eyes moved
continuously by as much as 0.5 deg over a 10-min sampling period.
The average distance moved was proportional to the square root
of the sampling period, as would be expected from a random walk.
The movements had three distinct components: slow drifts, and
two rhythms driven by the pulse and respiration. The rhythmic
movements occurred only under paralysis: they were not discernible
in measurements made before the infusion of muscle relaxant.
The movements of the eye in the paralyzed animal can have
substantial effects on the measured physiological characteristics
of neurons. For excursions in the midrange of those we observed,
a neuron's sensitivity to a spatial frequency of 10 cycle/deg
might be underestimated by as much as a factor of three, depending
on the method by which responses were averaged. We show how
the effects of eye-movements can be mitigated by appropriate
data analysis.
Optical imaging of orientation and ocular dominance maps
in area 17 of cats with convergent strabismus
Authors: ENGELMANN RALF , CROOK JOHN M. , LÖWEL SIEGRID
Published: December 2002

Strabismus (or squint) is both a well-established model for
developmental plasticity of the brain and a frequent clinical
symptom. While the layout and topographic relationship of
functional domains in area 17 of divergently squinting cats
has been analyzed extensively in recent years (e.g. Löwel
et al., 1998), functional maps in convergently squinting animals
have so far not been visualized with comparable detail. We have
therefore investigated the functional organization of area 17
in adult cats with a surgically induced convergent squint angle.
In these animals, visual acuity was determined by both behavioral
tests and recordings of visual evoked potentials, and animals
with comparable acuities in both eyes were selected for further
experiments. The functional layout of area 17 was visualized
using optical imaging of intrinsic signals. Monocular
iso-orientation domains had a patchy appearance and their layout
was different for left and right eye stimulation, so that
segregated ocular dominance domains could be visualized.
Iso-orientation domains exhibited a pinwheel-like organization,
as previously described for normal and divergently squinting
cats. Mean pinwheel density was the same in the experimental
and control animals (3.4 pinwheel centers per mm2
cortical surface), but significantly (P < 0.00001)
higher than that reported previously for normal and divergently
squinting cats (2.7/mm2). A comparison of orientation
with ocular dominance maps revealed that iso-orientation domains
were continuous across the borders of ocular dominance domains
and tended to intersect these borders at steep angles. However,
in contrast to previous reports in normally raised cats,
orientation pinwheel centers showed no consistent topographical
relationship to the peaks of ocular dominance domains. Taken
together, these observations indicate an overall similarity
between the functional layout of orientation and ocular dominance
maps in area 17 of convergently and divergently squinting cats.
The higher pinwheel densities compared with previous reports
suggest that animals from different gene pools might generally
differ in this parameter and therefore also in the space constants
of their cortical orientation maps.
Synaptic inputs of class III and class V interneurons in
the cat pulvinar nucleus: Differential integration of RS and
RL inputs
Authors: CARDEN Wm. BRECKINRIDGE , BICKFORD MARTHA E.
Published: December 2002

We previously reported that two types of visual thalamic
interneurons (class III and class V) could be distinguished
by the presence or absence of the enzyme brain nitric oxide
synthase (bNOS; Bickford et al., 1999). In the present study,
we found that further immunocytochemical characterization can
be used to isolate class V and class III neurons: class V neurons
express GABA and bNOS but not the calcium binding protein
calbindin, whereas class III neurons express GABA and calbindin,
but not bNOS. By pairing staining for bNOS or calbindin with
staining for GABA, we were able to distinguish class III and
class V neurons, thereby allowing us to characterize the synaptic
inputs to these two interneuron populations within the cat pulvinar
nucleus. We found class III and class V interneurons participate
in distinctly different circuitries. Class III cells receive
the majority of their input from large terminals with round
vesicles (RL profiles, that presumably originate from cortical
layer V) while class V cells receive all of their input from
small terminals with round vesicles (RS profiles, that presumably
originate from cortical layer VI). These two types of interneurons
also target different regions of the dendritic arbors of
thalamocortical cells; class III cells contact large caliber
(presumably proximal) thalamocortical dendrites within glomeruli,
while class V cells contact the small caliber (presumably distal)
thalamocortical cell dendrites within the extraglomerular neuropil.
Thus, a dual inhibitory system exists within the visual thalamus
that integrates different types of corticothalamic input and
targets distinct regions of thalamocortical cell dendritic arbors.
Mapping photoreceptor and postreceptoral labelling patterns
using a channel permeable probe (agmatine) during development
in the normal and RCS rat retina
Authors: KALLONIATIS MICHAEL , TOMISICH GUIDO , WELLARD JOHN W. , FOSTER LISA E.
Published: December 2002

The aim of this study was to determine whether agmatine, a
channel permeable probe, can identify photoreceptor dysfunction
in the Royal College of Surgeons (RCS) retina at an earlier
stage to that shown by apoptosis or anatomical markers, and
also characterize the neurochemical development of the inner
retina in the normal and degenerating rat. We used isolated
retinas at different ages incubated in physiological media
containing agmatine. Subsequently, postembedding
immunocytochemistry was used to determine the number of labelled
photoreceptors and the labelling pattern within postreceptoral
neurons. Agmatine labelling patterns revealed a sequential
development of retinal neurons beginning at postnatal day
(PND)11/12 with most horizontal cells, a few ganglion and amacrine
cells, showing a strong signal. The neurochemical development
progressed rapidly, and reflects to a large part the known
distribution of glutamate receptors, with inner nuclear labelling
being evident by PND14, continuing with the same pattern of
labelling in adulthood for the control retina. The RCS retina
showed markedly reduced agmatine labelling in the inner retina
at PND20. A rapid increase in photoreceptor AGB labelling was
evident during the degeneration phase. Multiple samples at PND14
and PND16 confirmed a significant increase of labelled
photoreceptors in the RCS retina.
Spatial-chromatic interactions in C-type horizontal cells
of the turtle (Mauremys caspica) retina
Authors: TWIG G. , LEVY H. , PERLMAN I.
Published: December 2002

Horizontal cells are second-order retinal neurons that play
a key role in spatial information processing. In some cold-blooded
vertebrates such as turtles, a subtype of these cells, the
chromaticity horizontal cells exhibit color-opponent responses
and therefore are considered to be important also for color
information processing. To reveal spatial and color interactions,
the receptive-field properties of Red/Green and Yellow/Blue
chromaticity horizontal cells in the retina of the turtle
Mauremys caspica were studied by intracellular recordings
from the everted eyecup preparation. We found that the polarity
of the photoresponses depended not only upon the wavelength
and intensity of the stimulus, but also upon its spatial
configuration. Thus, a hyperpolarizing photoresponse that was
elicited by full-field stimulation with bright light of wavelength
close to the “neutral” one was reversed in polarity
to a pure depolarizing one when a small spot or a thin annular
pattern were used for stimulation. This finding could not be
explained either by different balances between depolarizing
and hyperpolarizing inputs to different cells or by stray light
that effectively reduced the light intensity in the center of
the small spot. Rather, it was found that the depolarizing and
hyperpolarizing components were characterized by different
receptive-field size and that these differences could account
for the dependency of response polarity upon the spatial pattern
of the stimulus. These findings indicate that color information
processing in turtle C-type horizontal cells is a complex process
that depends upon the wavelength and intensity of the light
stimulus as well as upon its spatial properties.
Are primate lateral geniculate nucleus (LGN) cells really
sensitive to orientation or direction?
Authors: XU XIANGMIN , ICHIDA JENNIFER , SHOSTAK YURI , BONDS A.B. , CASAGRANDE VIVIEN A.
Published: December 2002

There is considerable controversy over the existence of
orientation and direction sensitivity in lateral geniculate
nucleus (LGN) neurons. Claims for the existence of these properties
often were based upon data from cells tested well beyond their
peak spatial frequencies. The goals of the present study were
to examine the degree of orientation and direction sensitivity
of LGN cells when tested at their peak spatial and temporal
frequencies and to compare the tuning properties of these
subcortical neurons with those of visual cortex. For this
investigation, we used conventional extracellular recording
to study orientation and direction sensitivities of owl monkey
LGN cells by stimulating cells with drifting sinusoidal gratings
at peak temporal frequencies, peak or higher spatial frequencies,
and moderate contrast. A total of 110 LGN cells (32 koniocellular
cells, 34 magnocellular cells, and 44 parvocellular cells) with
eccentricities ranging from 2.6 deg to 27.5 deg were examined.
Using the peak spatial and temporal frequencies for each cell,
41.8% of the LGN cells were found to be sensitive to orientation
and 19.1% were direction sensitive. The degree of bias for
orientation and direction did not vary with eccentricity or
with cell class. Orientation sensitivity did, however, increase,
and in some cases orientation preferences changed, at higher
spatial frequencies. Increasing spatial frequency had no consistent
effect on direction sensitivity. Compared to cortical cell
orientation tuning, the prevalence and strength of LGN cell
orientation and direction sensitivity are weak. Nevertheless,
the high percentage of LGN cells sensitive to orientation even
at peak spatial and temporal frequencies reinforces the view
that subcortical biases could, in combination with
activity-dependent cortical mechanisms and/or cortical inhibitory
mechanisms, account for the much narrower orientation and direction
tuning seen in visual cortex.
Differential distributions of red–green and
blue–yellow cone opponency across the visual field
Authors: MULLEN KATHY T. , KINGDOM FREDERICK A.A.
Published: December 2002

The color vision of Old World primates and humans uses two
cone-opponent systems; one differences the outputs of L and M
cones forming a red–green (RG) system, and the other
differences S cones with a combination of L and M cones forming
a blue–yellow (BY) system. In this paper, we show that
in human vision these two systems have a differential distribution
across the visual field. Cone contrast sensitivities for sine-wave
grating stimuli (smoothly enveloped in space and time) were
measured for the two color systems (RG & BY) and the achromatic
(Ach) system at a range of eccentricities in the nasal field
(0–25 deg). We spatially scaled our stimuli independently
for each system (RG, BY, & Ach) in order to activate that
system optimally at each eccentricity. This controlled for any
differential variations in spatial scale with eccentricity and
provided a comparison between the three systems under equivalent
conditions. We find that while red–green cone opponency
has a steep decline away from the fovea, the loss in
blue–yellow cone opponency is more gradual, showing a
similar loss to that found for achromatic vision. Thus only
red–green opponency, and not blue–yellow opponency,
can be considered a foveal specialization of primate vision
with an overrepresentation at the fovea. In addition, statistical
calculations of the level of chance cone opponency in the two
systems indicate that selective S cone connections to
postreceptoral neurons are essential to maintain peripheral
blue–yellow sensitivity in human vision. In the
red–green system, an assumption of cone selectivity is
not required to account for losses in peripheral sensitivity.
Overall, these results provide behavioral evidence for functionally
distinct neuro-architectural origins of the two color systems
in human vision, supporting recent physiological results in
primates.
Coupling pattern of S1 and S2 amacrine cells in the rabbit retina
Authors: LI WEI , ZHANG JIAN , MASSEY STEPHEN C.
Published: December 2002

Previous studies have shown that indoleamine-accumulating cells
(IACs) in the rabbit retina consist of two main cell types:
S1 and S2 amacrine cells (Vaney, 1986; Sandell & Masland,
1986). Both cell types are wide-field GABA amacrine cells that
make reciprocal synaptic contacts with rod bipolar cell terminals
(Ehinger & Holmgren, 1979; Strettoi et al., 1990). We have
examined the coupling pattern of S1 and S2 amacrine cells after
the intracellular injection of Neurobiotin. Our results may
be summarized as follows: (1) S1 amacrine cells were extensively
coupled and their dendrites formed a network similar to but
less dense than the matrix stained with an antibody to serotonin.
(2) Morphological observations and cluster analysis, based on
a scattergram, showed that the vast majority of coupled cells
were S1 amacrine cells, accounting for approximately half of
the total IACs. The rest of the uncoupled IACs were S2 amacrine
cells. (3) Sometimes, two adjacent varicosities, one from an
injected S1 and one from a coupled S1, contacted a single rod
bipolar terminal. (4) S2 amacrine cells were also coupled but
much less than the S1s. (5) Rarely, crossover coupling between
S1 and S2 amacrine cells was observed. These results suggest
that the extensive coupling between S1 amacrine cells, combined
with a larger dendritic field, may contribute a wide-field
component to the inhibitory surround of the rod pathway. By
comparison, the smaller, weakly coupled S2 amacrine cells may
provide a local component.
Contextual influences on the directional responses of tectal
cells in pigeons
Authors: SUN HONG-JIN , ZHAO JIAN , SOUTHALL TRACY L. , XU BIN
Published: December 2002

Contrary to the traditional view that receptive fields are
limited in spatial extent, recent studies have indicated that
the response of neurons to a local stimulus within the receptive
field can be modulated by stimulation of the surrounding region.
Here we quantified the nature of these contextual effects on
visual motion responses of neurons in the pigeon's optic
tectum using standard extracellular recording techniques. All
of the cells tested responded well to a test spot moving across
their receptive fields. When a background pattern was moved
in the same or in a similar direction as that of the test spot,
the responses of most deep tectal neurons to the test spot were
maximally inhibited. Movement of the background in the opposite
or near opposite direction produced minimal inhibition or even
facilitation. For some deep tectal neurons, this directionally
selective modulation by the moving background was maintained
when the background motion was paired with different movement
directions of the test spot (including both the preferred and
least preferred directions). Thus, this selectivity for opposing
motion was independent of the absolute direction of either the
test spot or the background, a finding which is consistent with
the results reported by Frost and Nakayama (1983), although
they did not include all test spot directions. For some other
neurons, identified here for the first time, the background
movement selectively modulated the response only when the test
spot moved in the neuron's preferred directions. These
neurons lost selectivity for opposing motion when the test spot
moved in nonpreferred directions. The significance of these
contextual effects on the motion response of tectal neurons
may be related to how the brain distinguishes self-induced motion
from object motion and segregates figure from ground.
A structural basis for omnidirectional connections between
starburst amacrine cells and directionally selective ganglion
cells in rabbit retina, with associated bipolar cells
Authors: FAMIGLIETTI E.V.
Published: December 2002

Directionally selective (DS) ganglion cells of rabbit retina
are of two principal types. ON DS ganglion cells prefer low
velocity in one of three directions of movement and project
axons to the accessory optic system (AOS), whereas ON–OFF
DS ganglion cells prefer higher velocity in one of four directions
and project to tectum and thalamus. Each has a distinct,
recognizable dendritic morphology, based upon the correlation
of form, physiology, and central projections. In previous Golgi
studies, ON and ON–OFF DS cells were found to be partly
co-stratified, and ON–OFF DS cells were found to co-stratify
with starburst amacrine (SA) cells, the cholinergic amacrine
cells of the retina, which also contain elevated levels of GABA.
SA cells are radially symmetrical, have synaptic boutons in
a distal annular zone of its dendritic tree, are presynaptic
primarily to ganglion cell dendrites, co-stratify with ON–OFF
DS ganglion cells, and contain the neurotransmitters shown
pharmacologically to be involved in DS responses. For these
reasons, SA cells are thought to play a role in the DS mechanism.
Several models of this mechanism have utilized SA cell dendritic
geometry in a centrifugal, radial format to impose directional
inputs on DS ganglion cells.