bluuebunny/crossref_metadata_2025 huggingface dataset:
The distribution of calcium-binding proteins in the lateral
geniculate nucleus and visual cortex of a New World monkey,
the marmoset, Callithrix jacchus
Authors: GOODCHILD ANN K. , MARTIN PAUL R.
Published: July 2002

Antibodies directed against the calcium-binding
proteins, parvalbumin and calbindin, can be used to label
distinct neuronal subgroups in the primate visual pathway.
We analyzed parvalbumin immunoreactivity (P-IR) and calbindin
immunoreactivity (C-IR) in the lateral geniculate nucleus
(LGN) and visual cortex of the marmoset, Callithrix
jacchus. We compared marmosets which were identified
as having dichromatic or trichromatic color vision. Within
the LGN, the density of P-IR neurones is highest in the
parvocellular and magnocellular laminae, but C-IR neurones
are found mainly in the koniocellular division of the LGN,
that is, the interlaminar zones and S laminae. Not all
interlaminar zone cells are C-IR. In the visual cortex,
P-IR neurones are present in all laminae except lamina
1, in areas V1 and V2. Neurones which are strongly C-IR
are mainly located in laminae 2 and 3 in V1 and V2. Lightly
C-IR neurones are concentrated in lamina 4, and are more
numerous in V1 than in V2. Quantitative analysis showed
no differences in the density or distribution of IR neurones
in either LGN or visual cortex when dichromat and trichromat
animals were compared. We conclude that this functional
difference is not associated with differences in the neurochemistry
of calcium-binding proteins in the primary visual pathways.
The topography of rod and cone photoreceptors in the retina
of the ground squirrel
Authors: KRYGER Z. , GALLI-RESTA L. , JACOBS G.H. , REESE B.E.
Published: July 2002

The distributions of rod and cone photoreceptors
have been determined in the retina of the California ground
squirrel, Spermophilus beecheyi. Retinas were
fixed by perfusion and the rods and cones were detected
with indirect immunofluorescence using opsin antibodies.
Local densities were determined at 2-mm intervals across
the entire retina, from which total numbers of each receptor
type were estimated and isodensity distributions were constructed.
The ground squirrel retina contains 7.5 million cones and
1.27 million rods. The peak density for the cones (49,550/mm2)
is found in a horizontal strip of central retina 2 mm ventral
to the elongated optic nerve head, falling gradually to
half this value in the dorsal and ventral retinal periphery.
Of the cones, there are 14 M cones for every S cone. S
cone density is relatively flat across most of the retina,
reaching a peak (4500/mm2) at the temporal end
of the visual streak. There is one exception to this, however:
S cone density climbs dramatically at the extreme dorso-nasal
retinal margin (20,000/mm2), where the local
ratio of S to M cones equals 1. Rod density is lowest in
the visual streak, where the rods comprise less than 5%
of the local photoreceptor population, increasing conspicuously
in the ventral retina, where the rods achieve 30% of the
local photoreceptor population (13,000/mm2).
The functional importance of the change in S to M cone
ratio at the dorsal circumference of the retina is compromised
by the extremely limited portion of the visual field subserved
by this retinal region. The significance for vision, if
any, remains to be determined. By contrast, the change
in rod/cone ratio between the dorsal and ventral halves
of the retina indicates a conspicuous asymmetry in the
ground squirrel's visual system, suggesting a specialization
for maximizing visual sensitivity under dim levels of illumination
in the superior visual field.
Rhodopsin maturation antagonized by dominant rhodopsin mutants
Authors: KURADA PHANI , TONINI TIMOTHY D. , SERIKAKU MICHELLE A. , PICCINI JONATHAN P. , O'TOUSA JOSEPH E.
Published: July 2002

ninaED1, a dominant allele
of the major Drosophila rhodopsin gene, expresses
a rhodopsin that is predominantly recovered in a 80-kD
complex that likely represents rhodopsin dimers. By driving
either ninaED1 or ninaE+
expression from a heat-shock promoter, we show that the
80-kD rhodopsin complex forms immediately after gene activation.
In wild type, but not ninaED1, rhodopsin
monomeric forms are detected at later times. The generation
of monomeric forms of wild-type rhodopsin is suppressed
in vitamin A-deprived flies or in flies heterozygous for
the dominant rhodopsin mutation. We also show that ninaED1
expression does not affect the maturation of another Drosophila
visual pigment, Rh3. These results are consistent with
the view that the ninaED1 rhodopsin
antagonizes an early posttranslation process that is specific
for maturation of the ninaE-encoded rhodopsin.
Increased absolute light sensitivity in Himalayan mice with
cold-induced ocular pigmentation
Authors: BALKEMA GRANT W. , MacDONALD SHANNON
Published: July 2002

Controversy over the relationship between ocular
pigmentation and absolute dark-adapted light sensitivity
has persisted for over two decades. Previous electrophysiological
experiments in hypopigmented mammals (mice, rats, rabbits)
show increased thresholds in the dark-adapted state proportional
to the deficit in ocular melanin. Animals with the least
amount of ocular melanin have the most elevated thresholds.
Dark-adapted thresholds in hypopigmented mice show similar
threshold elevations in behavioral tests. The present study
extends these findings to show that a specific increase
in ocular pigmentation results in the converse effect,
lowered absolute dark-adapted thresholds. The increase
in ocular melanin was accomplished by keeping Himalayan
mice in the cold (4°C) for 6 weeks. Himalayan mice
(C57BL/6J cH/cH) were compared to
black mice (C57BL/6J +/+) and albino mice (C57BL/6J c2J/c2J)
after 6 weeks at either 4°C or 20°C in 12-h cycling
light (<1 cd/m2). The Himalayan mice that
were kept in the cold exhibited a 44% increase in ocular
melanin compared to Himalayan mice kept at room temperature.
Cold rearing did not effect ocular melanin or visual thresholds
in control animals (black mice = 10−5.9
cd/m2 and albino mice = 10−4.4
cd/m2). In contrast, the Himalayan mice maintained
at 4°C had thresholds of 10−5.7 cd/m2
compared to 10−5.1 cd/m2 for
Himalayan mice kept at 20°C. This represents compelling
evidence of a direct relationship between ocular melanin
concentration and absolute dark-adapted light sensitivity.
Spectral sensitivity of the goldfish Torus longitudinalis
Authors: GIBBS M.A. , NORTHMORE D.P.M.
Published: July 2002

We measured the photopic spectral sensitivity of
multiunit activity in the torus longitudinalis and optic
tectum of goldfish. Since negative contrast stimuli are
most effective for exciting torus longitudinalis, spiking
activity was evoked by the shadow of a disc moving through
a monochromatic light beam projected upon a screen. The
amount of activity evoked in torus longitudinalis generally
increased with the monochromatic stimulus radiance at the
same rate for all wavelengths, indicating a univariant
response. Spiking activity in tectum, however, increased
at different rates across the spectrum, indicating color-dependent
responses. The action spectra for torus longitudinalis
were all similar and relatively flat as expected of a homogeneous,
broad-band luminance processing system, and about 1 log
unit more sensitive than the tectal action spectra. The
latter generally displayed sharp peaks and dips in sensitivity
indicative of opponent processing.
Localization of nitric oxide synthase, NADPH diaphorase
and soluble guanylyl cyclase in adult rabbit retina
Authors: HABERECHT MICHAEL F. , SCHMIDT HARALD H.H.W. , MILLS STEPHEN L. , MASSEY STEVEN C. , NAKANE MASAKI , REDBURN-JOHNSON DIANNA A.
Published: July 2002

Nitric oxide (NO) acts as a neuronal messenger
which activates soluble guanylyl cyclase (SGC) in neighboring
cells and produces a wide range of physiological effects
in the central nervous system (CNS). Using immunocytochemical
and histochemical stains, we have characterized the NO/SGC
system in the rabbit retina and to a lesser extent, in
monkey retina. Based on staining patterns observed with
an antibody to nitric oxide synthase (NOS) type I and a
histochemical marker for NADPH diaphorase, a metabolic
intermediate required for NOS activity, three major classes
of neurons appear to generate NO in the rabbit retina.
These include two subclasses of sparsely distributed wide
field amacrine cells, rod and cone photoreceptors, and
a subpopulation of ganglion cells. Equivalent cell populations
were labled in monkey retina. An antibody to SGC (tested
only in rabbit retina), labeled large arrays of cone photoreceptors
in the outer nuclear layer, both amacrine and bipolar cells
in the inner nuclear layer (INL), as well as populations
of neurons in the ganglion cell layer. These data suggest
that the ability to generate NO is restricted to relatively
few neurons in the inner retina and to photoreceptor cells
in the outer retina; while presumptive target cells, containing
pools of SGC, are widespread and form contiguous fields
across the inner and outer nuclear layers (ONL) as well
as the ganglion cell layer.
Electroretinographic evaluation of spectral sensitivity
in yellow and silver eels (Anguilla anguilla)
Authors: ANDJUS R.K. , DAMJANOVIĆ I. , GAČIĆ Z. , KONJEVIĆ DJ. , ANDJUS P.R.
Published: July 2002

Although differences in visual pigments between
developmental stages of the European eel are well known,
the expected differences in spectral sensitivity have not
been demonstrated at the electrophysiological level. In
fact, one past electroretinographic study led to the conclusion
that in eels there is no change in scotopic sensitivity,
with increasing sexual maturity. In the present experiments,
electroretinograms (ERGs) were recorded from in situ
eyecups of immobilized eels Anguilla anguilla
(L.) caught in coastal running waters. It was shown that
the ERG b-wave is as good an indicator of spectral
sensitivity as the unmasked late receptor potential (LRP)
which directly reflects the responsiveness of photoreceptors.
Complete spectral-sensitivity curves, based on b-wave
thresholds and on thresholds of LRP subsequently isolated
by means of sodium iodate, have been obtained in the same
eel. Using fitted amplitude-log intensity functions for
threshold calculation, and two models for computer-assisted
fitting of spectral-sensitivity curves, significant differences
in λmax were found between yellow and silver
developmental stages of the eel, identified by ocular index
measurements.
Monocular enucleation prevents retinal ganglion-cell loss
following neonatal visual cortex damage in cats
Authors: ILLIG KURT R. , KING VON R. , SPEAR PETER D.
Published: July 2002

Damage to primary visual cortex (VC) in young cats
leads to severe retrograde degeneration of the dorsal lateral
geniculate nucleus (dLGN) and selective transneuronal retrograde
degeneration of a class of retinal ganglion cells (RGCs)
that have a medium-size soma. Previous studies have shown
that “programmed” RGC death associated with
normal development in one eye can be attenuated by removal
of the other eye, suggesting that binocular interactions
can influence developmental RGC death. The present study
investigated whether removal of one eye also attenuates
the ganglion cell loss that accompanies an early VC lesion.
Five one-week-old cats received a unilateral VC lesion
(areas 17, 18, and 19), and three of these cats also underwent
monocular enucleation at the same time. Two normal control
animals also were examined. RGC measurements were made
from flat-mounted retinae when the animals were 5 weeks
old. Sampling was restricted to a retinal area corresponding
to the retinotopic representation included in the VC lesion.
Results indicate that there is a marked loss of medium-size
RGCs in the hemiretinae projecting to the damaged hemisphere
in cats that received a VC lesion alone. However, there
is no such loss in VC-lesion animals that also have a monocular
enucleation. These results indicate that the transneuronal
RGC loss that occurs after an early visual cortex lesion
can be influenced by binocular interactions.
Complementary roles of two excitatory pathways in retinal
directional selectivity
Authors: GRZYWACZ NORBERTO M. , MERWINE DAVID K. , AMTHOR FRANKLIN R.
Published: July 2002

The two major excitatory synapses onto ON–OFF
directionally selective (DS) ganglion cells of the rabbit
retina appear to be nicotinic cholinergic and NMDA glutamatergic.
Blockade of either of these synapses with antagonists does
not eliminate directional selectivity. This suggests that
these synapses may have complementary roles in the computation
of the direction of motion. To test this hypothesis, quantitative
features of the DS cell excitatory pathways were determined
by collecting responses, under nicotinic and/or NMDA blockade,
to a sweeping bar, hyperacute apparent motions, or a drifting
sinusoidal grating. Sweeping bar responses were reduced,
but directional selectivity not eliminated, by blockade
of either excitatory path, as previously shown (Cohen &
Miller, 1995; Kittila & Massey, 1997). However, residual
responses under combined blockades were not statistically
significantly DS. NMDA blockade reduced responses more
than nicotinic blockade for each protocol, and shifted
hyperacute motion thresholds to higher values. This supported
the notion that glutamate provides the main excitatory
drive to DS cells, that is, the one responsible for contrast
sensitivity. In turn, nicotinic, but not NMDA blockade
eliminated directional selectivity to a drifting low spatial-frequency
sinusoidal grating in these cells. This suggested that
acetylcholine (ACh) is the main excitatory input with regards
to directional selectivity for some textured stimuli, that
is, those with multiple peaks in their spatial luminance
profile. Moreover, nicotinic blockade raised the low temporal-frequency
cutoff of the grating responses, consistent with the proposal
that preferred-direction facilitation, which is temporally
sustained, is dependent on the cholinergic input. These
different properties of the NMDA and nicotinic pathways
are consistent with a recently proposed two-asymmetric-pathways
model of directional selectivity.
Functional properties of retinal ganglion cells during optic
nerve regeneration in the goldfish
Authors: OH D.-J. , NORTHMORE D.P.M.
Published: July 2002

After being severed, optic axons in goldfish regenerate
and eventually restore the retinotectal map; refinement
of the map depends upon impulse activity generated by the
ganglion cells. Because little is known about the changes
in activity and receptive-field properties of ganglion
cells during regeneration, we made extracellular recordings
from them in the intact eye up to 95 days after sectioning
their axons in the optic tract. Their receptive fields
were classified as OFF-, ON–OFF-, or ON-centers,
and their axonal conduction velocities measured by antidromic
activation. The rate of encountering single units dropped
drastically at 4–8 days postsection when only a few
OFF-center units could be recorded, recovering to normal
between 42 and 63 days. Receptive-field centers were normal
in size, except for the few OFF-centers at 4–8 days
which were abnormally large. Maintained discharge rates
of all types were depressed up to 42 days, but ON–OFF-center
units were more spontaneously active than normal around
42 days. Light-evoked responses in OFF-center units were
subnormal at 4–8 days, becoming supernormal at 16
days and normal thereafter. ON–OFF- and ON-center
units started to regain responsiveness at 16 days, and
became supernormal at 42 days, before returning to normal.
Conduction velocities of all fiber groups dropped to a
minimum at 8 days, the fastest being affected most. There
was a gradual recovery to normal conduction velocity by
63 days. The conduction latencies of OFF- and ON–OFF-center
units recovered to normal by 42 days, and ON-center units
by 63 days. Recovery of ganglion cell responsiveness correlates
with functional recovery in the retinotectal system: OFF-center
units recover light-evoked responses at about the time
OFF activity first reappears in the tectum. ON- and ON–OFF-center
units recover later, exhibiting supernormal spiking activity
around the time that ON responses reappear in the tectum.
Identification and distribution of photoreceptor subtypes
in the neotenic tiger salamander retina
Authors: SHERRY DAVID M. , BUI DAI D. , DEGRIP WILLEM J.
Published: July 2002

The neotenic tiger salamander retina is a major
model system for the study of retinal physiology and circuitry,
yet there are unresolved issues regarding the organization
of the photoreceptors and the photoreceptor mosaic. The
rod and cone subtypes in the salamander retina were identified
using a combination of morphological and immunocytochemical
markers for specific rod and cone opsin epitopes. Because
the visual pigment mechanisms present in the tiger salamander
retina are well characterized and the antibodies employed
in these studies are specific for particular rod and cone
opsin epitopes, we also were able to identify the spectral
class of the various rod and cone subtypes. Two classes
of rods corresponding to the “red” and “green”
rods previously reported in amphibian retinas were identified.
In serial semithin section analyses, rods and cones comprised
62.4 ± 1.4% and 37.6 ± 1.4% of all photoreceptors,
respectively. One rod type comprising 98.0 ± 0.7%
of all rods showed the immunological and morphological
characteristics of “red” rods, which are maximally
sensitive to middle wavelengths. The second rod subtype
comprised 2.0 ± 0.7% of all rods and possessed the
immunological and morphological characteristics of “green”
rods, which are maximally sensitive to short wavelengths.
By morphology four cone types were identified, showing
three distinct immunological signatures. Most cones (84.8
± 1.5% of all cones), including most large single
cones, the accessory and principal members of the double
cone, and some small single cones, showed immunolabeling
by antisera that recognize long wavelength-sensitive cone
opsins. A subpopulation of small single cones (8.4 ±
1.7% of all cones) showed immunolabeling for short wavelength-sensitive
cone opsin. A separate subpopulation of single cones which
included both large and small types (6.8 ± 1.4%
of all cones) was identified as the UV-Cone population
and showed immunolabeling by antibodies that recognize
rod opsin epitopes. Analysis of flatmounted retinas yielded
similar results. All photoreceptor types appeared to be
distributed in all retinal regions. There was no obvious
crystalline organization of the various photoreceptor subtypes
in the photoreceptor mosaic.
The d-wave of the rod electroretinogram of rat
originates in the cone pathway
Authors: NAARENDORP FRANK , WILLIAMS GEORGE E.
Published: July 2002

We studied the off-response of the rat ERG evoked
with long duration, mesopic stimuli during light and dark
adaptation, and after intravitreal injection of aspartate
and (±)-cis-piperidine-2,3-dicarboxilic
acid (PDA). At stimulus offset, the dark-adapted ERG always
showed a rapid negative deflection followed by a positive
deflection after which the potential returned to baseline.
When the stimulus was turned off in the presence of a background
of scotopic intensity, the positive deflection consisted
of two components. One component was relatively small,
fast, and insensitive to rod light adaptation. It resembled
the d-wave of the rod ERG. The other component
was slow and its amplitude grew with rod light adaptation.
In the presence of aspartate, the fast-positive component
was absent from the ERG while the remaining positive-going
decay of the receptor potential had a time course similar
to that of the slow-positive component in the untreated
eye. Scotopically matched red and blue stimuli of mesopic
intensity elicited equal ERG responses from the dark-adapted
eye, including the two positive components in the off-response.
These stimuli were also used to assess changes in the ERG
off-response during recovery from a strong bleach. Even
though the cone contribution to the rat ERG is very small,
the presence of a small positive-going component in the
off-response following an intense bleach suggested that
this response originated from the cone pathway. PDA which
suppresses the light response of hyperpolarizing bipolar
cells and horizontal cells selectively eliminated the fast-positive
component from the ERG. The findings of this study are
inconsistent with the idea that the d-wave reflects
the decay of the rod receptor potential. They support the
possibility that signals from rods cross rod–cone
gap junctions at mesopic light intensities, and drive second-order
neurons in the cone pathway.
Distribution of GABAC-like responses among acutely
dissociated rat retinal neurons
Authors: NELSON RALPH , SCHAFFNER ANNE E. , LI YONG-XIN , WALTON MARC K.
Published: July 2002

GABAergic responses of acutely dissociated rat
retinal neurons, including both bipolar cells (BCs) and
other, morphologically round cells (RCs), were assayed
with the fluorescent (FL), voltage-sensitive probe oxonol
DiBaC4(5). Using intensified video microscopy
and simultaneous recording, GABA responses were identified
in one-third of cells in a typical microscope field; of
these 85% hyperpolarized (0.05–0.3 log unit FL decreases)
while the remainder depolarized (0.05–0.2 log unit
FL increases). GABA-sensitive cells were also TACA-sensitive
(trans-4-Aminocrotonic acid), and these ligands
appeared interchangeable in ability to evoke responses.
In RCs, an asymmetric co-responsive pattern was observed
between GABA- and muscimol-evoked events. Muscimol-sensitive
RCs responded well to GABA, but not all GABA-sensitive
RCs responded to muscimol. In GABA-sensitive BCs, muscimol
responses were typically weak or absent. Few BCs or RCs
responded to CACA (cis-4-Aminocrotonic acid).
Bicuculline-resistant GABA responses occurred in ∼80%
of GABA-responsive RCs and BCs. Both bicuculline-sensitive
(GABAA-like) and bicuculline-insensitive (GABAC-like)
responses were resistant to picrotoxin. Although a small
minority of GABA-sensitive cells hyperpolarized in response
to R(+)baclofen, bicuculline-insensitive responses were
not antagonized by 2-hydroxysaclofen, and were abolished
in low [Cl−]o. Results
suggested (1) that bicuculline-insensitive, Cl−-dependent,
GABAC-like responses were broadly distributed
and predominant among dissociated rat retinal neurons;
(2) that muscimol was a particularly weak agonist for rat
retinal BCs; and (3) that oxonol was a sensitive probe
for retinal GABA responses.
5-HT2a receptors in the rabbit retina: Potential
presynaptic modulators
Authors: POOTANAKIT KUSOL , PRIOR KATHERINE J. , HUNTER DALE D. , BRUNKEN WILLIAM J.
Published: July 2002

Three 5-HT receptors have been implicated in retinal
processing but positive identification of the receptors
and the localization of receptor subtypes in the retina
have not been achieved. In this study, molecular techniques
were used to identify one class of 5-HT receptor—5-HT2a—in
the retina, and immunohistochemical techniques were used
to localize the receptor in the retinal network. Reverse
transcription polymerase chain reaction (RT-PCR) techniques
were used to identify a segment of the rabbit 5-HT2a
gene; a 422 base fragment was identified, cloned, and sequenced.
The fragment shows a high degree (ca. 90%) of
nucleotide sequence identity with the 5-HT2a
receptor gene from other mammals. 5-HT2a immunoreactivity
was seen in both the inner and outer plexiform (synaptic)
layers of the retina. Using cell-type-specific markers,
the 5-HT2a immunoreactivity was shown to be
on the terminals of photoreceptor and rod bipolar cells.
This association of 5-HT2a receptors with these
two synapses suggests that serotonin may be a modulator
of synaptic function in the retina.
Origin of tectal cholinergic projections in amphibians:
A combined study of choline acetyltransferase immunohistochemistry
and retrograde transport of dextran amines
Authors: MARÍN OSCAR , GONZÁLEZ AGUSTÍN
Published: July 2002

Immunohistochemistry for choline acetyltransferase
(ChAT) revealed an extensive network of cholinergic fibers
in the tectum of amphibians. The distribution of ChAT immunoreactive
fibers was not restricted to superficial retinocipient
layers, but also included deep tectal layers. The aim of
the present study was to investigate the origin of the
cholinergic inputs to the tectum of amphibians. For that
purpose, application of retrograde tracers in the tectum
of the anuran Rana perezi and the urodele Pleurodeles
waltl was combined with ChAT immunohistochemistry.
Double-labeled cells were found primarily in the nucleus
isthmi of both species. The cholinergic isthmotectal projection
is bilateral and topographically arranged and all retrogradely
labeled cells found in this nucleus were ChAT immunoreactive.
Remarkably, abundant cholinergic cells in two tegmental
nuclei, the pedunculopontine tegmental nucleus (anurans)
and the laterodorsal tegmental nucleus (anurans and urodeles),
were demonstrated to provide additional cholinergic innervation
to the tectum. We compare the present results with previously
reported studies in amphibians and other vertebrates, and
discuss the possible functional significance of the cholinergic
innervation of the amphibian tectum.
Distribution of photoreceptor types in the retina of a marsupial,
the tammar wallaby (Macropus eugenii)
Authors: HEMMI JAN M. , GRÜNERT ULRIKE
Published: July 2002

Mammalian retinae generally contain low numbers
of short-wavelength-sensitive cones (S-cones) and higher
numbers of middle- to long-wavelength-sensitive cones (M-cones).
Some recent studies found topographic differences between
the different photoreceptor types and in some instances
between photoreceptors and ganglion cells. To investigate
this question further, we constructed topographical maps
of the different photoreceptors found in an Australian
marsupial, the tammar wallaby. We used two polyclonal antibodies
that have been shown to label S-cones (JH455) or M-cones
(JH492) in a range of mammals. In the tammar wallaby, the
antisera clearly distinguish two cone types. JH455 recognizes
a small subset of cones (S-cones) with a density of less
than 500 cells/mm2 in the ventral retina. Their
density increases towards the dorsal retina to about 1600–2000
cells/mm2. JH492 recognizes all remaining cones
(M-cones), but also faintly labels most cone cells recognized
by JH455. The distribution of M-cones, unlike that of the
S-cones, shows a clear horizontal streak of high cell density
through the central retina, just like the ganglion cells.
Unlike the ganglion cells, however, the M-cones do not
peak in the temporal retina but show a very broad peak
(12,000–18,000 cells/mm2) in the central
or even slightly nasal retina. Based on our findings, the
retina of the tammar can be divided into three distinct
regions: firstly, the dorsal retina, which has a low ganglion
and low cone cell density but a high percentage of S-cones
(30%), is thought to provide good spectral sensitivity;
secondly, the central horizontal band of retina, which
has a high ganglion and high cone cell density and therefore
provides good spatial resolution; and thirdly, the ventral
retina, which has a low ganglion cell but high cone cell
density with few S-cones (5%) and is therefore thought
to have a high contrast sensitivity but low acuity.
The dynamics of primate M retinal ganglion cells
Authors: BENARDETE ETHAN A. , KAPLAN EHUD
Published: July 2002

The retinal ganglion cells (RGCs) of the primate
form at least two classes—M and P—that differ
fundamentally in their functional properties. M cells have
temporal-frequency response characteristics distinct from
P cells (Benardete et al., 1992; Lee et al., 1994). In
this paper, we elaborate on the temporal-frequency responses
of M cells and focus in detail on the contrast gain control
(Shapley & Victor, 1979a,b). Earlier
data showed that the temporal-frequency response of M cells
is altered by the level of stimulus contrast (Benardete
et al., 1992). Higher contrast shifts the peak of the frequency-response
curve to higher temporal frequency and produces a phase
advance. In this paper, by fitting the data to a linear
filter model, the effect of contrast on the temporal-frequency
response is subsumed into a change in a single parameter
in the model. Furthermore, the model fits are used to predict
the response of M cells to steps of contrast, and these
predictions demonstrate the dynamic effect of contrast
on the M cells' response. We also present new data
concerning the spatial organization of the contrast gain
control in the primate and show that the signal that controls
the contrast gain must come from a broadly distributed
network of small subunits in the surround of the M-cell
receptive field.
The electroretinogram of the rhodopsin knockout mouse
Authors: TODA KAZUSHIGE , BUSH RONALD A. , HUMPHRIES PETER , SIEVING PAUL A.
Published: July 2002

The electroretinogram (ERG) of the rhodopsin knockout
(rho−/−) mouse of Humphries et al. (1997) (Humphries
et al., 1997) was studied for evidence of light-evoked
rod activity and to describe the cone function. The rho−/−
retina develops normal numbers of rod and cone nuclei,
but the rods have no outer segments, and no rhodopsin is
found by immunohistochemistry. The dark-adapted ERG threshold
was elevated 4.7 log units above wild-type (WT) control
mice, indicating that any residual rod responses were reduced
>50,000-fold, consistent with a complete functional
knockout. The dark-adapted rho−/− ERG had a
cone waveform, and the spectral sensitivity peaked near
510 nm for both dark-adapted and light-adapted conditions,
without evidence of a Purkinje shift. The light-adapted
ERG b-wave amplitude of young rho−/−
mice was the same as WT. The amplitude remained steady
up to postnatal day P47, but thereafter it declined to
only 1–2% by P80 when no cone outer segments remained.
Cone b-wave threshold of dark-adapted rho−/−
mice was −1.07 ± 0.39 log cd-s/m2
(n = 17), which is 1.27 log units more sensitive
than light-adapted thresholds against a rod-suppressing
Ganzfeld background of 1.61 log scotopic cd/m2.
This indicates that dark-adapted WT responses to still
dimmer stimuli are exclusively rod driven with minimal cone
intrusion. Above this cone threshold intensity, the dark-adapted
b-wave of WT will be a summation of rod and cone
responses. Threshold versus intensity (TVI) studies gave no
evidence of a rod influence on the mouse cone b-wave.
Evidence for a ganglion cell contribution to the primate
electroretinogram (ERG): Effects of TTX on the multifocal
ERG in macaque
Authors: HOOD D.C. , FRISHMAN L.J. , VISWANATHAN S. , ROBSON J.G. , AHMED J.
Published: July 2002

To assess the contribution of spiking inner retinal
neurons to the multifocal electroretinogram (ERG), recordings
were made from four monkeys (Macaca mulatta) before
and after intravitreal injections of tetrodotoxin (TTX).
TTX blocks all sodium-based action potentials and thus
terminates spiking activity of amacrine and ganglion cells.
TTX eliminated a large component from the control responses,
and this TTX-sensitive component was present as early as
10 ms after the stimulus. Before injection with TTX, the
103 focal ERG responses varied in waveform across the retina.
After TTX, the response waveforms were largely independent
of retinal position, indicating that it was primarily the
TTX-sensitive component of the control response that was
dependent upon retinal location. Given that retinal ganglion
cells compose a sizable proportion of the retinal elements
that produce action potentials, it is likely that part
of the TTX-sensitive component is due to the spiking activity
of these cells. Further, the systematic change in waveform
of the TTX-sensitive component with distance from the optic
nerve head suggests that part of the TTX-sensitive component
may originate from the activity of the ganglion cell axons.
Based on these findings, there is reason to be optimistic
that the multifocal technique can be employed to study
the effects of glaucoma and other diseases that affect
the inner retina.
Cell types and response timings in the medial interlaminar
nucleus and C-layers of the cat lateral geniculate nucleus
Authors: HUMPHREY ALLEN L. , MURTHY ADITYA
Published: July 2002

Previous evidence concerning the physiological
cell classes in the medial interlaminar nucleus (MIN) has
been conflicting. We reexamined the MIN using standard
functional tests to distinguish X-, Y- and W-cells. Discharge
patterns to flashing spots also were used to identify some
cells as lagged or nonlagged, as previously done for the
geniculate A-layers. Also, each cell's response timing
(latency and absolute phase) was measured from discharges
to a spot undergoing sinusoidal luminance modulation. Of
71 MIN cells, 48% were Y, 27% were W, 8% were X, and 17%
were unclassifiable. Lagged and nonlagged discharge profiles
were observed in each cell group, with 28% of all cells
being lagged. Lagged cells displayed a response suppression
and long latency to discharge following spot onset, and
a slow decay in firing at spot offset that was often preceded
by a transient discharge. These profiles were indistinguishable
from those of lagged cells in the A-layers. MIN cells also
were heterogeneous in response timing, displaying a range
of latency and absolute phase values similar to that in
the A-layers. We extended these analyses to 27 cells in
the geniculate C-layers. In layer C, 35% of cells were
Y, 10% were X, 25% were W, and 30% were unclassifiable.
About 11% had lagged profiles, and were X-cells or unclassifiable
cells. Layers C1 and C2 contained only W-cells and no lagged
profiles. The range of timings in the C-layers was somewhat
narrower than in the MIN. Overall, these results show that
the MIN contains a greater variety of functional cell classes
than heretofore appreciated. Further, it appears that mechanisms
which create different timing delays in the A-layers also
exist in the MIN and layer C. These timings may contribute
to direction selectivity in extrastriate cortex.
Effects of norepinephrine on the activity of visual neurons
in the superior colliculus of the hamster
Authors: ZHANG YI , MOONEY RICHARD D. , RHOADES ROBERT W.
Published: July 2002

Single-unit recording and micropressure ejection
techniques were used to test the effects of norepinephrine
(NE) on the responses of neurons in the superficial layers
(the stratum griseum superficiale and stratum
opticum) of the hamster's superior colliculus
(SC). Application of NE suppressed visually evoked responses
by ≥30% in 75% of 40 neurons tested and produced ≥30%
augmentation of responses in only 5%. The decrement in
response strength was mimicked by application of the α2
adrenoceptor agonist, p-aminoclonidine, the nonspecific
β agonist, isoproterenol, and the β1
agonist, dobutamine. These agents had similar effects on
responses evoked by electrical stimulation of the optic
chiasm and visual cortex. The α1 agonist,
methoxamine, augmented the light-evoked responses of 53%
of 49 SC cells by ≥30%, but had little effect on responses
evoked by electrical stimulation of optic chiasm or visual
cortex. The effects of adrenergic agonists upon the glutamate-evoked
responses of SC cells that were synaptically “isolated”
by concurrent application of Mg2+ were similar to those
obtained during visual stimulation. Analysis of effects of NE on
visually evoked and background activity indicated that application
of this amine did not significantly enhance signal-to-noise
ratios for most superficial layer SC neurons, and signal-to-noise
ratios were in some cases reduced. These results indicate
that NE acts primarily through α2 and β1
receptors to suppress the visual responses of SC neurons.
Activation of either of these receptors reduces the responses
of SC neurons to either of their two major visual inputs
as well as to direct stimulation by glutamate, and it would
thus appear that these effects are primarily postsynaptic.
Cloning and characterization of six zebrafish photoreceptor
opsin cDNAs and immunolocalization of their corresponding
proteins
Authors: VIHTELIC THOMAS S. , DORO CHRISTOPHER J. , HYDE DAVID R.
Published: July 2002

Zebrafish (Danio rerio) represents an
excellent genetic model for vertebrate visual system studies.
Because the opsin proteins are ideal markers of specific
photoreceptor cell types, we cloned six different zebrafish
opsin cDNAs. Based on pairwise alignments and phylogenetic
comparisons between the predicted zebrafish opsin amino
acid sequences and other vertebrate opsins, the cDNAs encode
rhodopsin, two different green opsins (zfgr1 and zfgr2),
a red, a blue, and an ultraviolet opsin. Phylogenetic analysis
indicates the zfgr1 protein occupies a well-resolved dendrogram
branch separate from the other green opsins examined, while
zebrafish ultraviolet opsin is closely related to the human
blue- and chicken violet-sensitive proteins. Polyclonal
antisera were generated against individual bacterial fusion
proteins containing either the red, blue, or ultraviolet
amino termini or the rod or green opsin carboxyl termini.
Immunolocalization on adult zebrafish frozen sections demonstrates
the green and red opsins are each expressed in different
members of the double cone cell pair, the blue opsin is
detected in long single cones, and the ultraviolet opsin
protein is expressed in the short single cones. In 120-h
postfertilization wholemounts, green, red, blue, and ultraviolet
opsin-positive cells are detected in an orderly arrangement
throughout the entire retina. The antibodies' photoreceptor-type
specificity indicates they will be useful for characterizing
both wild-type and mutant zebrafish retinas.
Neuronal responses to orientation and motion contrast in
cat striate cortex
Authors: KASTNER SABINE , NOTHDURFT HANS-CHRISTOPH , PIGAREV IVAN N.
Published: July 2002

Responses of striate neurons to line textures were
investigated in anesthetized and paralyzed adult cats.
Light bars centered over the excitatory receptive field
(RF) were presented with different texture surrounds composed
of many similar bars. In two test series, responses of
169 neurons to textures with orientation contrast (surrounding
bars orthogonal to the center bar) or motion contrast (surrounding
bars moving opposite to the center bar) were compared to
the responses to the corresponding uniform texture conditions
(all lines parallel, coherent motion) and to the center
bar alone. In the majority of neurons center bar responses
were suppressed by the texture surrounds. Two main effects
were found. Some neurons were generally suppressed by either
texture surround. Other neurons were less suppressed by
texture displaying orientation or motion (i.e. feature)
contrast than by the respective uniform texture, so that
their responses to orientation or motion contrast appeared
to be relatively enhanced (preference for feature contrast).
General suppression was obtained in 33% of neurons tested
for orientation and in 19% of neurons tested for motion.
Preference for orientation or motion contrast was obtained
in 22% and 34% of the neurons, respectively, and was also
seen in the mean response of the population. One hundred
nineteen neurons were studied in both orientation and motion
tests. General suppression was correlated across the orientation
and motion dimension, but not preference for feature contrast.
We also distinguished modulatory effects from end-zones
and flanks using butterfly-configured texture patterns.
Both regions contributed to the generally suppressive effects.
Preference for orientation or motion contrast was not generated
from either end-zones or flanks exclusively. Neurons with
preference for feature contrast may form the physiological
basis of the perceptual saliency of pop-out elements in
line textures. If so, pop-out of motion and pop-out of
orientation would be encoded in different pools of neurons
at the level of striate cortex.
Comparison of the responses of AII amacrine cells in the
dark- and light-adapted rabbit retina
Authors: XIN DAIYAN , BLOOMFIELD STEWART A.
Published: July 2002

We studied the light-evoked responses of AII amacrine
cells in the rabbit retina under dark- and light-adapted
conditions. In contrast to the results of previous studies,
we found that AII cells display robust responses to light
over a 6–7 log unit intensity range, well beyond
the operating range of rod photoreceptors. Under dark adaptation,
AII cells showed an ON-center/OFF-surround receptive-field
organization. The intensity–response profile of the
center-mediated response component followed a dual-limbed
sigmoidal function indicating a transition from rod to
cone mediation as stimulus intensities were increased.
Following light adaptation, the receptive-field organization
of AII cells changed dramatically. Light-adapted AII cells
showed both ON- and OFF-responses to stimulation of the
center receptive field, but we found no evidence for an
antagonistic surround. Interestingly, the OFF-center response
appeared first following rapid light adaptation and was
then replaced gradually over a 1–4 min period by
the emerging ON-center response component. Application
of the metabotropic glutamate receptor agonist APB, the
ionotropic glutamate blocker CNQX, 8-bromo-cGMP, and the
nitric oxide donor SNAP all showed differential effects
on the various center-mediated responses displayed by dark-
and light-adapted AII cells. Taken together, these pharmacological
results indicated that different synaptic circuits are
responsible for the generation of the different AII cell
responses. Specifically, the rod-driven ON-center responses
are apparently derived from rod bipolar cell synaptic inputs,
whereas the cone-driven ON-center responses arise from
signals crossing the gap junctions between AII cells and
ON-center cone bipolar cells. Additionally, the OFF-center
response of light-adapted AII cells reflects direct synaptic
inputs from OFF-center cone bipolar cells to AII dendritic
processes in the distal inner plexiform layer.
Alcohol does not affect visual contrast gain mechanisms
Authors: PEARSON PAULINE , TIMNEY BRIAN
Published: July 2002

It has been suggested that acetylcholine plays
a role in contrast discrimination performance and the regulation
of visual contrast gain (Smith, 1996). Since alcohol has
been shown to reduce levels of acetylcholine and contrast
sensitivity, the present study measured the effects of
alcohol on contrast discrimination and explored whether
the deficits could be explained as a consequence of reduction
in contrast gain. Detection thresholds and contrast increment
thresholds under placebo and alcohol (0.06% BAC) conditions
were measured in six volunteers. Alcohol was found to impair
both detection and discrimination of only high spatial
frequencies. However, when the base contrasts used in the
increment threshold task were equal multiples of detection
threshold, no alcohol-induced changes in increment thresholds
were obtained at any spatial frequency. We conclude that
alcohol impairs contrast discrimination performance but
that no change in contrast gain mechanisms need be postulated
to account for the data.
Development and regulation of substance P expression in
neurons of the tadpole optic tectum
Authors: TU SHICHUN , DEBSKI ELIZABETH A.
Published: July 2002

Activity-dependent synaptic plasticity is characteristic
of developing visual systems. Using the frog retinotectal
system, we investigated the extent to which afferent input
affects neurotransmitter expression in a target structure.
We have concentrated on a particular subpopulation of tectal
cells that is immunoreactive to substance P (SP). Early
in development, SP expression in tectal neurons was restricted
to the anterior lateral region of the tectum. As tadpoles
developed, this expression expanded into progressively
more posterior and medial regions in a manner that closely
followed the gradient of tectal maturation. At all times,
however, anterior and lateral tectal regions had a greater
percent of SP-like immunoreactive (SP-ir) cells than posterior
and medial ones. Horseradish peroxidase (HRP) labeling
of the retinal ganglion cell projection in conjunction
with SP immunocytochemistry demonstrated that innervation
by retinal ganglion cell terminals preceded the expression
of SP by tectal cells. This suggested that the optic nerve
may influence SP differentiation and/or expression. In
support of this idea, transection of the optic nerve resulted
in a decrease in SP expression in the deafferented tectal
lobe of tadpoles. This result, opposite to that seen previously
in the adult, also indicates that optic nerve–dependent
regulation of SP expression in the developing and mature
systems occurs through different pathways.
Vision in mice with neuronal redundancy due to inhibition
of developmental cell death
Authors: PORCIATTI VITTORIO , PIZZORUSSO TOMMASO , MAFFEI LAMBERTO
Published: July 2002

Transgenic mice overexpressing bcl-2,
due to inhibition of naturally occurring cell death, have
much larger brains and optic nerves as compared to wild-type
mice. Since developmental cell death is believed to exert
a crucial role in establishing the mature neural circuitry
and function, we asked the question of whether basic aspects
of vision were altered in bcl-2 mice. Local visually
evoked potentials (VEPs) in response to patterned stimuli
were recorded from the primary visual cortex. The representation
of the vertical meridian was displaced by about 15% in
the bcl-2 mouse, accounting for brain expansion.
However, visual acuity, contrast threshold, and response
latency were normal, indicating that compensatory mechanisms
can ensure normal basic properties of vision in spite of
marked neuronal redundancy.
Synaptic connectivity of two types of recoverin-labeled
cone bipolar cells and glutamic acid decarboxylase immunoreactive
amacrine cells in the inner plexiform layer of the rat
retina
Authors: CHUN MYUNG-HOON , KIM IN-BEOM , OH SU-JA , CHUNG JIN-WOONG
Published: July 2002

We investigated the synaptic connectivity of two
populations of recoverin-labeled bipolar cells and GABAergic
neurons in the inner plexiform layer (IPL) of the rat retina.
Two types of cone bipolar cells, type 2 and type 8, were
stained with anti-recoverin antibodies, and GABAergic neurons
were stained with anti-glutamic acid decarboxylase (GAD)
antibodies. Type 2 cone bipolar axons received synaptic
input from amacrine cell processes in 177 cases; among
these amacrine cell processes, 92 processes (52.0%) were
GAD-like immunoreactive. A total of 159 amacrine cell processes,
which are presynaptic to type 8 cone bipolar cells, were
observed. Among these processes, 117 processes (73.6%)
were GAD-like immunoreactive. The postsynaptic elements
at the ribbon synapses of recoverin-labeled cone bipolar
cells were observed in 482 processes. In both type 2 and
type 8 cone bipolar cells, the major output was to amacrine
cell processes. At the ribbon synapses of the type 2 cone
bipolar cells, 224 of the postsynaptic profiles were amacrine
cell processes, 97 processes (43.3%) were GAD-like immunoreactive.
In type 8 cone bipolar cells, 45 processes (30.2%) of 149
amacrine cell processes were GAD-like immunoreactive. Our
results provide morphological evidence that GABA is a major
transmitter involved in the visual processing of type 2
and 8 cone bipolar cells and GABA may have a stronger influence
on type 8 cone bipolar cells than type 2 cone bipolar cells
in the IPL of the rat retina.