bluuebunny/crossref_metadata_2025 huggingface dataset:
DERIVING THE EXACT DISCRETE ANALOG OF A CONTINUOUS TIME SYSTEM
Authors: McCrorie J. Roderick
Published: July 2002

The exact discrete model satisfied by equispaced data
generated by a linear stochastic differential equations
system is derived by a method that does not imply restrictions
on observed discrete data per se. The method involves integrating
the solution of the continuous time model in state space
form and a nonstandard change in the order of three types
of integration, facilitating the representation of the
exact discrete model as an asymptotically time-invariant
vector autoregressive moving average model. The method
applying to the state space form is general and is illustrated
using the prototypical higher order model for mixed stock
and flow data discussed by Bergstrom (1986, Econometric
Theory 2, 350–373).
Floristics and structure of the Pterocarpus officinalis swamp forest in Guadeloupe, Lesser Antilles
Authors: Imbert Daniel , Bonhême Ingrid , Saur Etienne , Bouchon Claude
Published: July 2002

Swamp forest covers c. 2600 ha of coastal wetlands in Guadeloupe. An inventory of all vascular plants was conducted together with a characterization of the main abiotic descriptors within seventeen 10-m × 40-m plots, systematically sampled throughout the forest. Girth at breast height (GBH) was measured for all trees ≥10 cm GBH. Four forest types were discriminated according to pH, clay content and redox potential of the soils. Among the 107 species recorded, lianas and epiphytes were as much represented as tree species (28%). However, no epiphytes were encountered at the canopy level where Pterocarpus officinalis (Papilionaceae) was the evenly dominant tree. Local hummock-hollow topography was responsible for an aggregated distribution of P. officinalis. This species exhibits several adaptative traits which may explain its dominance over all of the lowland swamp forests subjected to permanent waterlogging in the hurricane-prone Caribbean islands.
The importance of herbivore interactions for the dynamics of African savanna woodlands: an hypothesis
Authors: Koppel Johan Van De , Prins Herbert H. T.
Published: July 2002

Current hypotheses to explain dynamic transitions between savanna grasslands and woodlands in Africa focus on grazing by elephant or the influence of fire. Using a simple mathematical model, this paper argues that interactions between small herbivores such as impala or buffalo and large herbivores such as elephant or giraffe may provide a plausible alternative hypothesis. The interplay of competition and facilitation between these types of herbivores could explain transitions between grassland and woodland and vice versa. A review of the literature is presented in support of this hypothesis.
Constraint programming and maths programming
Authors: PUGET JEAN-FRANÇOIS , LUSTIG IRVIN
Published: July 2002

Maths programming (MP) and constraint programming (CP) are two techniques that are able to solve difficult industrial optimisation problems. The purpose of this paper is to compare them from an algorithmic and a modelling point of view. Algorithmic principles of each approach are described and contrasted. Some ways of combining both techniques are also introduced.
LANGUAGE CONTACT, VARIATION, AND CHANGE. Jussi Niemi,
Terence Odlin, and Janne Heikkinen (Eds.). Joensuu, Finland: University of Joensuu, 1998.
Pp. 286.
Authors: Winkler Elizabeth
Published: July 2002

The chapters of this book come from the 1997 Finnish Conference on Linguistics and the
Scandinavian Summer School on Language Diversity. A number of the contributions focus on
endangered languages, in particular, Ingrian Finnish. Hallamaa discusses developing appropriate
methodologies to study endangered languages and evaluate individual language proficiency.
Chapters by Koko and Riionheimo describe the loss of Ingrian through shift to Estonian. Ingrian
is, again, the topic for Savijiirvi, who compares and provides a detailed sociohistory of four
Balto-Finnic languages: Votian, Ingrian, Estonian, and Finnish. Duray writes about language
death, focusing on the extralinguistic factors that have caused a community-wide shift to Russian
by the Nganasan-speaking people.
CONTEMPORARY PERSPECTIVES ON THE ACQUISITION OF SPANISH.
VOL. 1: DEVELOPING GRAMMARS. VOL. 2: PRODUCTION, PROCESSING, AND
COMPREHENSION.Ana T. Pérez-Leroux and William R. Glass (Eds.).
Somerville, MA: Cascadilla Press, 1997. Vol. 1: Pp. 217. Vol. 2: Pp. 166. $42.00
paper.
Authors: Comajoan Llorenç
Published: July 2002

These two volumes contain a selection of 19 papers presented at the Penn State Conference
on the Acquisition of Spanish as a First or Second language held in October 1995.
Chain recurrence in flows on the Klein bottle
Authors: ALEXELLIS ATHANASSIOS , ATHANASSOPOULOS KONSTANTIN
Published: July 2002

In the classical Poincaré–Bendixson theory
the object of study are the limit sets of a continuous flow on the 2-sphere
S2 and the behaviour of the orbits near them
(see [7, 9]). In [2] the
second author proved that an assertion similar to the Poincaré–Bendixson
theorem is true in the wider class of the 1-dimensional invariant (internally)
chain recurrent continua of flows on S2. On the other
hand, it is known that among the closed 2-manifolds, the 2-sphere S2,
the projective plane RP2 and the
Klein bottle K2 are the only ones for which the
Poincaré–Bendixson theorem is true
(see [1, 8, 11]).

The motivation of the present paper was to examine to what extent the main
results of [2] carry over to flows on RP2
and K2. A first attempt to study chain
recurrent sets of flows on closed 2-manifolds other than the 2-sphere
was [3]. As one
expects, the results of [2] carry over easily to
RP2, since chain recurrence behaves
well with respect to regular covering maps of compact manifolds, as we show in
Section 3. The situation with K2 is quite different,
since it is doubly covered by the
2-torus T2, where we have no Poincaré–Bendixson
theorem. Actually, the Poincaré–Bendixson theorem for
1-dimensional invariant chain recurrent continua of flows on
K2 is not true. For example, identifying
suitably the boundary periodic orbits of
a 2-dimensional Reeb flow on a closed annulus (see
[7, chapter III, 2·6]) we get a
flow on K2 with a 1-dimensional invariant chain
recurrent continuum consisting of
the unique periodic orbit and another orbit, which spirals against it in positive and
negative time. As we prove in Theorem 4·4, this situation, or concatenations of it,
is the only one where the Poincaré–Bendixson theorem for 1-dimensional invariant
chain recurrent continua of flows on K2 is not
true. Then, we are concerned with
the topological structure of the 1-dimensional chain components of a flow on
K2 with finitely many singularities. In
Proposition 4·6 we find when such a set consists
of finitely many orbits and is homeomorphic to a finite graph. An example shows
that the hypothesis of Proposition 4·6 is essential. Finally,
in Theorem 4·9 we give a
description of the structure of the 1-dimensional chain components of a
flow on K2 with finitely many singular points.
GPS Receiver Performance Enhancement via Inertial Velocity Aiding
Authors: Jwo Dah-Jing
Published: July 2002

An integrated GPS/INS navigation system can employ inertial velocity information to
produce a more robust system. For a stand-alone GPS receiver, decreasing the receiver
tracking loop bandwidth reduces the probability of losing lock in a jamming or interference
environment if vehicle dynamics are low. However, reduced bandwidth increases tracking
errors when dynamics are present. Beyond a certain limit, it causes a serious degradation in
the dynamic tracking loop performance. Providing inertial velocity aiding to the receiver
tracking loops is an effective and popular treatment to help resolve this problem. In this
paper, performance of the GPS receiver tracking loops using inertial velocity aiding will be
investigated. Different types of tracking loops, from 1st to 3rd order, are covered. Following
the discussion of the system architecture and derivation of the related transfer functions for
the tracking loops, both with and without aiding, the system performance, including
transient response, steady-state error, and noise bandwidth is evaluated.
Civil Marine Radar – A Review and a Way Ahead
Authors: Williams P. D. L.
Published: July 2002

Civil Marine Radar (CMR) is now a mature instrument
of some 50 years steady development.
Following a short history, more to provide benchmarks of achievement than
to satisfy
historians, this paper examines what will drive the future
development of CMR. The answer
may not follow recent developments, but may well be the result
of a fresh maritime modus
operandi to fulfil the navigation, collision avoidance and safe passage

needs of all types of craft
operating in all types of water with different pressures and
Operational Requirements (ORS).
Having postulated fresh ORS, suggestions are made on how best
to fulfil them
in a logical and cost-effective manner.
GPS in Agriculture – A Growing Market!
Authors: Stafford J. V.
Published: July 2002

This paper, and the paper which follows it, were first presented
at the IBC '98
Conference ‘Space-Based Navigation Industry’, which was held
in London,
11–12 June 1998.

In conventional arable agriculture, position within the field was
usually irrelevant! However,
the advent of precision agriculture, wherein inputs are targeted according
to locally-determined requirements within the field, has opened up a potentially large
market for GPS.
Indeed, it was the availability of GPS which permitted the development
and implementation
of precision agriculture – a concept which holds the promise of significant
economic and
environmental benefits to the farmer. This paper indicates the technical
requirements for
GPS and presents three case studies where a positioning system is required.
A comparison of the enforcement of access restrictions between Xishuangbanna Nature Reserve (China) and Khao Yai National Park (Thailand)
Authors: ALBERS HEIDI J. , GRINSPOON ELISABETH
Published: July 2002

Given limited budgets to enforce access restrictions, protected area (PA) managers and non-governmental organizations (NGOs) in developing countries employ a range of policy instruments to conserve the area's natural resources. Natural characteristics of the PA combine with the managers' enforcement activities and other policy instruments to create a set of incentives to which local people respond in making decisions about extracting resources from the PA. The different management approaches employed in the Xishuangbanna Nature Reserve (XNR; China) and the Khao Yai National Park (KYNP; Thailand) and the reaction to the incentives which they create are compared. KYNP managers use policing and punishment mechanisms, in conjunction with limited NGO-supported income-generation projects, to deter resource use. In contrast, XNR managers rely on extensive cooperation with local people and trade-offs between current resource degradation and increased rural incomes.

As predicted by the economic enforcement literature, rural people respond to the threat of punishment, and its reduction of the expected benefit of an illegal activity, by reducing that activity, but may undertake socially-costly avoidance activities to avoid punishment. This literature also correctly predicts that XNR managers will concentrate less on pure enforcement than KYNP managers because, as a result of a difference in government mandates, the XNR managers consider the value of the extracted products and the non-PA productivity in their decisions while the KYNP managers do not. In both PAs, rural people's actions affect the quality of resource conservation. In KYNP, natural characteristics and the policing activities deter resource extraction and encroachment in the central core of the Park. Even NGO projects, however, have not controlled extraction, and even agricultural encroachment, in the outer third of the Park, which has caused over-extraction of some resources and has left a ring of highly-degraded land. In contrast, XNR's cooperative management approach has generated more control over the amount and the spatial configuration of resource degradation. XNR's control, however, comes at the cost of reduced area and level of current conservation.
Optimal turning gait of a six-legged robot using a GA-fuzzy
approach
Authors: PRATIHAR DILIP KUMAR , DEB KALYANMOY , GHOSH AMITABHA
Published: July 2002

This paper describes a new method for generating
the turning-gait of a six-legged robot using a combined
genetic algorithm (GA)-Fuzzy approach. The main drawback
of the traditional methods of gait generation is their
high computational load. Thus, there is still a need for
the development of a computationally tractable algorithm
that can be implemented online to generate stable gait
of a multilegged robot. In the proposed genetic-fuzzy
system, the fuzzy logic controllers (FLCs) are used to
generate the stable gait of a hexapod and a GA is used
to improve the performance of the FLCs. The effectiveness
of the proposed algorithm is tested on a number of turning-gait
generation problems of a hexapod that involve translation
as well as rotation of the vehicle. The hexapod will have
to take a sharp circular turn (either clockwise or counter-clockwise)
with minimum number of ground legs having the maximum average
kinematic margin. Moreover, the stability margin should
lie within a certain range to ensure static stability of
the vehicle. Each leg of a six-legged robot is controlled
by a separate FLC and the performance of the controllers
is improved by using a GA. It is to be noted that the actual
optimization is done off-line and the hexapod can use these
optimized FLCs to navigate in real-world scenarios. As
an FLC is computationally less expensive, the proposed
algorithm will be faster compared with the traditional
methods of gait-generation, which include both graphical
as well as analytical methods. The GA-tuned FLCs are found
to perform better than the author-defined FLCs.
Feline calicivirus as a model system for heat inactivation
studies of small round structured viruses in shellfish
Authors: SLOMKA M. J. , APPLETON H.
Published: July 2002

Commercial heat treatment procedures for molluscan shellfish
are based on data obtained for
the inactivation of hepatitis A virus (HAV) in cockles. However, the most
frequently reported
illness associated with consumption of bivalve molluscs is gastroenteritis
caused by small round
structured viruses (SRSVs) of the Norwalk group. Conditions for inactivation
of SRSVs are
unknown. In this study a feline calicivirus was used as a model for the
SRSV group and
conditions for its heat inactivation determined. Experiments showed that
feline calicivirus is
more readily inactivated in shellfish than HAV, and confirmed that current
heating
recommendations to the UK shellfish industry are adequate. A reverse transcription
polymerase
chain reaction (RT-PCR) assay for the detection of calicivirus in shellfish
was developed and
results compared with isolation in cell culture. The RT-PCR detected virus
in some samples
that failed to yield virus on culture. This has important implications
if molecular virology
techniques are to be used in the design and monitoring of shellfish treatment
procedures and
for routine testing of food samples.
Clonality of Campylobacter sputorum bv. paraureolyticus
determined by macrorestriction profiling and biotyping, and
evidence for long-term persistent infection in cattle
Authors: ON S. L. W. , ATABAY H. IBRAHIM , CORRY J. E. L.
Published: July 2002

Eighteen strains of Campylobacter sputorum bv. paraureolyticus
(isolated over a 12-month
period from seven dairy cows contained in a single herd) were examined
by resistotyping, and
macrorestriction profiling using pulsed field gel electrophoresis (PFGE).
The resistotypes of
these strains were identical, although repeat testing indicated resistance
to metronidazole was
not a reliable trait for typing purposes. Five SmaI-derived genotypes
were identified among the
18 strains. In 5 of 7 cows, isolates obtained from the same animal, but
from different time
periods, were genotypically indistinguishable, indicating persistence of
infection.
Macrorestriction profiles of 5 strains representing the 5 SmaI
genotypes and 8 other strains of
C. sputorum from various sources, were prepared using 4 endonucleases
(SmaI, SalI, BamHI
and KpnI). The only other strain of C. sputorum bv. paraureolyticus
examined (a Canadian
isolate from human faeces), was found to have a SmaI macrorestriction
profile identical with
one of the five clones isolated from the cattle. Moreover, SalI
and BamHI profiles of all bv.
paraureolyticus strains were similar, while digestion with KpnI
was not observed. By contrast,
the seven strains of C. sputorum bv. sputorum yielded various
macrorestriction profiles with all
the enzymes used, and features distinguishing the two biovars studied could
be identified. This
study indicates that C. sputorum can persist in cattle for at
least 12 months and exhibits a
clonal population genetic structure.
Serpulina pilosicoli, waterbirds and water: potential sources

of infection for humans and other animals
Authors: OXBERRY S. L. , TROTT D. J. , HAMPSON D. J.
Published: July 2002

Serpulina pilosicoli was isolated from 8 of 43 (19%) faecal

specimens obtained from feral
waterbirds sampled around a small lake at Perth Zoological Gardens, Western
Australia, and
from 3 of 7 (43%) samples of the lake water. The organism was only isolated
from 1 of 204
(0·5%) samples from captive birds and animals in the zoological

collection. Multilocus enzyme
electrophoresis analysis of the isolates showed that they were
genetically diverse, and none had
identical electrophoretic profiles as those previously obtained from human
beings, dogs, pigs
and other avian species. To determine the survival time of
S. pilosicoli in water, cells of strain
1648 were seeded into lake and tap water, and incubated at 4, 25 and 37°C.
The organism
could be recultured from lake water for up to 66 days at
4°C, and for 4 days at 25°C. A
healthy human volunteer who drank water seeded with S. pilosicoli
strain Wes B became
colonized, and developed abdominal discomfort and headaches. Contamination
of water by
faeces may represent a source of S. pilosicoli infection for both
humans and animals.
Risk factors of acute diarrhoea in summer – a nation-wide French case-control study
Authors: YAZDANPANAH Y. , BEAUGERIE L. , BOËLLE P. Y. , LETRILLIART L. , DESENCLOS J. C. , FLAHAULT A.
Published: July 2002

The aim of this study was to identify risk factors for acute diarrhoea (AD) during the summer
in France. A matched case-control study was conducted at a national level among patients of
500 general practitioners (GPs). From July to September 1996, 468 case-control pairs were
included. Cases were more likely than controls (i) to live away from their main residence (OR
3·0; 95% CI 1·6–5·7), (ii) to have returned from a country at high risk of AD (OR 4·6; CI
0·9–23·1), and (iii) to have been in contact with a case of AD (OR 2·0; CI 1·3–3·1). A
significantly decreased risk of AD was found for consumption of well-cooked chicken (OR 0·5;
CI 0·3–0·8) and raw or undercooked home-made egg-containing products (OR 0·6; CI 0·4–0·8).
These findings suggest that travel to high-risk areas, or travel within France, and being in
contact with a case of AD, are risk factors for the occurrence of AD in summer in France.
Differential contributions of magnocellular and parvocellular pathways to
the contrast response of neurons in bush baby primary visual cortex (V1)
Authors: ALLISON JOHN D. , MELZER PETER , DING YUCHUAN , BONDS A.B. , CASAGRANDE VIVIEN A.
Published: July 2002

How neurons in the primary visual cortex (V1) of
primates process parallel inputs from the magnocellular
(M) and parvocellular (P) layers of the lateral geniculate
nucleus (LGN) is not completely understood. To investigate
whether signals from the two pathways are integrated in
the cortex, we recorded contrast-response functions (CRFs)
from 20 bush baby V1 neurons before, during, and after
pharmacologically inactivating neural activity in either
the contralateral LGN M or P layers. Inactivating the M
layer reduced the responses of V1 neurons (n =
10) to all stimulus contrasts and significantly elevated
(t = 8.15, P < 0.01) their average
contrast threshold from 8.04 (± 4.1)% contrast to
22.46 (± 6.28)% contrast. M layer inactivation also
significantly reduced (t = 4.06, P <
0.01) the average peak response amplitude. Inactivating
the P layer did not elevate the average contrast threshold
of V1 neurons (n = 10), but significantly reduced
(t = 4.34, P < 0.01) their average
peak response amplitude. These data demonstrate that input
from the M pathway can account for the responses of V1
neurons to low stimulus contrasts and also contributes
to responses to high stimulus contrasts. The P pathway
appears to influence mainly the responses of V1 neurons
to high stimulus contrasts. None of the cells in our sample,
which included cells in all output layers of V1, appeared
to receive input from only one pathway. These findings
support the view that many V1 neurons integrate information
about stimulus contrast carried by the LGN M and P pathways.
The role of NMDA channels in rabbit retinal directional selectivity
Authors: TJEPKES DARREL S. , AMTHOR FRANKLIN R.
Published: July 2002

It has been previously demonstrated that the majority
of the glutamatergic input to directionally selective (DS)
ganglion cells in the rabbit retina is mediated by NMDA
receptors. To examine whether NMDA channels have any role
in directional selectivity, we eliminated magnesium from
the superfusion medium to prevent the magnesium block of
the channels at hyperpolarized membrane potentials. During
superfusion in magnesium-free media, the response to null-direction
motion increased to the level of the response to preferred-direction
motion. This effect was specifically mediated by NMDA channels
because subsequent blocking of the NMDA channels with AP7
restored directional selectivity. We also tested whether
the increase in the null-direction response in magnesium-free
medium was due to an increased release of acetylcholine
from the cholinergic amacrine cells, rather than an effect
on the DS ganglion cells themselves, by blocking acetylcholine
transmission with d-tubocurarine during superfusion with
the magnesium-free medium. During zero-magnesium superfusion,
d-tubocurarine reduced both the preferred- and null-direction
responses of DS ganglion cells but did not restore directional
selectivity. These findings suggest that null-direction
motion normally causes portions of the dendritic membrane
of the directionally selective ganglion cell to be maintained
at a sufficiently negative potential that the NMDA channels
are blocked by magnesium ions. This result is discussed
in terms of several models for the mechanisms of directional
selectivity.
Localization of heme oxygenase-2 and modulation of cGMP
levels by carbon monoxide and/or nitric oxide in the retina
Authors: CAO LUXIANG , BLUTE TODD A. , ELDRED WILLIAM D.
Published: July 2002

Heme oxygenase-2 (HO-2) synthesizes carbon monoxide
(CO), a modulator of soluble guanylate cyclase (sGC). To
examine this signal transduction pathway in the retina,
we immunocytochemically localized HO-2, and investigated
the effects of CO on cGMP levels. In turtle, HO-2-like
immunoreactivity (-LI) was in all photoreceptors, some
amacrine cells, and in numerous bipolar and ganglion cells.
HO-2-LI colocalized with sGC activity in many cells. In
rat, HO-LI was found only in the inner retina, in ganglion
and amacrine cells. In turtle, stimulation with CO alone
primarily increased cGMP-LI in bipolar cells in the visual
streak. Stimulation with a combination of CO and nitric
oxide (NO) dramatically increased cGMP-LI throughout the
retina, in comparison to the smaller increases seen with
NO or CO alone. These data suggest that CO is an endogenous
modulator of the sGC/cGMP signaling pathway in many retinal
neurons, and can dramatically amplify NO-stimulated increases
in cGMP.
Visual signals used in time-interval discrimination
Authors: WESTHEIMER GERALD
Published: July 2002

Thresholds for the detection of differences in the
duration of visual stimuli were determined for a variety
of programs of stimulus onset and offset. Performance suffers
when a time interval begins with an ON step and ends with
another ON stimulus, compared to the standard ON–OFF
stimulation, but the decrement is reversed when the light
is ramped down to background during the interval. Neither
the magnocellular nor the parvocellular streams can be
excluded because there is relatively little impairment
of duration discrimination when the stimulus has low contrast
or is heterochromatic at isoluminance. Performance at a
variety of intensity levels suggests that sustained neural
firing in an early stage of visual processing provides
a background activity, which prevents good temporal precision
of signals.
Color-opponent responses of small and giant bipolar cells
in the carp retina
Authors: SHIMBO KIYOSHI , TOYODA JUN-ICHI , KONDO HIROAKI , KUJIRAOKA TORU
Published: July 2002

The physiological and morphological properties
of color-opponent bipolar cells in the carp retina were
studied. Fifty nine OFF-center bipolar cells and 63 ON-center
bipolar cells out of about 500 total bipolar cells recorded
showed color-opponent responses. The OFF-center color-opponent
bipolar cells were classified into three subgroups according
to their spectral and spatial responses. Fifty OFF-center
color-opponent cells responded with depolarization to a
blue light spot and with hyperpolarization to a red spot
in the receptive-field center. The polarity of the surround
response was opposite to that of center response at each
wavelength. Therefore these cells were classified as OFF
double-opponent cells (OFF-DO). Eight cells responded with
hyperpolarization to a blue and green spot and with depolarization
to a red spot. The surround responses of those cells were
depolarizing at any wavelength (R+G−
cell). One responded with hyperpolarization to a blue and
red spot and with depolarization to a green spot. The surround
response showed a different spectral characteristic from
that of the center response. It responded with depolarization
to a blue and green annulus and with hyperpolarization
to a red annulus (R−G+B−
cell). The ON-center color-opponent bipolar cells were
similarly classified into three subgroups. Sixty of ON-center
color-opponent cells were the double color-opponent type
(ON-DO cell), showing the responses of opposite polarity
to the OFF-DO cells. Two cells were classified as
R−G+ cell, and one cell as
R+G−B+ cell. Both OFF-
and ON-DO cells were identified by their morphology as Cajal's
giant bipolar cells, and R+G−,
R−G+,
R−G+B−,
and R+G−B+ cells
as Cajal's small bipolar cells. The analysis of the
latency and the ionic mechanisms of their responses suggest
that DO cells under light-adapted conditions receive direct
inputs from long-wavelength (red) cones, RG cells from
middle-wavelength (green) cones, and RGB cells from short-wavelength
(blue) cones. Possible mechanisms of the opponent inputs
to these bipolar cells are discussed.
Photoreceptor types and distributions in the retinae of
insectivores
Authors: PEICHL LEO , KÜNZLE HEINZ , VOGEL PETER
Published: July 2002

The retinae of insectivores have been rarely studied, and
their photoreceptor arrangements and expression patterns of
visual pigments are largely unknown. We have determined
the presence and distribution of cones in three species
of shrews (common shrew Sorex araneus, greater
white-toothed shrew Crocidura russula, dark forest
shrew Crocidura poensis; Soricidae) and in the
lesser hedgehog tenrec Echinops telfairi (Tenrecidae).
Spectral cone types were identified and quantified in flattened
whole retinae by antisera/antibodies recognizing the
middle-to-long-wavelength-sensitive (M/L-)cone opsin and the
short-wavelength-sensitive (S-)cone opsin, respectively. A
combination of immunocytochemistry with conventional histology
was used to assess rod densities and cone/rod ratios. In all
four species the rods dominate at densities of about
230,000–260,000/mm2. M/L- and S-cones are
present, comprising between 2% of the photoreceptors in the
nocturnal Echinops telfairi and 13% in Sorex
araneus that has equal diurnal and nocturnal activity
phases. This suggests dichromatic color vision like in many
other mammals. A striking feature in all four species are
dramatically higher S-cone proportions in ventral than in
dorsal retina (0.5% vs. 2.5–12% in Sorex,
5–15% vs. 30–45% in Crocidura poensis,
3–12% vs. 20–50% in Crocidura russula,
10–30% vs. 40–70% in Echinops). The
functional and comparative aspects of these structural findings are
discussed.
Thalamic control of cat area-18 supragranular layers: Simple
cells, complex cells, and cells projecting to the lateral
suprasylvian visual area
Authors: LEE CHOONGKIL , WEYAND THEODORE G. , MALPELI JOSEPH G.
Published: July 2002

The goal of this study was to determine the effects
of inactivating layer A or the C layers of the cat lateral
geniculate nucleus on the supragranular layers of area
18, including cells antidromically activated from the lateral
suprasylvian visual area (LS). Isolated cells were visually
driven via the contralateral eye while the retinotopically
corresponding regions of layer A or, in some cases, the
C layers were reversibly inactivated with injections of
cobaltous chloride. Simple cells were frequently encountered
and were on average more dependent upon layer A than were
complex cells, a result qualitatively similar to that found
previously in area 17 (Malpeli, 1983; Malpeli et al., 1986).
However, the influence of the C layers on area 18 was much
more apparent than for area 17. In area 18, as in area
17, the dependence of simple cells on particular geniculate
layers appears to follow the terminal patterns of the major
direct geniculate inputs. Those simple cells most dependent
on layer A were located in lower layer 3. Simple cells
in upper layer 3, like complex cells, showed little dependence
on layer A, but were strongly dependent upon the C layers.
All cells antidromically activated from LS were simple
cells with rapidly conducting axons. They had, on average,
the same moderately strong dependence on layer A as the
patches of LS receiving area 18 input (Lee et al., 1997),
supporting the conclusion that the influence of layer A
in these patches is largely transmitted via association
inputs from area 18. These results demonstrate that simple
cells play a major role in association pathways.
Diurnal variation in the b-wave implicit time of
the human electroretinogram
Authors: HANKINS M.W. , JONES R.J.M. , RUDDOCK K.H.
Published: July 2002

Photopic electroretinograms (ERGs) elicited by
light flashes were recorded for three normal human subjects
who were exposed, throughout, to natural ambient light
cycles over 24-h day–night periods. ERGs were recorded
either with the adaptation state of the eyes maintained
at the level set by the natural ambient lighting, or after
10 min dark adaptation. The amplitudes and implicit times
of both the a- and b-wave components
of the ERG were examined and of these, only the b-wave
implicit time exhibited significant diurnal variation,
such that the nighttime values were 20–40% greater
than those recorded during daytime. Such diurnal variations
were observed under both recording conditions and cannot,
therefore, be attributed to diurnal changes in the adaptation
state of the cone photoreceptors. ERGs were recorded at
midday and midnight during 24-h exposure to the natural
light cycle, but during the recording period, the short-term
adaptation state of the eye was controlled by exposure
to rod saturating background field, so that visual sensitivity
was the same at both recording times. The b-wave
implicit times recorded at midnight were, nonetheless,
greater than those recorded at midday. This difference
is not, therefore, determined by the short-term state of
retinal adaptation, but reflects long-term light history.
Measurements performed under 24-h continuous light exposure
showed no variation in the b-wave implicit time,
whereas some measurements made during extended dark adaptation
provided limited evidence for implicit time changes. By
controlling the wavelengths to which the eye was exposed
during the daylight phase of the diurnal cycle, it was
shown that the shifts in b-wave implicit time
associated with the change from dark to light are triggered
by the rod system, although they are most clearly observed
in the cone-dominant responses to long-wavelength light.
The results demonstrate a diurnal variation in the temporal
responses of the post-photoreceptoral cone pathways of
the human retina, which is triggered by activation of the
rod photoreceptors.
Localization of protein kinase C to UV-sensitive photoreceptors
in the mouse retina
Authors: WIKLER K.C. , STULL D.L. , REESE B.E. , JOHNSON P.T. , BOGENMANN E.
Published: July 2002

The present study has identified a population of
cone photoreceptors in the murine retina that are uniquely
immunoreactive for protein kinase C (PKC). Wavelength-sensitive
cone subtypes are segregated along the dorso-ventral axis
in the mouse retina with ventral retina occupied exclusively
by ultraviolet wavelength-sensitive (UVWS) cones, and dorsal
retina dominated by middle wavelength-sensitive cones.
PKC-positive cones are found primarily in the ventral retina,
and double-label immunocytochemistry using a short wavelength-sensitive
opsin antibody confirms that they specifically correspond
to the UVWS cone subtype. The PKC antibody, as documented
in other mammals, also identifies rod bipolar cells in
the mouse retina. UVWS cones and bipolar cells have previously
been shown to share transcriptional regulatory elements,
as observed in transgenic mice encoding a portion of the
human SWS-opsin promoter controlling the lacZ
reporter gene. In such mice, the transgene product, β-galactosidase,
is expressed in populations of both cones and bipolar cells.
The present study confirms that lacZ-expressing
photoreceptors are indeed PKC-positive photoreceptors,
but that the lacZ-expressing bipolar cells are
not the PKC-positive rod bipolar cells. These cells must
correspond to a type of cone bipolar cell.
Threshold fluctuations on temporally modulated backgrounds:
A possible physiological explanation based upon a recent
computational model
Authors: HOOD D.C. , GRAHAM N.
Published: July 2002

When a temporally fluctuating background is rapidly
modulated (e.g. 30 Hz), the threshold variation of a superimposed
flash (the probe) is approximately sinusoidal and in phase
with the stimulus. But, with low rates of sinusoidal modulation
(e.g. 1 Hz), the threshold variation is distinctly nonsinusoidal
in shape. The bases of these aspects of the data, as well
as an unmodulated, dc, threshold elevation, are poorly
understood. Here 30-Hz and 1-Hz conditions are simulated
using a new model of light adaptation (Wilson, 1997). By
assuming that the OFF pathway is twice as sensitive as
the ON pathway, the model correctly captured the key aspects
of both conditions. The results suggest that the 1-Hz data
are mediated by a mixture of ON and OFF pathways while
the 30-Hz data are largely mediated by the OFF pathway.
The probe thresholds on the 30-Hz background appear approximately
sinusoidal and approximately in phase with the background
stimulus. A number of factors contribute to this deceptively
simple observation.
UV responses in the retina of the turtle
Authors: VENTURA D.F. , de SOUZA J.M. , DEVOE R.D. , ZANA Y.
Published: July 2002

To study processing of UV stimuli in the retina
of the turtle, Trachemys dorbignii, we recorded
intracellular responses to spectral light from 89 cells:
54 horizontal (47 monophasic, five (R/G) biphasic and two
(Y/B) triphasic), 14 bipolar, 12 amacrine, and nine ganglion
cells. Spectral sensitivities were measured with monochromatic
flashes or with the dynamic constant response method in
dark or chromatic adapted states. Stray light and second-order
harmonics were also measured. (1) All cells responded to
UV stimuli, although none had maximum sensitivity in the
UV. (2) Most horizontal, bipolar, and amacrine cells had
red-peaked spectral sensitivities. (3) Red adaptation of
all monophasic horizontal cells indicated a single red
input, except one that had additional peaks in the blue
and UV. (4) Responses of biphasic and triphasic horizontal
cells to UV light were always hyperpolarizing. Opposition
between hyperpolarizing and depolarizing responses at long
wavelengths indicates that UV responses were not due to
the beta band of red receptors. (5) An unstained spectrally
opponent bipolar cell hyperpolarized in the center to green
light and antagonistically depolarized in the surround
to UV, blue, and green flashes, but hyperpolarized to red.
(6) All dark-adapted amacrine cells were red-peaked monophasic
cells, but red adaptation broadened their spectral-sensitivity
curves or displaced their peaks. An A15, an A18, and an
A24 wide-field amacrine cell were stained. (7) A G15 bistratified
ganglion cell is shown here for the first time to be spectrally
opponent. This UVB/RG cell depolarized to UV and blue and
hyperpolarized to red and green. It differs from previously
reported turtle ganglion cells in being color opponent
in the entire field, not only in the surround, and in showing
spatial opponency.
TTX attenuates surround inhibition in rabbit retinal ganglion
cells
Authors: TAYLOR W. ROWLAND
Published: July 2002

Patch-clamp recordings were made from ganglion
cells in an in vitro dark-adapted rabbit retina
preparation. Cells were stimulated by images generated
on a computer monitor and focussed onto the photoreceptors.
Excitatory inward currents were recorded in response to
spot stimuli centered on the somas of the recorded cells.
Center illumination of on-brisk-transient cells produced
large transient excitatory postsynaptic currents (EPSCs)
which were invariably followed by a small steady-state
inward component. Illumination of a centered annulus failed
to elicit the transient EPSC. Simultaneous illumination
of the annulus and the center spot blocked the large transient
EPSC, consistent with activation of an inhibitory surround.
Application of tetrodotoxin (TTX), which blocks sodium-dependent
action potentials, also blocked the surround inhibition
in ON-brisk transient cells as well as some other classes
of ganglion cells. It is concluded that, in some ganglion
cell classes, the surround is generated largely through
the activity of spiking neurons, and it is suggested that
the amacrine cells in the inner plexiform layer are involved.
Balanced interactions in ganglion-cell receptive fields
Authors: GRANDA A.M. , DEARWORTH J.R. , SUBRAMANIAM B.
Published: July 2002

Receptive fields of retinal ganglion cells in turtle
have excitatory and inhibitory components that are balanced
along the dimensions of wavelength, functional ON and OFF
responses, and spatial assignments of center and surround.
These components were analyzed by spectral light adaptations
and by the glutamate agonist, 2-amino-4-phosphonobutyric
acid (APB). Extracellular recordings to stationary and
moving spots of light were used to map changes in receptive
fields. ON spike counts minus OFF spike counts, derived
from flashed stationary light spots, quantified
functional shifts by calculating normalized mean response
modulations. The data show that receptive fields are not
static, but rather are dynamic arrangements which depend
on linked, antagonistic balances among the three dimensions
of wavelength, ON and OFF response functions, and center/surround
areas.
Ganglion cells of a short-wavelength-sensitive cone pathway
in New World monkeys: Morphology and physiology
Authors: SILVEIRA LUIZ CARLOS L. , LEE BARRY B. , YAMADA ELIZABETH S. , KREMERS JAN , HUNT DAVID M. , MARTIN PAUL R. , GOMES FRANCINALDO L.
Published: July 2002

We have studied the morphology and physiology of
retinal ganglion cells of a short-wavelength-sensitive
cone (SWS-cone) pathway in dichromatic and trichromatic
New World anthropoids, the capuchin monkey (Cebus apella)
and tufted-ear marmoset (Callithrix jacchus).
In Old World anthropoids, in which males and females are
both trichromats, blue-ON/yellow-OFF retinal ganglion cells
have excitatory SWS-cone and inhibitory middle- and long-wavelength-sensitive
(MWS- and LWS-) cone inputs, and have been anatomically
identified as small-field bistratified ganglion cells (SB-cells)
(Dacey & Lee, 1994). Among retinal ganglion cells of
New World monkeys, we find SB-cells which have very similar
morphology to such cells in macaque and human; for example,
the inner dendritic tree is larger and denser than the
outer dendritic tree. We also find blue-on retinal ganglion
cells of the capuchin to have physiological responses strongly
resembling such cells of the macaque monkey retina; for
example, responses were more sustained, with a gentler
low frequency roll-off than MC-cells, and no evidence of
contrast gain control. There was no difference between
dichromatic and trichromatic individuals. The results support
the view that SWS-cone pathways are similarly organized
in New and Old World primates, consistent with the hypothesis
that these pathways form a phylogenetically ancient color
system.
Light and electron microscopical analysis of nitric oxide
synthase-like immunoreactive neurons in the rat retina
Authors: CHUN MYUNG-HOON , OH SU-JA , KIM IN-BEOM , KIM KEUN-YOUNG
Published: July 2002

We have investigated the morphology of the NOS-like
immunoreactive neurons and their synaptic connectivity
in the rat retina by immunocytochemistry using antisera
against nitric oxide synthase (NOS). In the present study,
several types of amacrine cells were labeled with anti-NOS
antisera. Type 1 cells had large somata located in the
inner nuclear layer (INL) with long and sparsely branched
processes ramifying mainly in stratum 3 of the inner plexiform
layer (IPL). Somata of type 2 cells with smaller diameters
were also located in the INL. Their fine processes branched
mostly in stratum 3 of the IPL. A third population showing
NOS-like immunoreactivity was a class of displaced amacrine
cells in the ganglion cell layer (GCL). Their soma size
was similar to that of the type 1 cells; however, their
processes stratified mainly in strata 4 and 5 of the IPL.
Labeled neurons were evenly distributed throughout the
retina, and the mean densities were 57.0 ± 9.7 cells/mm2
for the type 1 cells, 239.3 ± 43.4 cells/mm2
for the type 2 cells and 121.2 ± 27.5 cells/mm2
cells for the displaced amacrine cells. The synaptic connectivity
of NOS-like immunoreactive amacrine cells was identified
in the IPL by electron microscopy. NOS-labeled amacrine
cell processes received synaptic input from other amacrine
cell processes and bipolar cell axon terminals in all strata
of the IPL. The most frequent postsynaptic targets of NOS-immunoreactive
amacrine cells were other amacrine cell processes. Ganglion
cell dendrites were also postsynaptic to NOS-like immunoreactive
neurons in both sublaminae of the IPL. Synaptic outputs
onto bipolar cells were observed in sublamina b
of the IPL. In addition, a few synaptic contacts between
labeled cell processes were observed. Our results suggest
that NOS immunoreactive cells may be modulated by other
amacrine cells and ON cone bipolar cells, and act preferentially
on other amacrine cells.
New role for the primate fovea: A retinal excavation determines
photoreceptor deployment and shape
Authors: SPRINGER ALAN D.
Published: July 2002

In humans, an increasing density of foveal cone
photoreceptors occurs slowly over several years after birth,
and accounts for a region that subserves high visual acuity.
Concurrently, inner retinal cells move centrifugally away
from the foveal center. Such developmental rearrangements
reflect complex cellular remodeling after the retinal neuronal
cells have differentiated and have formed synapses. Explaining
foveal morphogenesis is difficult, because differentiated
neuronal cells seem incapable of moving actively. Presented
here is a biomechanical explanation of how the above events
occur. This hypothesis assumes that the cellular movements
throughout the retinal layers occur passively as the eye
grows and the retina is stretched. Retinal stretch was
simulated using virtual engineering models that were analyzed
with finite element analysis. A pit combined with retinal
stretch causes the retinal layers to deform in a way that
accounts for both the centrifugal and centripetal movement
of various retinal cell types. Axially directed, tensile
forces associated with stretching the retinal tissue surrounding
the pit also accounts for the elongated morphology of foveal
cone photoreceptors. These simulations suggest that a pit
is required for both the centripetal displacement of cone
cells toward the center of the fovea, and for the elongated
foveal cone morphology. Since the primate fovea may have
minimal impact on acuity, its primary role may be to initiate
foveal morphogenesis in slowly developing eyes.
Receptive field and orientation scatter studied by tetrode
recordings in cat area 17
Authors: HETHERINGTON P.A. , SWINDALE N.V.
Published: July 2002

The receptive-field positions and orientation preferences
of neurons occupying the same tangential location in visual
cortex are thought to be similar but to have an associated
random scatter. However, previous estimates of this scatter
may have been inflated by the use of subjective plotting
methods, sequential recording of single units, and residual
eye movements. Here we report measurements of receptive-field
position and orientation scatter in cat area 17 made with
tetrodes, which were able to simultaneously isolate and
record up to 11 nearby neurons (ensembles). We studied
355 units at 72 sites with moving light and dark bars.
Receptive-field sizes and positions were estimated by least-squares
fitting of Gaussians to response profiles. We found that
receptive-field position scatter was about half of the
ensemble average receptive-field size. We confirmed previous
estimates of orientation scatter, but calculations suggested
that much of it may be accounted for by anatomical scatter
in the positions of recorded neurons relative to the tetrode
in a smooth map. Orientation tuning width was positively
correlated with the degree of orientation scatter. Scatter
was not independent in the two eyes: deviations from the
local mean for both preferred orientation and receptive-field
position were correlated although a significant amount
of residual inter-ocular orientation and receptive-field
position scatter was present. We conclude that cortical
maps of orientation and receptive-field position are more
ordered than was previously thought, and that random scatter
in receptive-field positions makes a relatively small contribution
to cortical point image size.