Download Loss of Neurons in Magnocellular and Parvocellular Layers of the

LABORATORY SCIENCES
Loss of Neurons in Magnocellular and
Parvocellular Layers of the Lateral Geniculate
Nucleus in Glaucoma
Yeni H. Yücel, MD, PhD; Qiang Zhang, PhD; Neeru Gupta, MD, PhD;
Paul L. Kaufman, MD; Robert N. Weinreb, MD
Objective: To determine whether there is loss of lateral geniculate nucleus relay neurons, which convey visual information to the visual cortex, in experimental
glaucoma in monkeys.
Methods: Four cynomolgus monkeys with experimentally induced glaucoma in the right eye (referred to as
the glaucoma group) and 5 control monkeys were studied. In both groups, the same conditions of fixation, tissue processing, staining, and measurement were used.
In each monkey, the left lateral geniculate nucleus target neurons in magnocellular layer 1 and parvocellular
layers 4 and 6, connected to the right glaucomatous eye,
were studied. Immunocytochemistry with antibody to parvalbumin was used to specifically label relay neurons connecting to the visual cortex. The number of parvalbuminimmunoreactive neurons was estimated using an unbiased
3-dimensional counting method. The t test was used to
compare the experimental and control groups.
Results: The mean (±SD) number of neurons in mag-
From the Departments of
Ophthalmology (Drs Yücel,
Zhang, and Gupta) and
Laboratory Medicine and
Pathobiology (Dr Yücel),
University of Toronto, and the
Department of Ophthalmology
and the Health Sciences
Research Center, St Michael’s
Hospital (Drs Yücel, Zhang,
and Gupta), Toronto, Ontario;
the Department of
Ophthalmology and Visual
Sciences, University of
Wisconsin, Madison
(Dr Kaufman); and the
Glaucoma Center and the
Department of Ophthalmology,
University of California, San
Diego (Dr Weinreb).
F
nocellular layer 1 was significantly decreased in the glaucoma group compared with the control group
(20 692 ± 9567 vs 37 687 ± 8017; P = .02). The mean
(±SD) number of neurons in parvocellular layers 4 and
6 was significantly decreased in the glaucoma group compared with the control group (100 141 ± 44 906 vs
174 090 ± 39 136; P = .03). Data are given as the
mean ± SD.
Conclusion: Significant loss of lateral geniculate nucleus
relay neurons terminating in the primary visual cortex
occurs in the magnocellular and parvocellular layers in
an experimental monkey model of glaucoma.
Clinical Relevance: Knowledge of the fate of neurons
in the central visual system may lead to a better understanding of the nature and progression of visual loss in
glaucomatous optic neuropathy.
Arch Ophthalmol. 2000;118:378-384
OLLOWING the loss of afferent fibers in the central nervous system, target neurons
are known first to become
atrophic and then die by the
process of transneuronal degeneration.1-3 In
neurodegenerative diseases and brain
trauma, the primary injury triggers transneuronal degeneration; this causes extension of the disease process to neurons relatively spared during the primary injury.4-6
Little information exists regarding neuronal changes in target central visual neurons following the loss of afferent optic nerve
fibers in glaucoma.
Ninety percent of optic nerve fibers
that arise from retinal ganglion cells terminate in the lateral geniculate nucleus
(LGN).7-10 Recently, studies11 of the primate LGN provide evidence for motion
and color pathways organized into at least
3 distinct LGN neuronal populations oc-
ARCH OPHTHALMOL / VOL 118, MAR 2000
378
cupying separate layers. Neurons in the
magnocellular layers convey broadband,
luminance contrast, and motion signals;
neurons in parvocellular layers convey
green-red color opponent signals; and koniocellular neurons located between layers convey blue-on-yellow signals.11 Understanding neuronal changes in the LGN
may provide insights into affected pathways causing vision loss in glaucoma.
There are 2 populations of neurons
in the LGN, namely, interneurons and relay neurons. While the projections of LGN
relay neurons terminate in the primary visual cortex, the projections of interneurons are confined to the LGN.12 Parvalbumin, a calcium-binding protein, selectively
identifies the population of LGN neurons terminating in the primary visual
cortex.13,14
This study determines whether loss of
parvalbumin-immunoreactive LGN relay
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SUBJECTS AND METHODS
SUBJECTS
All studies were performed following the guidelines of the
Association for Research in Vision and Ophthalmology Resolution on the Use of Animals in Research. Four young adult
cynomolgus monkeys (Macaca fascicularis) with experimental glaucoma induced in the right eye by argon laser
scarification of the trabecular meshwork (referred to as the
glaucoma group)15 and 5 normal control cynomolgus monkeys were studied. The survival time after laser treatment
was 14 months.
In monkeys with experimental glaucoma, intraocular pressure (IOP) measurements were performed with a
pneumatonometer (Digilab, Norwell, Mass) under light sedation (intramuscular injection of ketamine hydrochloride, 5 mg/kg) and topical anesthesia (5% proparacaine
hydrochloride). The IOP was measured in each eye of each
monkey 3 times before laser treatment and 20 times during a 14-month period after laser treatment. The interval
between IOP measurements ranged from 5 to 39 days (mean,
26 days). The mean, median, minimum, and maximum IOPs
of control and glaucomatous eyes have been previously described (rows 1, 4, 5, and 6, Tables 1 and 2).16 In control
monkeys, the baseline IOP was within 12 to 19 mm Hg.
Based on previously reported optic nerve fiber counts
of the monkeys with experimental glaucoma (rows 1, 4, 5
and 6, Tables 3 and 4),16 and using previously described
morphometric techniques,17 we examined the brains of 4
monkeys in which optic nerve fiber loss when compared
with the fellow eye was 17%, 29%, 61%, and 100% (Table 1
and Table 2).
TISSUE PROCESSING
Under deep general anesthesia, animals were perfused through
the heart with 4% paraformaldehyde and 0.1% glutaraldehyde in phosphate buffer (pH 7.4), 0.1 mol/L. Control animals were anesthetized with an intramuscular injection of ketamine hydrochloride, 10 mg/kg, followed by an intramuscular
injection of pentobarbital sodium, 35 mg/kg, at the University of Wisconsin, Madison. The animals with experimental
glaucoma were anesthetized with an intramuscular injection of ketamine hydrochloride, 10 mg/kg, and acepromazine maleate, 0.5 mg/kg, followed by an intravenous injection of ketamine hydrochloride, 100 mg. After removal from
the skull, brains were fixed by immersion in 4% paraformaldehyde in phosphate buffer (pH 7.4), 0.1 mol/L, for at
neurons conveying visual information to the visual cortex
occurs in glaucoma.
RESULTS
LIGHT MICROSCOPY
At low power, the overall appearance of LGNs with glaucoma (Figure 1, right) appeared atrophic compared with
the control LGNs (Figure 1, left). Immunoreactivity in
layers 4 and 6 was less in glaucomatous (Figure 1, right)
compared with control (Figure 1, left) LGNs. ImmunoARCH OPHTHALMOL / VOL 118, MAR 2000
379
least 48 hours. The left LGNs were blocked in the coronal
plane and cryoprotected by immersion in 10% glycerin and
2% dimethyl sulfoxide in phosphate buffer, 0.1 mol/L, for 2
days and in 20% glycerin and 2% dimethyl sulfoxide in phosphate buffer, 0.1 mol/L, for 5 days. The blocks were frozen
in isopentane cooled by a mixture of 100% alcohol and dry
ice. Coronal sections (50 µm) of the entire LGN were cut serially on a sliding microtome. Every seventh section was
mounted onto a glass slide and stained with cresyl violet. Care
was taken to use the same tissue processing procedures for
all monkey brains. The remaining sections were stored in 25%
glycerin and 30% ethylene glycol in sodium phosphate, 0.05
mol/L, and stored at −20°C.18
IMMUNOCYTOCHEMISTRY
The primary antibody was a monoclonal antibody against
parvalbumin (clones PA-235; Sigma-Aldrich Corp, St Louis,
Mo). Parvalbumin, a calcium-binding protein, labels relay
neurons in the LGN layers that project axons to the visual
cortex.13,14 Sections were washed with Tris-buffered saline, 0.1 mol/L, and incubated with 0.2% octylphenoxypolyethoxyethanol (Triton-X; Sigma-Aldrich Corp) in Trisbuffered saline, 0.1 mol/L, for 15 minutes, followed by 3%
normal goat serum for 1 hour. Sections were incubated in
1:1000 diluted antibody in phosphate-buffered saline with
3% normal goat serum overnight at 4°C. After thorough
washing in repeated changes of phosphate-buffered saline
and Tris-buffered saline, they were reacted with secondary immunoglobulins using avidin-biotin-peroxidase. A supersensitive detection system kit (Biogenex, San Ramon,
Calif ) and peroxidase were used to localize the antigen by
incubation in 0.02% 3,3-diaminobenzidine and hydrogen
peroxide. Sections were mounted onto slides coated with
silane-based reagent (Vectabound; Vector, Burlingame,
Calif ), dehydrated, cleared, and cover-slipped. A negative
control was obtained by omitting the primary antibody.
COUNTING METHODS
Morphometry was performed using bright-field microscopy
with a color video camera (JVC, Yokohama, Japan), video and
computer monitors, and a computer. Stereological procedures that provide unbiased estimates of cell numbers were
used.19-22 Neurozoom software (Human Brain Project, La Jolla
Calif) enabled digital superposition of the sampling grids on
the tissue. Neuronal density and layer surface area measurements were performed on immunostained and cresyl
Continued on next page
reactivity in layers 1, 2, 3, and 5 showed no apparent difference between glaucomatous and control LGNs (Figure 1, left and right).
At high power, immunoreactivity was seen in the
cell body and in neuronal processes. In glaucomatous
LGNs, the cell bodies of neurons appeared smaller and
fewer in layers 4 and 6 (Figure 2, bottom). In addition, fewer neuronal processes were present between
neurons compared with the control (Figure 2, top). In
layer 1, although no difference in neuronal density was
apparent, the size of the cell bodies appeared to be
reduced.
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stained sections, respectively. The 6 layers of the LGN were
easily identified on stained sections. The layers were identified as layer 1 to layer 6 from ventral to dorsal. Ventral
layers 1 and 2 are magnocellular layers, while the remaining dorsal layers 3 through 6 are parvocellular layers. Layers 1, 4, and 6 of the left LGN are connected to the glaucomatous right eye, while layers 2, 3, and 5 are connected
to the nonglaucomatous left eye. To determine whether neurons are lost in magnocellular and/or parvocellular LGN
layers connected to a glaucomatous eye, neurons in the left
LGN layers 1, 4, and 6 were counted, and the counts were
compared with those from the left LGN layers 1, 4, and 6
in control monkeys. Retinal ganglion cells of the right nasal hemiretina and fovea project to the left LGN layers 1,
4, and 6, and compose approximately 50% of the right eye
retinal ganglion cells.9 The difference in nerve fiber loss between the nasal and temporal quadrants of the right optic
nerves was not statistically significant (P..05) for the monkeys examined in this study; therefore, changes observed
in left LGN layers 1, 4, and 6 are most representative for
changes observed in target LGN neurons. Left LGN layers
1, 4, and 6 of monkeys with a normal visual system were
used as controls rather than right LGN layers 1, 4, and 6
of the laser-treated monkeys, since significant decrease in
cell size has been observed in the undeprived layers in some
monocular experimental conditions.23 In addition, our preliminary results show that the neuronal number in the left
LGN layers connected to the control fellow eye in lasertreated monkeys appears to be reduced compared with the
neuronal number in the left LGN in control monkeys (unpublished data, 1999). Analysis was performed for magnocellular layer 1 and parvocellular layers 4 and 6, the latter sharing the same morphologic and functional properties.
LAYER VOLUME
Measurements of the surface area for each layer were made
on equally spaced sections (interval, 350 µm) containing
all 6 layers of the LGN, starting with a section selected randomly. Areas between the LGN layers were excluded. Lateral geniculate nucleus layers at low power (32.5 objective) and a point counting grid generated by the software
were visualized on the computer monitor. Using the mouse,
the operator marked the points located on a layer. Each point
corresponded to an area of 0.01 mm2 for the grid used for
layer 1, and 0.0225 mm2 for the grid used for layers 4 and
6. Layer surface area was calculated for each section by the
software by multiplying the number of points on the layer
with the area corresponding to a grid point. Layer surface
area for each section was multiplied by the interval (350
µm) between sections and summed by the software to calculate layer volume.
NEURON DENSITY
Neuron density measurements were made on 3 parvalbumin-immunostained sections taken from the anterior,
middle, and posterior LGN with all 6 layers at high power
using an oil immersion objective (3100, numerical aperture = 1.32), a bright-field microscope, and a color video
camera. Immunostained neurons were visualized on the
computer and video monitors. Cell counts were made at
tissue locations determined by a random and systematic sampling procedure using a superimposed grid method.24 Only
sample locations within the LGN layers were used for neuron density measurements. The size of the sampling grid
was adjusted for each layer so that there were at least 80
samples for that layer through the nucleus. To measure neuronal density, the optical dissector method was used. A 3-dimensional optical dissector composed of x-, y-, and z-axes
that were 50 3 50 3 10 µm, respectively, was placed within
the tissue section with a guard area above and below the
optical dissector. The neurons in focus intersecting the top
surface of the dissector were not counted. Only the first
encountered profile of the new cell bodies that came into
focus within the optical dissector and intersecting its right,
back, and bottom surfaces was counted.25,26 The excursion along the focusing axis (10 µm) and the thickness of
the section were measured with a microcator (model MT12;
Heidenhain, Traunreut, Germany) mounted on the microscope stage. Neuronal density per layer was estimated by
calculating the average neuronal density for at least 80 optical dissectors. The average neuronal density was adjusted for tissue shrinkage occurring during the tissue processing.
NUMBER OF NEURONS
The number of neurons in each layer was calculated by
multiplying the average density of neurons (neurons per
cubic millimeter) by layer volume.
STATISTICAL ANALYSIS
The t test was used to compare layer volume, neuronal density, and number of neurons in the LGN of glaucomatous
vs control monkeys. Data are given as mean ± SD unless
otherwise indicated.
STEREOLOGICAL MORPHOMETRY
Layer Volume
Morphometric studies were performed in left LGN magnocellular layer 1 and parvocellular layers 4 and 6 connected
to the right optic nerve in monkeys with experimental glaucoma in the right eye (n = 4) and in control monkeys (n = 5).
The volume of layer 1 ranged from 0.70 to 2.50 mm3 in
the glaucoma group, and from 2.00 to 3.04 mm3 in the
control group. The mean ± SD volume of layer 1 was significantly decreased in the glaucoma group compared with
the control group (P = .04).
MAGNOCELLULAR LAYER 1
Neuronal Density
Table 1 summarizes the volume, neuronal density, and
number of neurons for magnocellular layer 1 in the control and glaucoma groups.
ARCH OPHTHALMOL / VOL 118, MAR 2000
380
Neuronal density in layer 1 ranged from 11 848 to 17 041
neurons per cubic millimeter in the glaucoma group, and
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Table 1. Left Lateral Geniculate Nucleus Magnocellular
Layer 1 Features in the Control and Glaucoma Groups
Table 2. Left Lateral Geniculate Nucleus Parvocellular
Layers 4 and 6 Features in the Control
and Glaucoma Groups
Layer 1
Group*
Volume, mm3
Control
S1
2.85
S2
2.32
S6
3.04
S7
2.00
S10
2.63
Mean ± SD 2.57 ± 0.42
Glaucoma†
92 (100)
0.89
91 (61)
0.70
96 (29)
2.50
106 (17)
1.91
Mean ± SD 1.50 ± 0.85
Density,
Neurons/mm3
Layers 4 and 6
No. of ParvalbuminImmunoreactive
Neurons
Group*
14 589
14 066
15 466
13 339
15 455
14 583 ± 916
41 623
32 690
46 941
26 611
40 569
37 687 ± 8017
16 716
17 041
13 320
11 848
14 731 ± 2555
14 861
11 929
33 339
22 641
20 692 ± 9567
*Identification numbers in each group are arbitrary.
†Data in parentheses are the percentage of the optic nerve fiber loss.
Volume, mm3
Control
S1
12.84
S2
10.47
S6
8.88
S7
7.45
S10
10.47
Mean ± SD 10.02 ± 2.02
Glaucoma†
92 (100)
3.36
91 (61)
3.43
96 (29)
6.52
106 (17)
8.06
Mean ± SD 5.34 ± 2.34
Density,
Neurons/mm3
No. of ParvalbuminImmunoreactive
Neurons
17 915
18 857
18 105
16 669
15 701
17 449 ± 1254
227 005
197 271
158 109
124 971
163 095
174 090 ± 39 136
16 608
18 379
17 155
18 426
17 642 ± 906
56 439
69 346
122 959
151 822
100 141 ± 44 906
*Identification numbers in each group are arbitrary.
†Data in parentheses are the percentage of the optic nerve fiber loss.
6
6
5
5
4
4
3
3
2
2
1
1
Figure 1. Low-power microphotographs of coronal sections of the left lateral geniculate nucleus (LGN) from control (left) and glaucomatous (right) monkeys,
immunostained for parvalbumin. All 6 layers in the control are strongly immunoreactive for parvalbumin as indicated by numbers. There is overall shrinkage of the
LGN and a decrease in immunoreactivity in parvocellular layers 4 and 6 in the glaucomatous LGN compared with the control. The bar indicates 0.5 mm.
from 13 339 to 15 466 neurons per cubic millimeter in
the control group. The mean density of neurons in layer
1 did not differ significantly between the glaucoma and
the control groups (P..05).
ARCH OPHTHALMOL / VOL 118, MAR 2000
381
Number of Neurons
The number of neurons in magnocellular layer 1 ranged
from 11 929 to 33 339 in the glaucoma group, and from
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60
No. of Neurons, ×103
Glaucoma Group
50
Control Group
40
∗
30
20
10
0
Magnocellular Layer 1
45
No. of Neurons, ×103
40
35
30
25
20
15
10
5
0
25
50
75
100
Optic Nerve Fiber Loss, %
Figure 2. High-power microphotographs of lateral geniculate nucleus (LGN)
coronal sections show parvalbumin-immunoreactive neurons in layer 6 of
control (top) and glaucomatous (bottom) monkeys. In the controls, the
darkly stained cell bodies are plump and numerous; in the glaucomatous
monkeys, they are shrunken and few. The bar indicates 50 µm.
26 611 to 46 941 in the control group. The mean
number of neurons in magnocellular layer 1 was significantly decreased in the glaucoma group compared
with the control group (P = .02) (Figure 3, top). The
number of neurons in magnocellular layer 1 in the
glaucomatous monkeys showed a tendency to decrease
with increasing optic nerve fiber loss (Figure 3,
bottom).
PARVOCELLULAR LAYERS 4 AND 6
Table 2 summarizes the volume, neuronal density, and
number of neurons for parvocellular layers 4 and 6 in
the control and glaucoma groups.
Figure 3. Top, Mean number of parvalbumin-immunoreactive neurons in left
lateral geniculate nucleus (LGN) magnocellular layer 1 connected to the right
eye of control or glaucomatous monkeys. Error bars indicate SDs. The
asterisk indicates that the mean number of neurons was significantly
reduced by 45% in glaucomatous monkeys ( P = .02). Bottom, The number
of parvalbumin-immunoreactive neurons in the left LGN magnocellular layer
1 for the 4 glaucomatous monkeys with varying percentage of optic nerve
fiber loss. The horizontal solid line indicates the mean number of
parvalbumin-immunoreactive neurons in the left LGN magnocellular layer 1
for the control monkeys (n = 5). The horizontal dotted line indicates the
mean number of neurons minus 2 SDs for control monkeys.
rons in layers 4 and 6 did not differ significantly between the glaucoma and the control groups (P..05).
Number of Neurons
The number of neurons in parvocellular layers 4 and 6
ranged from 56 439 to 151 822 in the glaucoma group,
and from 124 971 to 227 005 in the control group. The
mean number of neurons in parvocellular layers 4 and 6
was significantly decreased in the glaucoma group compared with the control group (P = .03) (Figure 4, top).
The number of neurons in parvocellular layers 4 and 6
in the glaucomatous monkeys showed a tendency to decrease with increasing optic nerve fiber loss (Figure 4,
bottom).
COMMENT
Layer Volume
The combined volume of layers 4 and 6 ranged from 3.36
to 8.06 mm3 in the glaucoma group, and from 7.45 to
12.84 mm3 in the control group. The mean volume of
layers 4 and 6 was significantly decreased in the glaucoma group compared with the control group (P = .02).
Neuronal Density
Neuronal density in layers 4 and 6 ranged from 16 608
to 18 426 neurons per cubic millimeter in the glaucoma
group, and from 15 701 to 18 857 neurons per cubic millimeter in the control group. The mean density of neuARCH OPHTHALMOL / VOL 118, MAR 2000
382
Previous studies22,27,28 in monkey LGN have used the Nissl
stain, which labels all neurons, including relay neurons
and interneurons. In the present study, parvalbumin was
used to label only relay neurons connecting to the visual
cortex in the magnocellular and parvocellular layers.13,14 Neuron density measurements for the magnocellular and parvocellular layers were similar to measurements computed by Ahmad and Spear, 22 and
comparable coefficients of error for neuron number (9.5%
for layer 1 and 10% for layers 4 and 6) were obtained.
Since the stereological method used in this study has been
shown to be unbiased by the size, orientation, or shape
of the objects counted,24,26 neuronal density measureWWW.ARCHOPHTHALMOL.COM
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ARCH OPHTHALMOL / VOL 118, MAR 2000
383
No. of Neurons, ×103
220
200
180
160
140
120
100
80
60
40
20
0
Glaucoma Group
Control Group
∗
Parvocellular Layers 4 and 6
180
160
No. of Neurons, ×103
ments are not biased by a possible reduction in size of
neurons in magnocellular and parvocellular layers in
glaucoma (qualitative observation and preliminary
measurements).
Our study demonstrated neuronal loss in the magnocellular and parvocellular layers in experimental
glaucoma. These results are in keeping with a descriptive study29 showing weaker immunoreactivity for synaptophysin and neurofilament in magnocellular and
parvocellular layers, and with electrophysiologic studies30 reporting deficits in visually responsive cells in
magnocellular and parvocellular layers in experimental
glaucoma.
A previous study31 of human LGNs reported a preferential reduction of 2-dimensional estimates of neuron
density in the LGN magnocellular layer in glaucoma. In
our study, using 3-dimensional techniques, we found no
significant decrease in neuronal density in the magnocellular and parvocellular layers. The differences in our
findings might be explained by differences between human clinical and monkey experimental conditions, extent and/or duration of disease, and differences in method.
Histomorphometric studies32,33 in human clinical and
monkey experimental glaucoma, including measurements of cell body size and of axon diameter of the surviving retinal ganglion cells, suggest preferential loss of
large retinal ganglion cells. In addition, large retinal ganglion cells immunoreactive for neurofilament have been
shown to be preferentially lost in experimental glaucoma.34 The researchers32,33 suggest that retinal ganglion cells projecting to the magnocellular layers (M) are
preferentially lost in early glaucoma, based on the observation that M retinal ganglion cell bodies and axons
are relatively larger compared with cell bodies and axons
of retinal ganglion cells in normal retina projecting to the
parvocellular layers (P). The identification of retinal ganglion cell types on size alone may not be reliable35 for several reasons: overlap in cell body size between M and P
retinal ganglion cells occurs in normal monkey and human retina; S cells, a third class of retinal ganglion cells
involved in the blue on-center system, are similar in size
to M cells; and atrophic changes in glaucoma include a
reduction in cell body size and axon diameter of retinal
ganglion cells.36 In our study, the number of neurons in
the magnocellular and parvocellular layers showed a tendency to decrease with increasing optic nerve fiber loss.
Further studies of the LGN with a larger sample size and
with optic nerve fiber loss ranging from 30% to 60% may
provide evidence for preferential loss in these pathways.
Support for neuronal damage in magnocellular and
parvocellular pathways in glaucoma comes from various functional tests. Motion-automated perimetry, highfrequency temporal flicker perimetry, and frequencydoubling perimetry reveal deficits in the magnocellular
pathway in glaucoma.37-43 The parvocellular pathways are
known to convey red-green color information.44,45 Color
pattern–electroretinogram, sweep visual-evoked potentials, and psychophysical tests for red-green sensitivity
show deficits in the parvocellular pathway in glaucoma.46-49 There is evidence to suggest that the bluesensitive pathway is conveyed through a third informa-
140
120
100
80
60
40
20
0
25
50
75
100
Optic Nerve Fiber Loss, %
Figure 4. Top, Mean number of parvalbumin-immunoreactive neurons in left
lateral geniculate nucleus (LGN) parvocellular layers 4 and 6 connected to
the right eye of control or glaucomatous monkeys. Error bars indicate SDs.
The asterisk indicates that the mean number of neurons was significantly
reduced by 42% in glaucomatous monkeys ( P = .03). Bottom, The number
of parvalbumin-immunoreactive neurons in the left LGN parvocellular layers
4 and 6 for the 4 glaucomatous monkeys with varying percentage of optic
nerve fiber loss. The horizontal solid line indicates the mean number of
parvalbumin-immunoreactive neurons in the left LGN parvocellular layers 4
and 6 for the control monkeys (n = 5). The horizontal dotted line indicates
the mean number of neurons minus 2 SDs for the control monkeys.
tion channel located in the interlaminar zones of the
LGN,50,51 not examined in the present study. Shortwave automated perimetry testing blue-yellow sensitivity also reveals deficits in glaucoma.52-54
The significant loss of LGN relay neurons known
to send their axons to the primary visual cortex13,14 suggests that in glaucoma, degenerative changes are also occurring in the primary visual cortex. The present study
suggests that, in addition to retinal ganglion cell loss, the
loss of target neurons in at least the LGN is part of the
pathological process responsible for vision loss in glaucoma. Further studies to elucidate the mechanisms of neuronal death in the LGN are needed.
Accepted for publication October 6, 1999.
This study was supported by the Smith Barney Inc Research Fund of the Glaucoma Foundation, New York, NY
(Dr Yücel); the Glaucoma Research Society of Canada,
Toronto, Ontario (Dr Yücel); the Foundation for Eye Research, Rancho Santa Fe, Calif (Dr Yücel); grant EY02698
from the National Eye Institute, Bethesda, Md (Dr Kaufman); Research to Prevent Blindness Inc, New York, NY (Dr
Kaufman); and the Joseph Drown Foundation, Los Angeles, Calif (Dr Weinreb).
We thank Terri Kozano, Bsc, and B’Ann Gabelt, MSc,
for their excellent technical assistance at early stages of the
study.
Reprints: Yeni H. Yücel, MD, PhD, Ophthalmic Pathology Laboratory, Department of Ophthalmology, University of Toronto, 1 Spadina Crescent, Suite 125, Toronto,
Ontario, Canada M5S 2J5 (e-mail: [email protected]).
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