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Populations of Rod and Cone Photoreceptors in the Hamster Retina

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We report on a quantitative analysis of cone and rod photoreceptors in hamster retina. Cone and rod photoreceptors were counted in retinal whole mounts using differential interference contrast (DIC) optics microscopy after staining of cone photoreceptors were stained with peroxidase-labeled peanut lectin. Middle-to-long-wave-sensitive-(M/L-), and shortwave-sensitive-(S-) cone opsins were visualized by observed using confocal microscope after immunocytochemical procedure. The average cone density was 9,307 , giving a total of cones of 293,060 cone cells per retina. The peak density of cone cells (12,857 ) was found 0.3 mm from the optic disk (OD) of the nasal retina. The average rod density was 300,082 , giving a total number of rods of 9,448,150 cells. The peak density of rod cells was found 0.3 mm from the OD of the dorsal retina. Of all photoreceptors studied, the total percentage of rods and cones were 96.99% and cones 3.01%, respectively. The mean ratio of rod and cone was 32.24 : 1. The cone photoreceptors of hamster contained both M/L- and S-cone opsins. The present results suggest that the hamster retina is strongly rod-dominated with some photopic property of vision.
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291
INTRODUCTION
Most vertebrate retina have scotopic and photopic visual
systems. The rod-dependent scotopic visual system mediates
vision in dim light, and the cone-dependent photopic visual
system mediates vision in bright light (Wikler & Rakic, 1990;
Rodieck, 1998). In many animals, cone photoreceptors are also
essential for color vision. Since the differences in the spatial
density and distribution of the photoreceptors within the retina
are the most fundamental determinants of visual processing
information, the basic organization of the photoreceptor mosaic
has been well characterized in several animals. For example,
Packer et al. (1990) and Wikler et al. (1990) identified the
photoreceptor topography in monkey retina. Curcio et al.
(1990) and Chandler et al. (1999) identified photoreceptor
한국현미경학회지 제39권제42009
Korean J. Microscopy 39(4), 291~299(2009)
Populations of Rod and Cone Photoreceptors
in the Hamster Retina
Song-Hee Yu*, Hyun-Jin Kim, Kyoung-Pil Lee, Eun-Shil Lee,
Jea-Young Lee and Chang-Jin Jeon
Department of Biology, College of Natural Sciences, and Brain Science and Engineering Institute,
Kyungpook National University, Daegu 702-701, Korea
(Received September 23, 2009; Accepted December 24, 2009)
햄스터 망막에서의 광수용체 분포
유성희*, 김현진, 이경필, 이은실, 이제영, 전창진
경북대학교 자연과학대학 생물학과, 생명과학및뇌과학연
ABSTRACT
We report on a quantitative analysis of cone and rod photoreceptors in hamster retina. Cone and rod photoreceptors
were counted in retinal whole mounts using differential interference contrast (DIC) optics microscopy after staining of
cone photoreceptors were stained with peroxidase-labeled peanut lectin. Middle-to-long-wave-sensitive-(M/L-), and short-
wave-sensitive-(S-) cone opsins were visualized by observed using confocal microscope after immunocytochemical proce-
dure. The average cone density was 9,307 cells/mm2, giving a total of cones of 293,060 cone cells per retina. The peak
density of cone cells (12,857cells/mm2) was found 0.3mm from the optic disk(OD) of the nasal retina. The average rod
density was 300,082cells/mm2, giving a total number of rods of 9,448,150 cells. The peak density of rod cells was found
0.3mm from the OD of the dorsal retina. Of all photoreceptors studied, the total percentage of rods and cones were 96.99%
and cones 3.01%, respectively. The mean ratio of rod and cone was 32.24: 1. The cone photoreceptors of hamster contained
both M/L-and S-cone opsins. The present results suggest that the hamster retina is strongly rod-dominated with some pho-
topic property of vision.
Keywords : Cones, Density, Photoreceptors, Retinal mosaic, Rods
This Research was supported by Kyungpook National University Research Fund, 2008.
* Correspondence should be addressed to
Prof. Chang-Jin Jeon, Neuroscience Laboratory, Department of Biology, College of Natural Sciences, Kyungpook National
University, 1370 Sankyuk-dong, Daegu 702-701, Korea. Ph.: (053) 950-5343, Fax: (053) 953-3066, E-mail: cjjeon@knu.ac.kr
topography in human and pig, respectively. The density of
cone and rod photoreceptors in ground squirrel and mouse has
been identified by Kryger et al. (1998) and our group (Jeon et
al., 1998) respectively. Recently, the cone and rod photorecep-
tor populations in the retina of the bat have also been reported
by our group(Kim et al., 2008).
Hamster has been used in a broad range of biomedical stu-
dies. It is, however, surprising that no study of the number and
density of both rods and cones in hamster retina has been car-
ried out. Thus, our goal was to investigate the population of
both rods and cones in hamster retina. As vision is an impor-
tant sense in most mammals, this goal will provide critical
requirements in understanding the cellular architecture of the
hamster retina and the quality of visual information processing
in the hamster retina.
MATERIALS AND METHODS
1. Animals and tissue preparation
Adult Syrian hamsters (Mesocricetus auratus) (20~30 g)
were used in this study. Animals were anesthetized with a mix-
ture of ketamine hydrochloride (30~40 mg/kg) and xylazine
(3~6 mg/kg). A local anesthetic, proparacaine hydrochloride
(100~200 μL), was applied to the cornea to suppress blink
reflexes. The eyes were enucleated after a reference point was
taken to label the superior pole, and were immediately im-
mersed in 4% paraformaldehyde in 0.1M phosphate buffer (PB,
pH 7.4). The anterior segments of the eyes were removed and
the retinas were isolated from the eyecup and post-fixed for 2
hr in 2.5% glutaraldehyde in 0.1M PB. After being rinsed 3×
10 min in 0.1 M PB, retina tissues were processed as whole
mounts. Retinal tissues were processed as whole mounts and
were cut vertically into 50μm thick sections using a vibratome.
The guidelines of the National Institute of Health regarding
the Care and Use of Laboratory Animals were followed in all
experimental procedures.
2. Total cone photoreceptor staining
The whole mount retinas were incubated in 50μg/mL pero-
xidase-labeled peanut lectin (PNA, Sigma, St. Louis, MO,
USA) in 0.25 M Tris buffer, for 16~18 hr (Bridges, 1981;
Blanks et al., 1984; Jeon et al., 1998). PNA is known as a
general marker for labeling cone cells. Labeled cells were
visualized using a diaminobenzidine (DAB) reagent kit(Kirke-
gaard & Perry, Gaithersburg, MD, USA) in 0.25M Tris buffer.
Retinas were then rinsed, mounted flat on Superfrost Plus sli-
des (Fisher, Pittsburgh, PA, USA), and coverslipped with
DMSO. After 12hr, DMSO was replaced with 100% glycerol.
3. Immunocytochemistry for cone opsins
A polyclonal antibody against middle-to-long-wave-sensi-
tive-(M/L-) opsin was obtained from Chemicon(Temecula,
CA, USA). A polyclonal antibody against short-wave-sensitive
-
(S-) opsin was obtained from Santa Cruz (Santa Cruz, CA,
USA). These two antibodies have been widely used to label
M/L-opsin and S-opsin respectively. The primary antiserum
was diluted by the ratio of 1 : 250(M/L-opsin and S-opsin).
Standard immunocytochemistrical methods have been descri-
bed in detail in our previous studies (Jeon & Jeon, 1998; Jeon
et al., 1998). For detection by immunofluorescence, the secon-
dary antibody was fluorescein (FITC) conjugated anti-rabbit
IgG(Vector Lab., Burlingames, CA, USA) for detecting the
anti-M/L-opsin and anti-S-opsin. Labeled sections were cover-
slipped with Vectashield mounting medium (Vector Lab.).
Images were obtained on a Bio-Rad MRC 1024 laser scanning
confocal microscope.
4. Quantitative analysis of cones and rods
Both labeled cones and unlabeled rods could be examined
and photographed on a Zeiss Axioplan microscope using high
power differential interference contrast (DIC) optics (Curcio
et al., 1987; Jeon et al., 1998). Cell density was expressed as
the number of PNA-labeled cells/mm2of retinal surface. In
three DAB-reacted whole mount retinas, PNA-labeled cone
cells were viewed on a computer monitor using a Zeiss Plan-
Apochromat 100×objective and a Zeiss AxioCam HRc digi-
tal camera at 300 μm intervals along the central dorsoventral
and nasotemporal axes. The sample areas for counting the cone
cells were 70×70μm2. A transparency sheet was placed on
the computer monitor, and labeled cells were circled with a
pen. The samples were taken only at well-labeled positions
across the retinas. In three DAB-reacted whole mount retinas,
unlabeled rod cells were viewed on a computer monitor using
the same objective and digital camera at 300μm intervals along
the central dorsoventral and nasotemporal axes. The sample
areas for counting the rod cells were 30×30 μm2. The total
number of cells was determined in each sample area and ex-
pressed as the number of cells/mm2. The cell density was mul-
tiplied by retinal area to determine the total number of cells.
292 Korean J. Microscopy Vol. 39, No. 4, 2009
Yu SH et al. : Photoreceptor in the Hamster Retina 293
RESULTS
Fig. 1 shows mosaic of cones and rods in peripheral region
of the hamster retina. PNA-labeled cones (outlined darkly,
arrowhead) as well as unlabeled rods(outlined lightly and more
or less polygonal in shape, arrow) could be observed in this
high power DIC picture.
In three DAB-reacted whole mount retinas, cone cells in the
photoreceptor cell layer were counted. The estimated total num
-
ber of cone cells varied from 290,226 to 295,076 cells among
the three sampled retinas in this study. Table 1 and Fig. 2 show
the results. There were 290,226 cells in retina #1L, 295,076
cells in retina #2L, and 293,878 cells in retina #3R; therefore,
the average number of cone cells/retina was 293,060±2,526
(mean±SD; n
==
3). The mean density of cone cells was 9,307
±184cells/mm2in the three retinas (Table 1). The distribution
of total cone cells is shown in Fig. 2 and Table 2. The two
graphs(Fig. 2a and 2b) show the numbers of cells encountered
along the nasotemporal(Fig. 2a) and dorsoventral (Fig. 2b) axes
intersecting the optic nerve head(OD). In the present study,
the lowest density of cone cells (4,694±577, mean±SD; n
==
3) was found 3.0 mm from the OD of the temporal retina; the
peak density (12,857±353, mean±SD; n
==
3) appeared 0.3
mm from the OD in the nasal retina. The density gradient from
the point of the highest density to the point of the lowest den-
Fig. 1. High magnification differen-
tial interference micrographs of cone
and rod photoreceptors in a whole
mount tissue in hamster retina. The
lighter cells are rod inner segments
and the darker cells are cone inner seg
-
ments by the diaminobenzidine reac-
tion product. Arrows indicate some
rod cells, and arrowheads indicate
some cone cells. Scale bar
==
10μm.
Table 1. The densities of photoreceptor in Syrian hamster
Retina Sampled Sampled Cone cells Total retinal Mean density Total cone cells
area(n) area (μm2)acounter area (mm2) (cells/mm2)
Retina 1L 40 196,000 1,807 31 9,219 290,226
Retina 2L 39 191,100 1,819 31 9,519 295,076
Retina 3R 40 196,000 1,800 32 9,184 293,878
Mean±SD 9,307±184 293,060±2,526
Retina Sampled Sampled Rod cells Total retinal Mean density Total rod cells
area(n) area (μm2)bcounter area (mm2) (cells/mm2)
Retina 1L 44 39,600 12,118 31 306,010 9,633,198
Retina 2L 42 37,800 11,503 31 304,312 9,433,677
Retina 3R 44 39,600 11,481 32 289,924 9,277,576
Mean±SD 300,082±8,838 9,448,150±178,252
L, left; R, right
aOne sampled area
==
70×70μm2; bOne sampled area
==
30×30μm2
sity was 2.74.
In three DAB-reacted whole mount retinas, rod cells in the
photoreceptor cell layer were also counted. The estimated total
number of rod cells varied from 9,277,576 to 9,633,198 cells
among the three sampled in this study. Table 1 and Fig. 2 show
the results. There were 9,633,198 cells in retina #1L, 9,433,677
cells in retina #2L, and 9,277,576cells in retina #3R; therefore,
the average number of rod cells/retina was 9,448,150±178,252
(mean±SD; n
==
3). The mean density of rod cells was 300,082
±8,838 cells/mm2in the three retinas (Table 1). The distribu-
tion of total rod cells is shown in Fig. 2 and Table 2. The two
graphs (Fig. 2c and 2d) show the numbers of cells encountered
along the nasotemporal (Fig. 2c) and dorsoventral (Fig. 2d)
axes intersecting the OD. The lowest density of rod cells
(248,148±24,478, mean±SD; n
==
3) was found 3.3 mm from
the OD of the nasal retina; and the peak density (340,000±
5,879, mean±SD; n
==
3) appeared 0.3mm from the OD in the
dorsal retina in this study. Thus, on average, rods are 96.99%
and cones are 3.01% of all the photoreceptors. The density of
rod cells has a slightly flatter distribution than that of cones.
294 Korean J. Microscopy Vol. 39, No. 4, 2009
Fig. 2. Spatial densities of cones(a, b) and rods (c, d) encountered along two axes, nasotemporal(a, c) and dorsoventral (b, d), intersecting the
optic nerve head.
160
120
80
40
0
Retina 1
Retina 2
Retina 3
400
300
200
100
0
400
300
200
100
0
-
2.7
-
2.1
-
1.5
-
0.9
-
0.3 0.3 0.9 1.5 2.1 2.7
Nasal eccentricity (mm) temporal
-
3.3
-
2.7
-
2.1
-
1.5
-
0.9
-
0.3 0.3 0.9 1.5 2.1 2.7 3.3
Nasal eccentricity (mm) temporal
-
3.3
-
2.7
-
2.1
-
1.5
-
0.9
-
0.3 0.3 0.9 1.5 2.1 2.7 3.3
Dosal eccentricity (mm) ventral
-
2.7
-
2.1
-
1.5
-
0.9
-
0.3 0.3 0.9 1.5 2.1 2.7
Dasal eccentricity (mm) ventral
(a) (b)
(c) (d)
160
120
80
40
0
Cone density (cells×102/mm2)Rod density (cells×102/mm2)
Cone density (cells×102/mm2)
Rod density (cells×102/mm2)
Yu SH et al. : Photoreceptor in the Hamster Retina 295
Table 2. Distribution of photoreceptor at different locations in three retinas of Syrian hamster
Retinal eccentricity
D9 D8 D7 D6 D5 D4 D3 D2 D1 V1 V2 V3 V4 V5 V6 V7 V8 V9 V10 V11
33 34 36 38 40 46 55 58 61 59 56 52 49 48 48 42 38 32 27
6,735 6,939 7,347 7,755 8,165 9,388 11,224 11,837 12,449 12,041 11,429 10,612 10,000 9,796 9,796 8,571 7,755 6,531 5,510
32 40 41 45 48 50 55 57 60 62 57 54 52 46 43 44 41 38 27
6,531 8,163 8,367 9,184 9,796 10,204 11,224 11,633 12,245 12,653 11,633 11,020 10,612 9,388 8,776 8,980 8,367 7,755 5,510
31 35 41 46 50 52 52 57 61 66 60 54 51 46 42 40 37 25 20
6,327 7,143 8,367 9,388 10,204 10,612 10,612 11,633 12,449 13,469 12,245 11,020 10,408 9,388 8,571 8,163 7,551 5,102 4,082
245 252 260 272 278 283 305 309 312 306 296 290 294 270 260 255 249 250 228 230
272,222 280,000 288,889 302,222 308,889 314,444 338,889 343,333 346,667 340,000 328,889 322,222 326,667 300,000 288,889 283,333 276,667 277,778 253,333 255,556
249 262 269 281 284 286 290 308 304 300 292 290 301 281 285 269 256 242 240
276,667 291,111 298,889 312,222 315,556 317,778 322,222 342,222 337,778 333,333 324,444 322,222 334,444 312,222 316,667 298,889 284,444 268,889 266,667
237 257 261 277 287 296 292 300 302 292 295 300 285 286 263 261 250 246 247 234
263,333 285,556 290,000 307,778 318,889 328,889 324,444 333,333 335,556 324,444 327,778 333,333 316,667 317,778 292,222 290,000 277,778 273,333 274,444 260,000
N9 N8 N7 N6 N5 N4 N3 N2 N1 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11
40 45 47 53 53 54 57 59 62 61 57 54 51 45 40 40 34 30 21
8,163 9,184 9,592 10,816 10,816 11,020 11,633 12,041 12,653 12,449 11,633 11,020 10,408 9,184 8,163 8,163 6,939 6,122 4,286
37 38 40 41 46 50 54 55 65 59 57 53 52 52 50 45 46 37
7,551 7,755 8,163 8,367 9,388 10,204 11,020 11,224 13,265 12,041 11,633 10,816 10,612 10,612 10,204 9,184 9,388 7,551
29 36 44 46 49 54 55 60 62 61 58 53 49 46 47 42 37 37 25
5,918 7,347 8,980 9,388 10,000 11,020 11,224 12,245 12,653 12,449 11,837 10,816 10,000 9,388 9,592 8,571 7,551 7,551 5,102
258 266 265 276 283 291 303 309 311 308 313 310 303 304 292 280 270 264 248 240
286,667 295,556 294,444 306,667 314,444 323,333 336,667 343,333 345,556 342,222 347,778 344,444 336,667 337,778 324,444 311,111 30,000 393,333 275,556 266,667
241 253 261 280 278 288 290 290 297 296 307 293 290 279 272 274 265 260 254
267,778 281,111 290,000 311,111 308,889 320,000 322,222 322,222 330,000 328,889 341,111 325,556 322,222 310,000 302,222 304,444 294,444 288,889 282,222
226 229 246 252 253 264 267 269 288 281 280 264 278 275 261 255 250 244 235 229
251,111 254,444 273,333 280,000 281,111 293,333 296,667 298,889 320,000 312,222 312,222 311,111 293,333 308,889 290,000 283,333 277,778 271,111 261,111 254,444
D, dorsal; V, ventral; N, nasal; T, temporal
D11 D10
Cone photoreceptors
Retina 1
Number of cells 24
Density(cells/mm
2
) 4,898
Retina 2
Number of cells 24
Density(cells/mm
2
) 4,898
Retina 3
Number of cells 22
Density(cells/mm
2
) 4,490
Rod Photoreceptor
Retina 1
Number of cells 233 240
Density(cells/mm
2
) 258,889 266,667
Retina 2
Number of cells 235 255
Density(cells/mm
2
) 261,111 283,333
Retina 3
Number of cells 223 233
Density(cells/mm
2
) 247,778 258,889
N11 N10
Cone photoreceptors
Retina 1
Number of cells 28
Density(cells/mm
2
) 5,714
Retina 2
Number of cells 26
Density(cells/mm
2
) 5,306
Retina 3
Number of cells 22
Density(cells/mm
2
) 4,490
Rod photoreceptors
Retina 1
Number of cells 246 261
Density(cells/mm
2
) 273,333 290,000
Retina 2
Number of cells 222 234
Density(cells/mm
2
) 246,667 260,000
Retina 3
Number of cells 202 209
Density(cells/mm
2
) 224,444 232,222
The density gradient of rod cells from the point of the highest
density to the point of the lowest density was 1.98. The density
of cone and rod cells in hamster(Jeon et al., 1998) is similar to
that of mouse in the present study.
The mean ratio of rod and cone in the hamster was 32.24 :
1. The ratios between rod and cone photoreceptors did not vary
significantly with changes in eccentricity(Table 3). The lowest
rod:cone ratio of 26.22±2.08 (mean±SD; n
==
3) : 1 was found
in the central retina, 0.3mm from the OD of the ventral retina.
However, the ratio did not significantly increase in the peri-
pheral retina. No areas showed three fold changes in the rod:
cone ratio. The highest rod : cone ratio of 57.74±9.27 (mean
±SD; n
==
3) :1 was found in the far peripheral retina, 3.0 mm
from the OD of the temporal retina.
In order to determine whether cones contain cone opsin, we
labeled retina tissues with antibody against cone opsin, protein
found in cone photoreceptors (Szél et al., 1996). Fig. 3 shows
50 μm vertical sections through a M/L-(Fig. 3a and 3b) and
S-(Fig. 3c and 3d) cone opsin-immunoreactive hamster retina
from a mid-pheripheral region. In the outer segment (arro-
wheads in Fig. 3b and 3d) of the outer nuclear layer, M/L-and
S-cone opsin were found in many photoreceptors of the ham-
ster retina.
DISCUSSION
As the knowledge about the spatial density and distribution
of the photoreceptor is an indispensable part studying of the
relationship between structure and function in retina, the num-
ber and distribution of cone and rod photoreceptors have been
extensively studied in various animals such as human(Curcio
et al., 1990), monkey (Packer et al., 1989; Wikler & Rakic,
1990; Wikler et al., 1990; Andrade et al., 2000), pig(Chandler
et al., 1999), opossum(Kolb & Wang, 1985), cat (Steinberg et
al., 1973; Hughes, 1975), rabbit(Hughes, 1971), rat (Hallett,
1987; Szél & Röhlich, 1992; Peichl, 2005), ground squirrel
(Kryger et al., 1998), gerbil(Govardovskii et al., 1992), mouse
(Jeon et al., 1998), salmonoid fish(Beaudet et al., 1997), mole
(Glösmann et al., 2008), and bat(Kim et al., 2008). The retina
is dominated by rod photoreceptors in most mammals. For
example, human(Curcio et al., 1990) and rhesus monkey (Wik-
ler et al., 1990) retinas contain approximately 95% of rod pho-
toreceptors of all the photoreceptors. In most mammals, the
range of rod density varies from almost 99% to approximately
85% (Govardovskii et al., 1992; Szél & Röhlich, 1992). How-
296 Korean J. Microscopy Vol. 39, No. 4, 2009
Table 3. Ratio of rod to cone densities encountered along two axes intersecting the optic nerve head of Syrian hamster
Retinal eccentricity
D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 V1 V2 V3 V4 V5 V6 V7 V8 V9 V10
Retina 1L 54.44 40.42 40.35 39.32 38.97 37.83 33.49 30.19 29.01 27.85 28.24 28.78 30.36 32.67 30.62 29.49 33.06 35.68 42.53 45.98
Retina 2L 57.85 42.36 35.66 35.72 34.00 32.21 31.14 28.71 29.42 27.58 26.34 27.89 29.24 31.52 33.26 36.08 33.28 34.00 34.67 48.40
Retina 3R 57.66 41.62 39.98 34.66 32.78 31.25 30.99 30.57 28.65 26.95 24.09 26.77 30.25 30.43 33.85 34.09 35.53 36.79 53.57 67.23
Mean 56.65 41.47 38.66 36.57 35.25 33.76 31.88 29.82 29.03 27.46 26.22 27.81 29.95 31.54 32.58 33.22 33.96 35.49 43.59 53.87
SD 1.91 0.98 2.61 2.44 3.28 3.55 1.40 0.99 0.38 0.46 2.08 1.01 0.62 1.12 1.72 3.38 1.36 1.41 9.49 11.64
Retinal eccentricity
N10 N9 N8 N7 N6 N5 N4 N3 N2 N1 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10
Retina 1L 30.70 28.35 29.07 29.34 28.94 28.51 27.31 27.49 29.90 31.26 32.35 36.78 39.75 38.11 4.32 50.75 35.12 32.18 64.25 64.29
Retina 2L 34.66 33.88 31.53 31.36 28.71 27.70 26.95 27.31 29.32 30.10 30.36 29.21 29.62 33.15 31.36 53.08 41.00 34.44 38.26
-
Retina 3R 30.44 29.83 28.11 26.62 26.43 24.41 25.29 25.08 26.38 28.76 29.33 32.90 30.23 33.06 36.79 51.72 42.43 34.63 35.90 51.18
Mean 31.93 30.68 29.57 29.11 28.03 26.87 26.52 26.63 28.53 30.04 30.68 32.96 33.20 34.77 24.16 51.85 39.52 33.75 46.14 57.74
SD 2.37 2.86 1.76 2.38 1.39 2.17 1.08 1.34 1.89 1.25 1.53 3.78 5.68 2.89 17.39 1.17 3.88 1.36 15.73 9.27
D, dorsal; V, ventral; N, nasal; T, temporal
Yu SH et al. : Photoreceptor in the Hamster Retina 297
ever, some mammalian retinas are dominated by cone photo-
receptors. The tree shrew contains approximately 95% of cone
photoreceptors of all the photoreceptors(Petry et al., 1993).
We have estimated the total number of rods and cones in
three whole mounted hamster retinas using DIC optics in con-
junction with peanut lectin labeling. In the present study, rods
were 96.99%, and cones were 3.01% of all the photoreceptors.
The population density of cone and rod cells in the present
study is very similar to that of mouse. In mouse retina from
our previous study(Jeon et al., 1998), we found that rods were
97.2%, and cones were 2.8% of all photoreceptors. Rat also
contained 1~10% of cone photoreceptors of all the photore-
ceptors (Hallett, 1987; Szél & Röhlich, 1992; Peichl, 2005).
Thus, the combined results indicate that the Rodentia rat,
mouse and hamster show similar topographic properties of
cone and rod photoreceptors. However, the Rodentia gerbil
contained slightly higher numbers of cones: 13~14% of cone
photoreceptor of all photoreceptors. By contrast, the Rodentia
ground squirrel contained up to 95% of cones of all photore-
ceptors(Szél & Röhlich, 1988). These results indicate that the
features and qualities of the visual processing are very different
among the order Rodentia. As the differential constituents of
cone and rod photoreceptors reflect diurnal and nocturnal
behavior, respectively (Wikler and Rakic, 1990; Umino et al.,
2008), the distribution of photoreceptor subtypes in the retina
of hamster indicates that this is a nocturnal animal. It is also
very interesting the population density of cone and rod cells
in hamster retina is very similar to that of the nocturnal bat. In
a Microchiroptera bat retina from our previous study (Kim et
al., 2008), we found that rods were 97.5%, and cones were
Fig. 3. Confocal micrographs of M/L-, S-opsin labeled cells in 50μm vertical sections of fluorescence-reacted hamster retina. (a) M/L-opsin la-
beled cells were found in the ONL. (b) Higher magnification of M/L-opsin labeled photoreceptors in the ONL. (c) S-opsin labled cells were found in
the ONL. (d) Higher magnification of S-opsin labeled photoreceptors in the ONL. Arrowheads in (b, d) indicate cone outer segment. M/L-opsin,
middle-to-long-wave-sensitive-opsin; S-opsin, short-wave-sensitive-opsin; ONL, outer nuclear layer; OPL, outer plexiform layer. Scale bar
==
20μm
(a, c), Scale bar
==
30μm (b, d).
ab
cd
2.5% of all photoreceptors.
In primate retina, both populations of photoreceptors have
an area of high peak density: the fovea for the cones, and an
area near the fovea for the rods. Thus, both cone and rod photo-
receptor populations have a marked center-to-periphery gradi-
ent in photoreceptor density (Petry et al., 1993). However,
hamster retina did not show a pronounced center-to-periphery
gradient in photoreceptor density. The density gradient was
2.74 for cones and 1.98 for rods in the hamster retina. As ex-
pected, this is because of the lack of the fovea in rodents. The
density gradient in hamster retina is slightly higher than that
of mouse (Jeon et al., 1998). The data suggest the quality of
visual acuity in central: peripheral areas in hamster retina is
slightly lower than that of mouse. The average cone density in
the hamster retina is similar found in the primate’s retina at 3~
4 mm eccentricity (Packer et al., 1989). However, at the same
eccentricity, the rod cell population is much higher in hamster
retina than in the primate retina. These results indicate that
one of the major differences in the photoreceptor mosaics bet-
ween primate and the hamster is the higher density of the rod
photoreceptors in the rodent.
In addition, the present study shows that hamster retina con-
tains M/L-, S-opsins in cone photoreceptors. Cone opsins are
related with color vision and can be further seperated into three
subgroups, which are in accord well with their absorption spec-
tra: L-opsins (red opsin), M-opsins (green opsin) and S-opsins
(blue opsin). Thus, the existence of significant numbers of cone
cells and the existence of M/L-and S-cone opsins in the pre-
sent study strongly reflect visual abilities such as scotopic or
color vision, resolution and detection acuity, spatial discri-
mination, and pattern recognition (Hirsch & Miller, 1987; Thi-
bos et al., 1987; Williams & Coletta, 1987).
In conclusion, the hamster retina contains well-organized
spatial density distribution and spatial density of cones and
rods. Hamsters are strongly rod-dominated animals. Since the
topographic property of these photoreceptors and the existence
of M/L-, S-opsins in the cone photoreceptors has been con-
sidered to be one of the diverse factors in determining the fea-
tures and quality of the vision, the present results should be
importantly applicable to a better understanding of the visual
processing in hamster visual system.
ACKNOWLEDGEMENTS
We thank Peter Durrant for proofreading the paper.
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국문초록¤
본 연구에서는 햄스터 망막의 추상과 간상 광수용체의 양적 분
석을 하였다. 추상 광수용체를 과산화 효소로 표지된 피넛 렉틴
(peroxidase-labeled peanut lectin)을 사용하여 염색한 뒤 광학 미분
간섭 현미경 (DIC, differential interference contrast optics)을 사용하
여 관찰하였다. 또한 면역세포화학적 방법으로 추상 광수용체에 위
치한 M/L-옵신과 S-옵신을 염색한 뒤 공초점 형광 현미경 (confo-
cal microscope)을 사용하여 관찰하였다. 추상세포의 평균 밀도는
9,307 cells/mm2이며 전체 추상세포는 293,060개였다. 추상세포의
최대값 (12,857 cells/mm2)은맹(시신경 유두, optic disk)로부터
코쪽망(nasal retina)으로 0.3mm 떨어진 곳에 위치하였다.
세포의 평균은 300,082 cells/mm
2
으로 전체 간상세포는
9,448,150
개였다. 간상세포의 최대값 (340,000 cells/mm2)은 맹점으로부터 등
쪽망(dorsal retina) 방향으로 0.3 mm 떨어진 곳에서 발견되었다.
평균적으로 전체 광수용체 중, 간상세포의 전체 분포는 96.99%
고 추상세포는 3.01%를 차지하였다. 또한 간상과 추상의 평균 비
32.24: 1이었다. 햄스터의 추상세포는 M/L-S-옵신을 가진다.
본 연구 결과는 햄스터가 일부 명소시를 가지는 강한 간상 우세 망
막임을 제시한다.
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