Ultrastructural Localization and Expression of TRPM1 in
the Human Retina
Jan Klooster,1Joyce Blokker,1Jacoline B. ten Brink,2Unga Unmehopa,3Kees Fluiter,4
Arthur A. B. Bergen,2and Maarten Kamermans1,4
PURPOSE. Transient receptor potential subfamily melastatin
(TRPM)1 cation channels of retinal ON-bipolar cells are mod-
ulated via a mGluR6 (GMR6) signaling cascade. While light-
microscopy shows these channels are located on the tips of
ON-bipolar cells dendrites, near rod and cone synaptic ribbons,
TRPM1 localization at the electron-microscope level is cur-
rently not described. The authors report here the ultrastruc-
tural localization of TRPM1 in the human retina.
METHODS. TRPM1 was localized in postmortem human retinas
by immunohistochemistry at both the light and electron mi-
croscope levels. Additionally, TRPM1 expression was studied
using in situ hybridization, laser dissection microscopy, and
RESULTS. TRPM1-immunoreactivity was located on the den-
drites and soma of ON-bipolar cells at the light microscope
level. At the electron microscope level TRPM1-immunoreac-
tivity was located on the tips of ON-bipolar cell dendrites
that were invaginating cone pedicles and rod spherules. In
addition, TRPM1-immunoreactivity was occasionally found
on the rod spherules ribbons, suggesting that at least a
proportion of rods may also express TRPM1. In situ hybrid-
ization showed TRPM1 encoding RNA in inner nuclear layer
somata and in some photoreceptors. The presence of
TRPM1-RNA in photoreceptors was confirmed by PCR in
pure photoreceptor material obtained with a laser dissection
CONCLUSIONS. In the human retina TRPM1 is expressed on
ON-bipolar cell dendrites that invaginate photoreceptor termi-
nals. TRPM1 is also expressed on the synaptic ribbons of a
subclass of rods, suggesting a dual function for TRPM1 in the
ON-pathway. (Invest Ophthalmol Vis Sci. 2011;52:8356–8362)
ceptor signals are split into ON- and OFF- channels at the
photoreceptor synapse. Photoreceptors stimulated by light hy-
he retina sends information about the visual environment
to the brain via a number of parallel pathways.1Photore-
perpolarize and reduce their glutamate release. The reduction
in glutamate causes OFF-bipolar cells to hyperpolarize and
ON-bipolar cells to depolarize. The OFF- and ON-bipolar cells
react differently to changes in glutamate levels as they ex-
press distinct types of glutamate receptors. OFF-bipolar cells
express ionotropic glutamate receptors,1which are cation
channels that open when stimulated by glutamate. ON-bipo-
lar cells express the metabotropic glutamate receptor
mGluR62,3that when activated by glutamate leads to the
closure of the cation channel: transient receptor potential
subfamily melastatin (TRPM)1.4,5
In both mice and human, the lack of TRPM1 impairs retinal
functioning at the bipolar cell level evidenced by reduced
electroretinogram (ERG) b-wave while the a-wave remains un-
disturbed.5–7A number of other proteins such as the G protein
Goand Nyctalopin (NYX) seems to be essential in the mGluR6/
TRPM1 cascade.2,3,8As for TRPM1, mutations in mGluR6 or
NYX7,9–11also led to a reduced ERG b-wave while leaving the
a-wave undisturbed, suggesting that these three proteins be-
long to the same functional cascade.8Membership to the same
functional cascade is further supported by previous work on
the ultrastructural localization of mGluR6 and NYX, which
indicates these proteins are localized close together on ON-
bipolar cell dendrites near photoreceptor synaptic ribbons.8As
yet, however, the ultrastructural localization of TRPM1 has not
Here we show the ultrastructural localization of TRPM1 in
the human retina. TRPM1-immunoreactivity (IR) was found on
dendrites of ON-bipolar cells invaginating the synaptic termi-
nals of rods and cones near the synaptic ribbon. This localiza-
tion puts TRPM1 at the same location as mGluR6 and NYX,
further strengthening the argument that they form a functional
cascade. Surprisingly, TRPM1-IR was also found on the synap-
tic ribbon of some rods. Both findings were confirmed by in
situ hybridization (ISH) and polymerase chain reaction (PCR).
These results suggest that TRPM1 has both a pre- and postsyn-
aptic function in the human retina.
This study was performed in agreement with the declaration of Hel-
sinki on the use of human material for research. Postmortem human
donor eyes were obtained from the Cornea Bank Amsterdam. In ac-
cordance with The Netherlands’ law, the Cornea Bank Amsterdam
ensured donors had consented to their eyes being used for scientific
Retinas were isolated by peeling away the sclera and corpus vitre-
ous and fixed in 4% paraformaldehyde buffered in 0.1 M phosphate
buffer (PB) pH 7.4 for 30 to 60 minutes. Retinas were cryoprotected in
12.5% sucrose in 0.1 M phosphate buffer for 30 minutes, then 1 hour
in 25% sucrose in 0.1 M phosphate buffer before being frozen in
embedding compound (TissueTek; Sakura Finetek Holland BC, Alphen
aan de Rijn, The Netherlands).
From the Departments of1Retinal Signal Processing,2Molecular
Amsterdam, The Netherlands; and4Department of Neurogenetics, Ac-
ademic Medical Centre, Amsterdam, The Netherlands.
Supported by European Commission FP7 Grant RETICIRC
HEALTH-F2-2009-223156 (coordinator, MK), and ZonMW-NWO (MK).
Submitted for publication March 17, 2011; revised July 26, 2011;
accepted August 9, 2011.
Disclosure: J. Klooster, None; J. Blokker, None; J.B. ten Brink,
None; U. Unmehopa, None; K. Fluiter, None; A.A.B. Bergen, None;
M. Kamermans, None
Corresponding author: Maarten Kamermans, Department of Reti-
nal Signal Processing, Netherlands Institute for Neuroscience, Meiberg-
dreef 47, 1105 BA Amsterdam, The Netherlands;
3Neuropsychiatric Disorders, NIN-KNAW,
Investigative Ophthalmology & Visual Science, October 2011, Vol. 52, No. 11
Copyright 2011 The Association for Research in Vision and Ophthalmology, Inc.
For light microscopical (LM) purposes 10-?m thick sections were
made and stored at ?20 °C. Sections were first preincubated in 2%
normal goat serum (NGS) for 30 minutes, then incubated with primary
antibodies for 24 to 48 hours followed by 35 minutes of incubation
with secondary antibodies at 37 °C. Optical examination (optical sec-
tion thickness is 0.25 ?m) was performed with a confocal laser scan-
ning microscope (CLSM; Meta confocal miscroscope; Zeiss, Stuttgart,
The primary antibodies used were: TRPM1 (Sigma Aldrich Chemi
BV, Zwijndrecht, The Netherlands) 1:200; calbindin (Swant, Marly,
Switzerland) 1:500; mGluR6 (gift of Noga Vardi) 1:5000; Go(Chemi-
con, Hampshire, United Kingdom) 1:5000; Ribeye (BD Transduction
Laboratories, Breda, The Netherlands) 1:1000; Bassoon (Stress Gen,
Brussels, Belgium) 1:5000; PKC?(Sigma Aldrich Chemi BV) 1:200;
and PKC?(Sigma Aldrich Chemi BV) 1:200; diluted in 0.1 M phos-
phate buffered saline (PBS) containing 5% normal goat serum and
0.05% Triton. Secondary antibodies were visualized by means of
goat anti-rabbit Cy3, 1:500, and goat anti-mouse Alexa 488, 1:500.
For electron microscopical (EM) purposes 40-?m thick sections
were incubated with TRPM1 (1:200) in phosphate buffer for 48
hours, then rinsed before being incubated with rabbit peroxidase
antiperoxidase (PAP) for 2 hours, rinsed, then developed in a
2,2?-diaminobenzidine (DAB) solution containing 0,03% H2O2for 4
minutes. Afterward the gold substitute silver peroxidase12method
was performed; sections were fixed in sodium cacodylate buffer
(pH 7.4) containing 1% osmium tetra oxide and 1.5% potassium
ferricyanide. Sections were then dehydrated and embedded in ep-
oxy resin, ultrathin sections made, and examined with an electron
microscope (FEI Technai 12; Fei Company, Eindhoven, The Neth-
For Western blot analysis, human retinas were homogenized
with a nonstick pestle in ice-cold phosphate buffered saline con-
taining one tablet of protease-inhibitor cocktail (Boehringer Mann-
heim GmbH, Mannheim, Ingelheim, Germany) per 25 mL. Proteins
fractions were isolated by centrifuge (14,600g), the supernatants
and deposits were collected, sample buffer (Nu Page LDS; Invitro-
gen, Breda, The Netherlands) was added and then run on a gel (Nu
Page 4–12% Bis Tris Cell; Invitrogen). Protein standards (Bio-rad
Laboratories, BV, Veenendaal, The Netherlands) were run in adja-
cent lanes. Gels were electroblotted on blot membrane (Poly-
VinylideneDiFluoride; Millipore, Amsterdam, The Netherlands)
overnight at 80 mA. Membranes were rinsed in a Tris buffer (0.5 M)
containing NaCl (1.5 M) and 5% Tween-20, blocked in the same
buffer containing 2% dry milk powder for 1 hour, then incubated in
the primary antibodies against TRPM1 for 1 hour, washed in Tris-
buffer, and incubated in goat anti-rabbit (IRDye 800 CW; 1:3000).
Blots were examined on an Odyssey infrared detecting system.
Western blot analysis showed a strong band between 150 kDa and
200 kDa (Fig 1). The predicted molecular weight of TRPM1 is 182
kDa, suggesting that the band between 150 kDa and 200 kDa
represents TRPM1. Two additional bands were seen; a strong band
between 100 kDa and 150 kDa and a weaker band between 75 kDa
and 100 kDa, which are most likely degradation products or alter-
native splicing variations of TRPM1.
For in situ hybridization (ISH) sections were stored at ?80 °C.
Hybridization was performed using TRPM1 specific, 5?-fluorescein-
labeled 19mer antisense oligonucleotides containing locked nucleic
acid (LNA) and 2?-O-methyl (2OME)-RNA moieties; TRPM1 (5?-TuuC-
ccAaaGacTugTuuC-3?) and mGluR6 (5?-TguTccTgcGguTguTcuC- 3?),
where locked nucleic acid residues are given in capital letters and
2?-O-methyl in lowercase. Sense probes were used as controls (TRPM1
5?-GaaAcaAguCuuTggGaaA-3?, mGluR6 5?-GagAacAacCgcAggAacA 3?).
Probes were synthesized by Ribotask ApS, Odense, Denmark. Hybrid-
ization signals were detected by incubating the sections in blocking
buffer containing anti-fluorescein-alkaline phosphatase (AP) Fab frag-
ments (1:1000; Roche, Lewes, UK) for 1 hour at room temperature. AP
signal was detected by using a substrate kit (Vector Blue AP Substrate
Kit III; Vector, Burlingame, CA).
For details of sampling, RNA isolation, amplification, and PCR
conditions see van Soest et al.13PCR amplifications were carried out as
follows: mGluR6, 0.5 ?L DNA per 50 ?L, annealing temperature 52°C,
30 to 35 cycles; Ceacam, 1 ?L DNA per 25 ?L annealing temperature
52°C, 35 cycles; TRPM1, 1 ?L DNA per 25 ?L, annealing temperature
55°C, 40 cycles. All PCR experiments were amplified with ?-actin as
TRPM1-IR was present in the outer plexiform layer (OPL),
and the inner nuclear layer (INL) of the human retina.
TRPM1-IR formed two distinct patterns in the OPL: a punc-
tuated labeling (Fig. 2A, arrowhead) and a band-like labeling
(Fig. 2A, arrow). In the INL, TRPM1-IR labeled proximally
situated somata with protrusions running into the OPL (Fig
2A). The identity of cells expressing TRPM1 was determined
by double labeling experiments with cell type-specific mark-
In the OPL, TRPM1-IR colocalization was not evident with
the horizontal cell marker, calbindin (Fig. 2A, asterisk),
whereas it was with bipolar cell markers. TRPM1-IR colocal-
ized with the bipolar cell markers PKC?and PKC?(Figs. 2B and
2C). PKC?labels ON-bipolar cells whereas PKC?labels both
ON and OFF cone bipolar cell according to Kolb et al.,14
whereas Haverkamp et al.15suggests that the PKC?labeling is
restricted to OFF types. Both PKCs showed punctated- and
band-like labeling that both colocalized with TRPM1-IR (Figs.
2B and 2C; band-like labeling: arrow; punctated-like labeling:
arrowhead). The TRPM1 somatic labeling in the INL also colo-
calized with both PKCs (Figs. 2B, 2C, large arrow). The labeled
somata for PKC?and PKC?were localized in the same layer
directly below the horizontal cells in the distal part of the INL.
This suggests that both PKC?and PKC?label ON-bipolar cells
in the human retina. No colocalization of TRPM1-IR and
PKC?-IR and PKC?-IR was found in the IPL (Figs. 2B and 2C,
large arrow). This suggests that ON-bipolar cells axons do not
Combined, all the results outlined above suggest that the
somata and dendrites of ON-bipolar cells express TRPM1. The
band-like labeling could represent the bipolar cell invaginating
the cone terminals; the punctuated labeling could represent
the bipolar cell dendrites invaginating the rod spherule. To
evaluate this further, we studied the colocalization of TRPM1
with dendritically located components of the ON-bipolar cell
signaling cascade that have a close proximity to photoreceptor
synaptic ribbons: Goand mGluR6. We also investigated the
relation between TRPM1 and the pre-synaptic complex, using
two synaptic markers that label the synaptic ribbon, Ribeye
Double labeling experiments revealed TRPM1 and Goare
colocalized (Fig. 2D) and that both Ribeye-IR and Bassoon-IR
are strongly associated with TRPM1 (Figs. 2F and 2G). Dou-
between 150 kDa and 250 kDa. The expected weight for the TRPM1
antigen is 182 kDa. There is an additional band between 100 and 150
kDa, and a very weak band between 75 and 100 kDa. These bands most
likely represent degradation products of TRPM1.
Western blot analysis of TRPM1 antibody shows a band
IOVS, October 2011, Vol. 52, No. 11
TRPM1 in the Human Retina8357
(A) Double labeling of TRPM1 and the horizontal cell marker, calbindin (green). TRPM1-IR band-like (arrow) and
punctated-like labeling (arrowhead) was observed in the OPL. Somata in the inner nuclear layer (INL) also showed
Note that somatic TRPM1-IR and PKC?-IR is also present (large arrowhead). No colocalizatio between PKC?and
TRPM1 in IPL (large arrow). (C) TRPM1 double-labeled with the bipolar cell marker, PKC?. Colocalization of
Somatic colocalization was also observed (large arrowhead). TRPM1 does not colocalize with PKC?labeling of
bipolar cells synaptic terminals in the IPL (large arrows). (D) Double-labeling of TRPM1 and the G protein, Go.
Colocalization of TRPM1-IR and Go-IR occurred in the OPL (arrows). Note that in the somata of bipolar cells
(asterisk) TRPM1-IR (arrow) was separated from Go-IR (arrowhead). (E) Double-labeling of the metabotropic
glutamate receptor, mGluR6, and Go. Colocalization of mGluR6 and Gowas readily seen in the OPL (arrows). (F)
and sometimes colocalized (arrowhead) in the OPL. Note that no colocalization of TRPM1 and Bassoon was seen
in the IPL. (Inset): higher magnification showing that TRPM1-IR and Bassoon-IR are strongly associated. (G)
Double-labeling of TRPM1 and the synaptic ribbon marker, Ribeye. TRPM1-IR and Ribeye-IR are strongly associated
and sometimes colocalized. Scale bars, 5 ?m.
TRPM1 localization in the human retina; confocal immunofluorescence[b]. TRPM1 is labeled red.
8358 Klooster et al.
IOVS, October 2011, Vol. 52, No. 11
ble labeling experiments could not be performed with
TRPM1 and mGluR6 as both antibodies were raised in rabbit.
Instead we indirectly assessed the colocalization of TRPM1
and mGluR6 by double labeling mGluR6 and Go. As mGluR6
and Gowere found to colocalize (Fig. 2E) and as Goalso
colocalizes with TRPM1 (Fig. 2D) then it can be reasonably
assumed that TRPM1 and mGluR6 colocalize as well.
So far, our results suggest several aspects regarding the
location of TRPM1 in human retina. Firstly, TRPM1 is associ-
ated with both rod and cone ON-bipolar cells and is localized
to both the soma and dendrites. Secondly, dendritic TRPM1
colocalizes with Goand presumably with mGluR6 as well.
Thirdly, given the close proximity of Goand mGluR6 to pho-
toreceptor synaptic ribbons and the strong association with
Ribeye and Bassoon IR, TRPM1 is in close proximity to photo-
receptor synaptic ribbons. Combined this suggests that in hu-
man retina TRPM1 channels are located on the tips of ON-
bipolar cell dendrites, close to the synaptic ribbons of rods and
cones. This possibility was explored further at the ultrastruc-
Experiments performed at the ultrastructural level fo-
cused on the OPL. Ultrastructurally photoreceptor synapses
are triads with synaptic ribbons.18–20Rod spherules have
one ribbon and so can be easily distinguished from cone
pedicles, which have several ribbons. At the electron micro-
scopic level, TRPM1-IR was found on the triad’s central
elements, corresponding to bipolar cell dendrites, and was
located close to the synaptic ribbon in both cone pedicles
and rod spherules (Fig. 3). TRPM1-IR was never seen on
horizontal cell dendrites (H), the triad elements lateral to the
ribbons (Fig. 3). Surprisingly, ribbons in the rod spherules
occasionally showed TRPM1-IR (Fig. 3C) suggesting that
tion of TRPM1. (A) TRPM1-IR is lo-
cated at the central position in cone
pedicle. (B, C) TRPM1-IR is localized
at the bipolar cell dendrites ending
near the synaptic ribbon (R). Hori-
zontal cell dendrites (H) present in
the synaptic triads of cone pedicles
or rod spherules did not show
TRPM1-IR. Note that in (C) TRPM1-IR
is visible at the position of the synap-
tic ribbon (R). Scale bars, 0.5 ?m.
IOVS, October 2011, Vol. 52, No. 11
TRPM1 in the Human Retina8359
TRPM1 is located both post- and pre-synaptically in the rod
To confirm that TRPM1 can be synthesized by bipolar
cells and photoreceptors, ISH experiments were performed.
TRPM1-mRNA expression occurred in somata of the INL
(Fig. 4A) in a similar pattern observed for mGluR6-mRNA in
the INL (Fig. 4C) indicating the TRPM1-mRNA expressing
somata were ON-bipolar cells. In photoreceptor nuclei
mGluR6-mRNA expression was never seen whereas TRPM1-
mRNA could be clearly detected in some photoreceptor
nuclei (Figs. 4A and 4B, arrowheads). Some ganglion cells
showed an mGluR6-mRNA signal, which is consistent with
the work of Tehrani et al.21This signal was not studied
further in this study.
To confirm photoreceptors indeed express TRPM1, addi-
tional PCR experiments were performed. Pure photorecep-
tor samples were harvested with a laser dissection micro-
scope. They were used to study TRPM1 expression in
photoreceptors and compared with TRPM1 expression total
neural retina samples. The samples were taken from two
retinal eccentricities, centrally (c) just outside the macula
and peripheral to the large arteries (p). PCR detected
TRPM1-RNA in both the photoreceptor and total retina sam-
ples (Fig. 5A). The positive TRPM1 signal in the ONL sample
was not caused by bipolar cell contamination as mGluR6-
RNA was present only in the total neural retina (NR) sample
and not in the photoreceptor sample (Fig. 5B). To exclude
that the positive TRPM1 signal in the photoreceptors was
due to leaky expression, we determined the presence of
Caecam3-RNA. Caecam3 is abundantly present in blood cells
(Fig. 5B) but is not expressed in the retina.22We found
strong expression of Caecam3-RNA in blood samples (Fig.
5C, lane B) whereas there were no detectable signals in
photoreceptor samples (Fig 5C, lanes c and p), thus demon-
strating our detection threshold settings prevented the spu-
rious detection of leaky mRNA expression.
antisense TRPM1 RNA. Riboprobes
of TRPM1 (A, B) and mGluR6 (C). In
(A, C) TRPM1 and mGluR6 label cells
at the same position in the INL sug-
gesting bipolar cells express both
mGluR6 and TRPM1. In (A), the
TRPM1 riboprobe was also detected
in the somata of photoreceptors (ar-
rowhead). In (B), where the outer
nuclear layer (ONL) is shown at
higher magnification, TRPM1 ribo-
probe labeling of several photorecep-
tor somata is apparent (arrowheads).
In (C), the mGluR6 riboprobe is seen
to detect ganglion cells somata (aster-
isk) in addition to bipolar cells. Scale
bars, 10 ?m.
In situ hybridization of
8360 Klooster et al.
IOVS, October 2011, Vol. 52, No. 11
The present study ascertained the localization and expres-
sion pattern of TRPM1 in human retina using immunohisto-
chemistry, ISH, and PCR. In photoreceptor synapses TRPM1
is located postsynaptically, on the dendrite tips of ON-
bipolar cells near synaptic ribbons of both cone pedicles and
rod spherules, and pre-synaptically on ribbon of some rod
All proteins known to be involved in the initiation of the
ON-bipolar cell transduction cascade have now been shown in
the synaptic triads of cone pedicles and rod spherules. In
primate, mouse, and now human retina mGluR6,3NYX8and
Go,23and TRPM1, respectively, are found on the central ele-
ment of the triads close to the synaptic ribbons. This suggests
that all these proteins are situated in a single complex.
In addition to the dendritic labeling, we also observed
that the ribbon of some rod spherules had TRPM1-IR. This
indicates the TRPM1 protein is indeed present on (some)
synaptic ribbons. As this was a most unexpected finding we
confirmed the result with PCR and ISH experiments. How-
ever, despite the novelty of this result there is precedence
for TRP-channel localization on synaptic ribbons. Transient
receptor potential subfamily Vanniloid-1 (TRPV1) channels
have been found on photoreceptor ribbons in goldfish and
zebrafish.24These authors suggest the TRPV1 channels are
involved in docking the synaptic vesicles to the synaptic
ribbon or in the transport of synaptic vesicles along the
synaptic ribbon. However, it is clear that further experi-
ments are required to resolve the role of TRP channels in the
On average, the human retina contains 92 million rods25
and it is generally assumed that all rods are equal. However,
this may not be entirely true as we found some rods express
TRPM1 whereas others do not. In fish retina different types of
rods have been described based on their connectivity pat-
terns.26Most rods contact both horizontal and bipolar cells but
some rods only contact horizontal cells. Together these results
suggest that subclasses of rods exist in both the human and the
In humans, mutations in TRPM1 leads to congenital sta-
tionary night blindness (CSNB) type 1.7,9–11In these pa-
tients the ERG b-wave is absent while the a-wave remains
intact. The absence of b-wave indicates a deficiency of
ON-bipolar cell responses, which is consistent with a dis-
turbed mGluR6-TRPM1 cascade function. Our present re-
sults suggest that additional pre-synaptic modifications may
also be present. Such pre-synaptic modifications might not
be visible in the ERG of congenital stationary night blindness
type 1 patients because their remaining ERG signal consists
only of the a-wave, which is generated by the light response
of the photoreceptor’s outer segment and not by light-
induced vesicle release.
The authors thank Ton Put for preparing the photographs, Marcus
Howlett for his critical comments on the manuscript and correcting
the English, and the Corneabank Amsterdam for supplying the human
retinas (Director, Tama ´s Csiko ´s).
1. Boycott BB, Wa ¨ssle H. Parallel processing in the mammalian retina:
the proctor lecture. Invest Ophthalmol Vis Sci. 1999;40:1313–
2. Nawy S. The metabotropic receptor mGluR6 may signal through
G(o), but not phosphodiesterase, in retinal bipolar cells. J Neuro-
3. Morigiwa K, Vardi N. Differential expression of ionotropic gluta-
mate receptor subunits in the outer retina. J Comp Neurol. 1999;
4. Bellone RR, Brooks SA, Sandmeyer L, et al. Differential gene ex-
pression of TRPM1, the potential cause of congenital stationary
night blindness and coat spotting patterns (LP) in the Appaloosa
horse (Equus caballus). Genetics. 2008;179:1861–1870.
5. Shen Y, Heimel JA, Kamermans M, Peachey NS, Gregg RG, Nawy
S. A transient receptor potential-like channel mediates synaptic
transmission in rod bipolar cells. J Neurosci. 2009;29:6088–6093.
6. Morgans CW, Zhang J, Jeffrey BG, et al. TRPM1 is required for the
depolarizing light response in retinal ON-bipolar cells. Proc Natl
Acad Sci U S A. 2009;106:19174–19178.
7. Van Genderen MM, Bijveld MMC, Claassen Y, et al. Mutations in
TRPM1 are a common cause of complete congenital stationary
night blindness. Am J Hum Genet. 2009;85:730–736.
8. Gregg RG, Kamermans M, Klooster J, et al. Nyctalopin expression
in retinal bipolar cells restores visual function in a mouse model of
complete X-linked congenital stationary night blindness. J Neuro-
9. Audo I, Kohl S, Leroy BP, et al. TRPM1 is mutated in patients with
autosomal-recessive complete congenital stationary night blind-
ness. Am J Hum Genet. 2009;85:720–729.
10. Nakamura M, Sanuki R, Yasuma TR, et al. TRPM1 mutations are
associated with the complete form of congenital stationary night
blindness. Mol Vis. 2010;16:425–437.
11. Li Z, Sergouniotis PI, Michaelides M, et al. Recessive mutations of
the gene TRPM1 abrogate ON bipolar cell function and cause
complete congenital stationary night blindness in humans. Am J
Hum Genet. 2009;85:711–719.
12. Van den Pol AN, Gorcs T. Synaptic relationships between neurons
containing vasopressin, gastrin-releasing peptide, vasoactive intes-
tinal polypeptide, and glutamate decarboxylase immunoreactivity
in the suprachiasmatic nucleus: dual ultrastructural immunocyto-
chemistry with gold-substituted silver peroxidase. J Comp Neurol.
13. van Soest SS, de Wit GM, Essing AH, et al. Comparison of human
retinal pigment epithelium gene expression in macula and periph-
ery highlights potential topographic differences in Bruch’s mem-
brane. Mol Vis. 2007;13:1608–1617.
14. Kolb H, Zhang L, Dekorver L. Differential staining of neurons in
the human retina with antibodies to protein kinase C isozymes. Vis
15. Haverkamp S, Haeseleer F, Hendrickson A. A comparison of im-
munocytochemical markers to identify bipolar cell types in human
and monkey retina. Vis Neurosci. 2003;20:589–600.
16. tom Dieck S, Brandsta ¨tter JH. Ribbon synapses of the retina. Cell
Tissue Res. 2006;326:339–346.
PCR product was detected in photoreceptor (photo) and total neural
retina samples (retina). (B) mGluR6 PCR product was detected in the
(C) Ceacam3 PCR product was detected in blood cells (B), but not in
the photoreceptor samples. c, central; p, peripheral.
TRPM1 detected by PCR in photoreceptors[b]. (A) TRPM1
IOVS, October 2011, Vol. 52, No. 11
TRPM1 in the Human Retina8361
17. Schmitz F, Konigstorfer A, Sudhof TC. RIBEYE, a component of
synaptic ribbons: a protein’s journey through evolution pro-
vides insight into synaptic ribbon function. Neuron. 2000;28:
18. Linberg KA, Fisher SK. Ultrastructural evidence that horizontal cell
axon terminals are presynaptic in the human retina. J Comp
19. Dowling JE. The Retina. An Approachable Part of the Brain.
Cambridge: Belknap Press; 1987.
20. Missotte L. The synapses in the human retina. In: Rohen JW, ed.
The Structure of the Eye. Stuttgart: Schattauer-Verlag; 1965:
21. Tehrani A, Wheeler-Schilling TH, Guenther E. Coexpression pat-
terns of mGLuR mRNAs in rat retinal ganglion cells: a single-cell
RT-PCR study. Invest Ophthalmol Vis Sci. 2000;41:314–319.
22. Streichert T, Ebrahimnejad A, Ganzer S, Flayeh R, Wagener C,
Brummer J. The microbial receptor CEACAM3 is linked to the
calprotectin complex in granulocytes. Biochem Biophys Res Com-
23. Vardi N. Alpha subunit of Go localizes in the dendritic tips of ON
bipolar cells. J Comp Neurol. 1998;395:43–52.
24. Zimov S, Yazulla S. Localization of vanilloid receptor 1 (TRPV1/
VR1)-like immunoreactivity in goldfish and zebrafish retinas: re-
striction to photoreceptor synaptic ribbons. J Neurocytol. 2004;
25. Curcio CA, Sloan KR, Kalina RE, Hendrickson AE. Human pho-
toreceptor topography. J Comp Neurol. 1990;292:497–523.
26. Klooster J, Yazulla S, Kamermans M. Ultrastructural analysis of the
glutamatergic system in the outer plexiform layer of zebrafish
retina. J Chem Neuroanat. 2009;37:254–265.
8362 Klooster et al.
IOVS, October 2011, Vol. 52, No. 11