Golgi

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Golgi Flourens The reticular theory
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Cajal the neuron theory
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• The simplest analysis shows us that the nervous
  wave arising in cones and rods propagates
  afterward to bipolar and ganglionic elements.

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A fly in the ointment
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Cajal The paradox of HCs
We are obliged to admit that the visual signal
seized by these tangential neurons flows back,
toward the visual corpuscles ..photoreceptors..
somewhat far away, such as to constitute a kind
of vicious circle. Is it possible to admit
that nature has enabled an arrangement which
implies the destruction of the differentiation
power of cones and rods? Cajal Histologie du
Systeme Nerveux, 1909-1911
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Two things Cajal didnt take into account

• Neurons can be coupled in syncitia
• Connections between neurons can be inhibitory

Heinz Wassle
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Mammalian HCs
Type B cow
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Steve Massey
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Single type B axon terminal (rabbit)
Pan Massey, 2007
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Mouse only Type B HC
Alexa-fluor 488 injections
Cell body
CB
Dendritic syn. contacts
Axon terminal
AT
Axon terminal -detail
Schubert et al., J Neurophysiol 96, 1278,
2006 Shelley et al., Eur J Neurosci 23, 3176, 2006
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Turtle
In species with few rods, such as turtle, the
B-type cell axon terminal has sparse contacts
with red cones and the few rods that are there.
H1 soma-dendrites receive input from L cones
and feed back onto M cones whereas the terminal
receives input from L cones and rods and feeds
back onto L cones.
Leeper, 1978
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Fish
White perch
Lasater, J Neurophysiol 55,499, 1986
Type H2 HCs connect to green and blue cones
(biphasic), type H3 to blue cones only
(triphasic). H1 connect to all cones. Type H4
connect with rods only.
Dowling et al., Brain Res 360,331,1985
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Krizaj et al., J Comp Neurol, 2002
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The rod synapse the tetrad
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Synapse ultrastructure cone terminal the triad
Cone terminal in turtle
Turtle
Monkey terminal
Schwartz, E. A. Physiol. Rev. 82 875-891 2002
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Type A and B dendrites can contact cone terminals
in all combinations
All three possible combinations of HC dendrites
are present within a single cone terminal. A
Electron micrograph of a horizontal section
through a cone pedicle. The labeled lateral
elements originate from AHCs, and the unlabeled
elements are from BHCs. B-D show parts of A at
higher magnification. Presynaptic ribbons are
indicated with arrows. Scale bars 0.5 m in A
0.1 m in B-D.
Deng et al., J Comp Neurol 496, 698, 2006
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Fluorescent approach
Pan and Massey, 2007
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HCs hyperpolarize to light
Svaetichin, 1953
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Webvision
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Bloomfield Miller J Comp Neurol 1982
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Complication Chromatic HCs in turtle
Luminosity HC
Chromaticity red HC (inhibit. input from L,
excitatory from S and M cones)
Chromaticity yellow HC (inhib. input from L and
M, excitatory from S and UV cones)
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Fish Again
Webvision
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Luminosity and Chromaticity HCs in amphibians
Luminosity HC
Xenopus
Chromaticity HC
Witkovsky et al., PNAS, 1995
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The Stell model of spectral opponency
Horizontal cells are selective in output feeding
back only to cones of the next shorter wavelength
than represented by their inputs. Each H1 sends
its voltage changes with reversed polarity to
green cones, and each H2 sends its voltage
changes with reversed polarity to blue cones. As
a result, while H1 hyperpolarizes to all
wavelengths of illumination and with maximum
response to red wavelengths, H2 depolarizes to
red wavelengths and hyperpolarizes to green
wavelengths, and H3 hyperpolarizes to blue,
depolarizes to green, and hyperpolarizes to red
wavelengths.
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Glutamate Receptors
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Glutamate receptors in mammalian HCs
Whole-cell patch-clamp recordings of excitatory
amino acids-induced currents in a horizontal
cell. Currents induced by bath application of KA
(30 µm), AMPA (100 µm), GLU (100 µm) and NMDA
(500 µm) were recorded from an ALHC maintained at
a holding voltage of 70 mV. Blanco de la
Villa, Eur J Neurosci. 11, 867, 1999
Ionotropic-glutamate receptor agonists increased
calcium concentration in horizontal cells. Fura-2
fluorescence recorded from a dissociated
horizontal cell. Rivera et al., Visual Neurosci
18, 995, 2001
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iGluRs in rodent B-type HCs
Haverkamp et al., J Neurosci 21,2488,2001 Hack et
al., Eur J Neurosci 13, 15, 2001
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About 55 of AHC dendritic tips expressed AMPA
receptors, and 30 of AHC tips expressed kainate
receptors. On the other hand, 22 of BHC
dendritic tips expressed AMPA receptors and 33
of the tips expressed kainate receptors.
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Intrinsic properties signaling and CICR
(Calcium-Induced Calcium Release)
Linn Christensen, J Neurosci 12, 2156, 1992
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HC function Spatial processing
ON bipolar cell
Stone and Schutte, Visual Neurosci 7, 363, 1991
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Feedback I
Baylor et al., J Physiol 1971
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Feedback II
J.Physiol. 214, 265, 1971
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Feedback works by modulating the presynaptic
calcium current
Verweij et al., Vision Res 36, 3943, 1996
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Feedback IV primate cones
Verweij et al., J. Neurosci, 2003
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Verweij et al. 2003

• The spectral sensitivity of the feedback signal
  from horizontal cells to cones is much broader
  than the spectra of the cones ie, cant be based
  on one single cone type.

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The receptive field of the surround response
According to Packer and Dacey (2002), the RF of
primate HCs ranges from 300-600 um. This fits
well with the measured value of 451 um in
macaque cone surrounds.
Verweij et al., J Neurosci 23, 10249, 2003
Amplitude of cone surround response as a function
of stimulus radius. A, Membrane current of a cone
in response to spots of increasing radius. B,
Membrane current of a different cone in response
to annuli of increasing outer radii. Annulus
inner radius is 40 um. C, Response amplitudes
from A (), and B () plotted as a function of
stimulus outer radius. The continuous curves are
Equation 1 with r 12.6 pA and ? 59 um for the
filled symbols, and r 26.8 pA and ? 134 um
for the open symbols. RF -2 ? ln (0.1) 451
um.
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The chemical nature of HC feedback
Verweij et al., J. Neurosci, 2003
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Hemichannels?
Localization of Cx26 immunoreactivity. EM of
tangential sections of cone pedicles. (A) Control
section. SR, Synaptic ribbon. Arrows indicate HC
dendrites. (B) Cx26 immunoreactivity. (C)
Immunolabel is restricted to the HC dendrites.
Kamermans et al., Science 292, 1178, 2001
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A-type and B-type horizontal cells in the rabbit
retina have different dye-coupling properties.
OBrien et al., J. Neurosci 26, 1164, 2006
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Antibodies against Cx50 label dendritic junctions
on A-type horizontal cells.
Cx50 plaques occur where fine A-type horizontal
cell dendrites converge under cone pedicles. A,
A-type HCs were filled with Neurobiotin. Larger
Cx50 plaques occurred at the intersection of
major dendrites. Small Cx50 puncta occur where
fine dendrites meet. B, High-resolution view of a
terminal cluster (circle) underneath the cone
pedicle.
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B-type horizontal cells do not express Cx50
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Type B HCs in mouse express Cx 57
Cx 57 KO
wt
Hombach et al., Eur J Neurosci 19,2633, 2004
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Receptive Fields Length Constants

• Receptive fields are much larger than dendritic
  field. HC processes seldom cover more than
  100-200 um in diameter yet their RFs can attain
  diameters up to 5-6 mm.
• Length constant ? ?2 Rm/Ri where
• Rmmembrane resistance Ri internal
  (cytoplasmic) resistance

and V/Vo e-x/?
Nelson, J Comp Neurol 172,109, 1977
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Effects of Cx57 deletion on horizontal cell
coupling and receptive field size. (A) Length
constants of Cx57lacZ/lacZ (open squares n 10)
and Cx57/lacZ (half-filled squares n 8)
horizontal cells were significantly reduced
compared to wildtype horizontal cells (filled
squares n 18 P lt 0.05). (B) Tracer coupling
of Cx57lacZ/lacZ horizontal cells (n 14) was
significantly reduced compared to the wildtype (P
lt 0.001 n 8).
Shelley et al., 2006
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RF and HC coupling are modulated by light and
dopamine
dopamine
LY darkness
Turtle H1 HC axon terminals. Piccolino et al.,
PNAS, 1984
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Neuromodulation
Lasater Dowling, PNAS 82, 3025, 1985
Knapp et al., PNAS 87, 767, 1990
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Dopamine and rod-cone balance
rod
HC
D2
D1
Krizaj et al., 1993
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Feedforward
Mangel, J.Physiol. 1991
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Dilemma Amino acid signatures
R. Marc
R. Marc
Only H1 cells (red) have GABAergic signatures,
while H2 cells (blue) and H3 cells (green) have
non-GABAergic signatures.
Only H1 HCs transport GABA.
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Dilemma II exocytosis in HCs?
SNARE components in HC dendrites
calbindin
syntaxin IV

• cone

SNAP-25
Subcellular localization of syntaxin-4 to the
lateral elements within the triad synapse of both
rod (A, B) and cone (C, D) terminals.
syntaxin IV
Hirano et al. J Comp Neurol 2005 Hirano et al.
Visual Neurosci 2007
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Summary Horizontal Cells

• Are analog neurons respond to light in a graded
  fashion
• Responses are hyperpolarizing in mammals and can
  be depolarizing in lower vertebrates
• No spiking
• Are coupled by homotypic gap junctions AHCs,
  BHCs and ATs coupled separately
• Are huge and consequently have large RFs
• These RFs are modulated by light, dopamine, NO,
  retinoic acid, etc
• HC RFs form the RF surround in the excitatory
  vertical pathway
• HCs RFs sum the average luminance of the
  environment and subtract it from the signal. In
  this way they increase the spatial SNR.
• HCs are inhibitory interneurons inhibition is
  feedback and feedforward
• HCs mix rod and cone signals
• There are still many unknowns about the
  mechanism(s) through which RF is formed and
  modulated by HCs