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I. Photoreception; receptor cells nourished by pigment epithelium II. Connectivity and function of horizontal, bipolar and amacrine


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2011.10.14.. TÁMOP – 4.1.2-08/2/A/KMR-2009-0006 1 Development of Complex Curricula for Molecular Bionics and Infobionics Programs within a consortial* framework**

Consortium leader


Consortium members


The Project has been realised with the support of the European Union and has been co-financed by the European Social Fund ***

**Molekuláris bionika és Infobionika Szakok tananyagának komplex fejlesztése konzorciumi keretben

***A projekt az Európai Unió támogatásával, az Európai Szociális Alap társfinanszírozásával valósul meg.


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By Imre Kalló

Contributed by: Tamás Freund, Zsolt Liposits, Zoltán Nusser, László Acsády, Szabolcs Káli, József Haller, Zsófia Maglóczky, Nórbert Hájos, Emilia Madarász, György Karmos, Miklós Palkovits, Anita Kamondi, Lóránd Erőss, Róbert

Gábriel, Kisvárdai Zoltán


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Imre Kalló & Róbert Gábriel

Pázmány Péter Catholic University, Faculty of Information Technology

I. Photoreception; receptor cells nourished by pigment epithelium II. Connectivity and function of horizontal, bipolar and amacrine


III. Ganglion cells and the visual pathway.


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Anatomy of the visual organ.

Optic disc  Optic nerve  Fovea centralis 

Retina  Sclera 


Ciliary body  Posterior chamber 

Anterior eye chamber Aqueous humour 




Suspensory ligaments of the lens 

Vitreous humour  Lens 


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Anatomy of the visual organ.

The human visual organ is a paired, light-proof „box” (eyeballs) with an adjustable diameter pinhole (pupil) on the front side. Light is passing through transparent media in front (i.e. tear, cornea, aqueous humor) and behind (i.e. the lens, vitreous humor) the pupil to reach the inner layer of the eyeball (retina), where the energy of light is converted to chemico-electric impulses. Light from objects located between 25 cm to far distances is focused onto the retina by the adjustment of lens convexity. The inverted image of the objects projected to the retina, however can be processed at high resolution only at the central fovea, where light reaches the cone receptor cells directly.


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Histology of the retina

ƒ10 histologically distinguishable layers

ƒ4 layers of cell bodies (nuclei) 1 layer of pigment cells 1 layer of receptor cells 2 layers of neurons

ƒ2 layers of synapses

ƒVertical ″through pathway”

ƒHorizontal influence on the information processing


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Connectivity of basic cell types of the retina

Rods and cones


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Path of the light in the eye


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Photoreceptor cells: anatomy

ƒDuplex retina


one (or maybe two) types similar morphology

long outer segment

closed endomembrane system


three, four types – wave-length sensitivity varies from group to group

open endomembrane system


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Synapses established by the photoreceptor cells I.


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Synapses established by the photoreceptor cells II.

ƒ Inner segment

ƒ Photoreceptor cell terminal

ƒ „Ribbon” synapse

Two pools of synaptic vesicles

Presynaptic markers (eg. bassoon, rib eye)

ƒ Postsynaptic triad


Dendrite of the bipolar cells in the middle, processes of horizontal cells laterally


„Invaginating” and „flat” connections


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Photoreceptor cells


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Types of photoreceptor cells

Class of cells Types of cells Subtypes Notes

Photoreceptor Cells

Rods Uniform

There are green and red light-sensitive rods in amphibians


Cones sensitive for short wave-length light

There are UV- sensitive cones in certain species Cones sensitive for

long wave-length light

Two (green and red) subgroups of cones in primates


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Outer segment events: photochemical reaction


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Outer segment events: sodium channels close - hyperpolarization


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Absorbance maximum of photoreceptor cells


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Light sensitivity of photoreceptors


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Microanatomy of bipolar cells

ƒ Orientation of bipolar cells:

dendritic tree is towards the photoreceptor cells, axon is in the inner plexiform layer (IPL)

ƒ It connects the external and internal parts of the retina

ƒ It is crucial for processing the visual information

ƒ 10 different types of bipolar cells are known in vertebrates


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Types of bipolar neurons

ƒ Rod-bipolar cells: there are only in mammals

ƒSignificance: visual reception at low light intensity circumstances

ƒCone-bipolar cells: their sensitivity varies according to the wave-length

ƒDepolarizing cells (ON-type)

ƒHyperpolarizing cells (OFF-type)

ƒCells with special receptive field

Class of cells Types of cells Subtypes Notes

Bipolar Cells

Rod-bipolar cells Uniform Bipolar neurons of amphibians receive afferents from both cones and rods. In a few species there are blue bipolars.

ON-type cone- bipolar cells

Many algroups OFF-type cone-

bipolar cells

Many algroups


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Bipolar neurons


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Neurochemistry of bipolar neurons

ƒ Rod-bipolars:


ƒ Cone-bipolars:

OFF: recoverin ON: mGLUR6

ƒ Neurotransmitters used:

Glutamic acid

ƒ Axon terminals:

L-type VGCCa


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Synaptic connections of bipolar cells in the inner plexiform layer I.

ƒ Axons, ribbon synapses

ƒ One terminal contains several ribbons, and establishes several outputs

ƒ Every 8-10th synapse of the inner plexiform layer is established by bipolar cells

ƒ Postsynaptic diad


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Synaptic connections of bipolar cells in the inner plexiform layer II.

ƒ Bipolar axons terminals also receive afferents (from amacrine cells)

ƒ Most of the output is glutamatergic, in contrast the inputs are


ƒ Axon terminals of the bipolar

neurons contains both GABAA and GABAB receptors


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Synaptic connections of bipolar cells in the inner plexiform layer III.


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Physiology of bipolar cells

ƒ Hyperpolarising cells:

AMPA and KA receptors, sign- conserving OFFcells

ƒ Depolarising cells:

mGLUR6 receptors, sign-inverting


ƒ ON-OFF cells: only in non-mammal vertebrates


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Bipolar neurons are sensitive to the size of the enlightened area

ƒ Transient response turns into sustained response

ƒ Inhibition originating from the surrounding area decreases (see center/surround organisation)

ƒ Saturation


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Microanatomy of the horizontal cells

Class of cells

Types of cells

Subtypes Notes

Horizontal Cells

Cells with axon

Uniform group

Many species have also chromatic horizontal

cells Cells

without axon

Uniform group


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Physiology and neurochemistry of the horizontal cells

ƒ Hyperpolarizing and depolarizing cells

ƒ Both cell types contain ionotropic glutamate receptors

ƒ Neurotransmitter of the horizontal cells is GABA

ƒ Histological marker of the horizontal cells is either PA or CaBP

ƒ Lateral inhibition, centre-surround organization


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Light on center


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Light on surround


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Cells of the inner part of the retina I.

Class of cells Types of cells Subtypes Notes

Amacrine Cells

Cells with wide dendritic field- cells with narrow dendritic field

Several subgroups from morphological,

physiological and neurochemical point

of view

The second column lists classification

categories Cells with axon-

cells without axon Cells generating action potential – cells generating only local potential change

Cells located in normal position –

Cells displaced


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ƒ Bipolar cells

ƒ Amacrine cells

ƒ Ganglion cells

ƒ Glial cells:

Müller-cells (K-sipho model)

ƒ A>A, B>A, A>B, B>G and A>G synapses

ƒ High complexity

Cells of the inner part of the retina II.


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Microanatomy of amacrine cells I.

ƒ Cells with narrow and wide dendritic tree

ƒAbout 20-30 different cell types

ƒMosaic organization within the retina


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ƒ There are cells without axons, as well as ones with multiple axons (poliaxonal cells)

ƒ Diffuse network of processes

ƒ Many different neurotransmitters, frequent co-localisations

ƒ Sublayers in the inner plexiform layer (uni-, bi-, tri- and multistratified cells)

Microanatomy of amacrine cells II.


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Neurochemistry of amacrine cells I.

ƒ Most of the cells use GABA or glycine, show narrow dendritic tree, and

establish multiple synapses – 90% of all amacrine cells

major role is inhibition!!!!

ƒ Cells with medium-sized dendritic tree:

acethylcholine (4-6%) orientation-selectivity detection of movement

starburst” cells: philogenetically conserved cells

Neurochemical code system!


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Neurochemistry of amacrine cells II.

ƒ Monoamines: DA, 5-HT

ƒ Peptidergic cells: SP, NPY, CCK; most cases these peptide are present as co- transmitter with GABA or glycine


Usually they are uni- or bistratified cells


Their functions: neuromodulation,

eg. light adaption


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Neurochemistry of amacrine cells III.: Calcium binding proteins


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Physiology of amacrine cells

ƒ Sustained and transient On, Off and On-Off

ƒ Sublaminar distribution of the dendrites is in overlap with the axonal

ramifications of the bipolar cells and the dendritic tree of the ganglion cells.

ƒ Overlap of the morphological and physiological segregation

ƒ Orientation selectivity


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Amacrine cells I.


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Amacrine cells II.


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Amacrine cells III.


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Amacrine cells IV.


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Amacrine cells V.


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Synapses of the inner plexiform layer


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Microanatomy of ganglion cells

ƒ Mass filling, HRP injection in the eye

ƒ Mozaics of cells

ƒ Dendritic segregation of On and Off cells

ƒ On-Off cells are present frequently, especially in lower vertebrates


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Neurochemistry of ganglion cells

ƒ Neurofilament proteins

ƒ MAPs

ƒ On the receiving side:

ionotropic and metabotropic glutamate receptors (AMPA, NMDA)

ƒ IP3 and RyR systems

ƒ Calciumbinding proteins

ƒ Neurotransmitter: glutamic acide, certain cells contain neuropeptides (SP, NPY, PACAP): target-specificity!


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Physiology of ganglion cells I.


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Microphysiology of ganglion cells II.

•Generation of spikes

•Saturation, long-lasting after potentials

•Plateau phase, oscillations

•X, Y and W cells – anatomy can be brought in correspondence with electrophysiology characteristics

ƒMosaics of ganglion cells, convergence!


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Microphysiology of ganglion cells III.

ƒ Tranzient ganglion cells can exhibit both ON and OFF characteristics

ƒ Ganglion cells are under

GABAergic inhibition. Inhibition is mediated through GABAA



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Centre-surround organization

ƒ Dendritic field, receptive field

ƒ Lateral inhibition

ƒ Horizontal cells, GABA

ƒ Amacrine cells, GABA and glycine

ƒ On-centrum, off-centrum


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Communication with higher order visual centres


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Mozaic of developing retina

Development of central specialization begins already at early stage of



The extent of specialization may vary

from animal to animal depending on

the territory they occupy


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A special mozaic of ganglion cells

ƒ Elephant: Perpendicular and horizontal specializations

ƒ Horizontal is present to observe continously the trunk at the highest resolution

ƒ Primates: central fovea

- there are no rods at this site - bipolar cell-ganglion cell

connection is in 1:1


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Central mechanisms of vision


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The lateral geniculate body (CGL, LGN)


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Receptive fields of CGL and V1 cells


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Retinal projection to the visual cortex


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Thank you for your attention


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• Inner plexiform layer – contains the synapse between the bipolar cell axons and the dendrites of the ganglion and amacrine cells.. • Inner nuclear layer – contains the nuclei