Difference between revisions of "Amacrine Cell"

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===Molecular markers===
 
===Molecular markers===
There exist several molecular markers for amacrine cells, including ''Pax6'', ''Tcfap2b'', ''Gad1'', and ''GlyT1''.<ref> Cherry, T. J., Trimarchi, J. M., Stadler, M. B. & Cepko, C. L. [http://www.pnas.org/content/106/23/9495.full Development and diversification of retinal amacrine interneurons at single cell resolution]. ''PNAS'' '''106''' (23), 9495-9500 (2009).</ref>  
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There exist several molecular markers for amacrine cells, including ''Pax6'', ''Tcfap2b'', ''Gad1'', and ''GlyT1''.<ref name="Cherry 2009">{{cite journal  | author=T. J. Cherry; J. M. Trimarchi; M. B. Stadler; C. L. Cepko |title=Development and diversification of retinal amacrine interneurons at single cell resolution |journal=PNAS |volume=106 |issue=23 |pages=9495–9500 |year=2009 |urlhttp://www.pnas.org/content/106/23/9495.full }}</ref>
However, no markers exclusively expressed in amacrine cells are known to exist, and there exist "far fewer molecular markers [for amacrine cells] than known morphological types" of amacrine cells.<ref> Cherry, T. J., Trimarchi, J. M., Stadler, M. B. & Cepko, C. L. [http://www.pnas.org/content/106/23/9495.full Development and diversification of retinal amacrine interneurons at single cell resolution]. ''PNAS'' '''106''' (23), 9495-9500 (2009).</ref>
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However, no markers exclusively expressed in amacrine cells are known to exist, and there exist "far fewer molecular markers [for amacrine cells] than known morphological types" of amacrine cells.<ref name="Cherry 2009">{{cite journal  | author=T. J. Cherry; J. M. Trimarchi; M. B. Stadler; C. L. Cepko |title=Development and diversification of retinal amacrine interneurons at single cell resolution |journal=PNAS |volume=106 |issue=23 |pages=9495–9500 |year=2009 |urlhttp://www.pnas.org/content/106/23/9495.full }}</ref>
  
 
===Neurotransmitters===
 
===Neurotransmitters===

Revision as of 02:45, 31 March 2012

File:A2.png
A type of amacrine cells, called AII, reconstructed from EyeWire.

Amacrine cells are interneurons in the retina. Amacrine cells are responsible for 70% of input to retinal ganglion cells. Bipolar cells, which are responsible for the other 30% of input to retinal ganglia, are regulated by amacrine cells.

Amacrine cells operate at the inner plexiform layer (IPL), the second synaptic retinal layer where bipolar cells and ganglion cells form synapses. There are about 40 different types of amacrine cells and are classified by the width of their field of connection, which layer(s) of the stratum in the IPL they are in, and by neurotransmitter type. No single type of amacrine cell predominates; the type with most frequency is observed only 13% of total population, and the remainders are distributed among many types of cell, each making up 5% or less of the total amacrine cell population. The average diameter of dendritic field for each type varies over 34 to 400 microns, and their overall shapes alone are enough to serve as criterion of classification.

There is no clear distinction between dendrites and axons in the processes of most of the amacrine cells, though they are often referred to as dendrites in general.

Like horizontal cells, amacrine cells work laterally affecting the output from bipolar cells, however, their tasks are often more specialized. Each type of amacrine cell connects with a particular type of bipolar cell, and generally has a particular type of neurotransmitter. One such population, AII, 'piggybacks' rod bipolar cells onto the cone bipolar circuitry. It connects rod bipolar cell output with cone bipolar cell input, and from there the signal can travel to the respective ganglion cells.

Most are inhibitory using either GABA or glycine as neurotransmitters.

Physiology

Visual Response Properties

A few types of amacrine cells are associated with their respective functions and with corresponding ganglion cells. For example, starburst amacrine cells (SACs) are known to make synapses onto on/off direction-selective ganglion cells (On/Off DSGCs) [1], and wide-field (WF) amacrine cells, also known as polyaxonal amacrine cells, are considered to be associated with object motion sensitive ganglion cells either directly or indirectly via bipolar cells [2].

Cellular Biophysics

Anatomy

Location

File:Amacrine cells.png
Narrow-field amacrine cells

Amacrine cells have their cell bodies located in the inner nuclear layer of the retina and have projections in the inner plexiform layer. Different subtypes of amacrine cells project differently in the inner plexiform layer[3], as shown in the figure to the right depicting different types of narrow-field amacrine cells.

Shape

File:Ac types.png
Two amacrine cells with distinctive shapes. They can be easily mapped to their respective class in the catalog.

Amacrine cells send projections from their cell bodies into the inner plexiform layer. These projections arborize differently for different subtypes of amacrine cells. Amacrine cells have these projections distributed rouhgly circularly in the inner plexiform layer, though some subtypes arborize asymmetrically. Most amacrine cells can be classified according to the diameter of their projection arborization: "narrow-field" cells have arbors less than 125 µm in diameter, "medium-field" cell arbors range from 125 to 400 µm in diameter, and "wide-field" cell arbors are larger than 400 µm.[3]

Their overall shapes alone are enough to serve as criterion for the classification.

Connections

Amacrine cells have their postsynaptic targets in the inner plexiform layer. Amacrine cell dendrites are known to synapse onto ganglion cell neurites in the IPL, mediating "antagonistic inputs from bipolar cells in the gancglion cell's surround." (Kandel)

Molecules

Molecular markers

There exist several molecular markers for amacrine cells, including Pax6, Tcfap2b, Gad1, and GlyT1.[4] However, no markers exclusively expressed in amacrine cells are known to exist, and there exist "far fewer molecular markers [for amacrine cells] than known morphological types" of amacrine cells.[4]

Neurotransmitters

Most amacrine cells are inhibitory and secrete GABA or glycine, though in total, amacrine cells as a class use eight different neurotransmitters (Kandel). A particular class of amacrine cells—the starburst amacrine cell—has been found to be both cholinergic and GABAergic.[5]

History

Open questions/status/relevance to Eyewire

References

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  5. O’Malley, D. M., Sandell, J. H. & Masland, R. H. Co-release of acetylcholine and GABA by the starburst amacrine cells. J. Neurosci. 12 (4), 1394–1408 (1992).