Retina amacrine cell
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||This article may be expanded with text translated from the corresponding article in the Czech Wikipedia. (April 2012)|
|Neuron: Amacrine cell|
|Location||INL of the retina|
|Function||inhibitory or neuromodulatory interneurons|
|Neurotransmitter||GABA, glycine, DA, or 5-HT|
|Presynaptic connections||Bipolar cells|
|Postsynaptic connections||Bipolar cells and Ganglion cells|
Amacrine cells are interneurons in the retina. Amacrine cells are responsible for 70% of input to retinal ganglion cells[Citation Needed]. 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 retinal ganglion cells form synapses. There are about 22 different types of amacrine cells, most lacking axons. 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.
They 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. Most are inhibitory using either GABA or glycine as neurotransmitters.
Relatively little is known of the functional roles of the amacrine cells. Amacrine cells with extensive dendritic trees are thought to contribute to inhibitory surrounds by feedback at both the bipolar cell, and ganglion cell levels. In this role they are considered to supplement the action of the horizontal cells. Amacrine cells give much more input to M (Magnocellular) ganglion cells than to P (Parvocellular) ganglion cells.
Other forms of amacrine cell are likely to play modulatory roles, allowing adjustment of sensitivity for photopic and scotopic vision. The AII amacrine cell (also known as the Rod amacrine cell) is a mediator of signals from rod cells under scotopic conditions.
Amacrine cells and other retinal interneuron cells are less likely to be near neighbours of the same subtype than would occur by chance, resulting in ‘exclusion zones’ that separate them. Mosaic arrangements provide a mechanism to distribute each cell type evenly across the retina, ensuring that all parts of the visual field have access to a full set of processing elements. MEGF10 and MEGF11 transmembrane proteins have critical roles in the formation of the mosaics by starburst amacrine cells and horizontal cells in mice. 
- Wassle, H.; Riemann, H. J. (22 March 1978). "The Mosaic of Nerve Cells in the Mammalian Retina". Proceedings of the Royal Society B: Biological Sciences 200 (1141): 441–461. doi:10.1098/rspb.1978.0026.
- Kay, Jeremy N.; Chu, Monica W., Sanes, Joshua R. (March 2012). "MEGF10 and MEGF11 mediate homotypic interactions required for mosaic spacing of retinal neurons". Nature. doi:10.1038/nature10877.
- Nicholls, John G.; A. Robert Martin, Paul A. Fuchs, David A. Brown, Mathew E. Diamond, David A. Weisblat (2012). From Neuron to Brain, Fifth Edition. Boston, Massachusetts: Sinauer Associates, Inc. ISBN 978-0-87893-609-0.
- Masland RH (2001). "The fundamental plan of the retina". Nat. Neurosci. 4 (9): 877–86. doi:10.1038/nn0901-877. PMID 11528418.
- Webvision amacrine cell article
- MeSH A08.663.358.050
- Eye Brain and vision book Hubel D (1988) Eye Brain and Vision, whole book available online.
- NIF Search - Amacrine Cell via the Neuroscience Information Framework