Amacrine cell

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 at least 33 different subtypes of amacrine cells based just on their dendrite morphology and stratification. Like horizontal cells, amacrine cells work laterally, but whereas horizontal cells are connected to the output of rod and cone cells, amacrine cells affect the output from bipolar cells, and are often more specialized. Each type of amacrine cell releases one or several neurotransmitters where it connects with other cells. Another subtype of GABAergic amacrine cells are those that are dopaminergic. These are all TH expressing and these amacrine cells modulate light adaption and circadian rhythm. Around 15% of amacrine cells are neither GABAergic or glycinergic. Length of dendritic arbors: Based on length, spread of dendritic arbors, amacrine cells can be categorized as narrow field amacrine cells (around 70 micrometers in diameter), medium field amacrine cells (around 170 micrometers in diameter) and wide field amacrine cells (around 350 micrometers in diameter). MEGF10 and MEGF11 transmembrane proteins have critical roles in the formation of the mosaics by starburst amacrine cells and horizontal cells in mice. ==Function==

In many cases, the subtype of the amacrine cell speaks to its function (form leads to function), but some specific functions of the retinal amacrine cells can be outlined. • Intercept retinal ganglion cells and/ or bipolar cells in the IPL • Through their connections with other retinal cells at synapses and release of neurotransmitters, contribute to the detection of directional motion, modulate light adaption and circadian rhythm, and control high sensitivity in scotopic vision through connections with rod and cone bipolar cells There is still much to be discovered about all of the different functions of all of the different 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. Other forms of amacrine cell are likely to play modulatory roles, allowing adjustment of sensitivity for photopic and scotopic vision. The AII amacrine cell is a mediator of signals from rod cells under scotopic conditions. == Classification ==

It was previously thought that all types of amacrine cells lack an axon. This is true for most amacrine cells; their dendrites contain input and output synapses, but they lack an axon. However, some types of amacrine cells have long axon-like processes that they use to integrate signals over long distances within the retina, but these do not exit the retina like ganglion cell axons. According to a more recent form of classification of the neuronal layer of the retina, amacrine cells that have an axon are distinguished as a separate class of axonal cells, which, together with amacrine and ganglion cells, belong to the superclass of multipolar neurons. ==See also==