thumb|an orthographic cross-section of the layers of the human retina labeling various elements. amacrine cells are labeled near the top center

In the anatomy of the eye, amacrine cells are interneurons in the retina. They are named , because of their short neuronal processes. Amacrine cells are inhibitory neurons which project their dendritic arbors onto the inner plexiform layer (IPL). They interact with retinal ganglion cells and bipolar cells.

Structure

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, 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

  • Bipolar cell of the retina
  • Horizontal cell
  • Photoreceptor cell
  • Retinal ganglion cell

References

  • Webvision amacrine cell article
  • 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