AII amacrine cells

File:Structure rods cones.png

Cone verses rod photoreceptor.

AII amacrine cells are a subtype of amacrine cells. Amacrine cells are neurons that exist in the retina of mammals to assist in interpreting photoreceptive signals. AII amacrine cells serve the critical role of transferring light signals from rod photoreceptors to the retinal ganglion cells (which contain the axons of the optic nerve). The AII amacrine cells are unique because they work primarily with the vertical transmission of information, meaning they connect the bipolar and ganglion cells. Other amacrine cells primarily assist with horizontal pathways, meaning they connect similar types of neurons. The Classical Rod Pathway describes the role of AII amacrine cells in the mammalian retina. This can be summarized as follows:

• Scotopic lighting is dim lighting. The mammalian eye primarily utilizes its rod shaped photoreceptors to interact with this light.
  • Photoreceptors contain photopigments. These units contain one protein, known as opsin, and one molecule, known as a chromophore. The chromophore of vertebrate animals is retinal, a form of Vitamin A.
• When photons of light reach the retina, they are absorbed by the chromophore. This causes a change of configuration, which causes a signaling pathway that results in the closure of membrane sodium channels. This change triggers the cell membrane to become charged negatively through the process of hyperpolarization.
• The chromophore and opsin detach, reverting the chromophore to its original conformation.
  • This step is the main difference between this vertebrate pathway and the invertebrate pathway. In invertebrates, the chromophore is rarely reused. Instead, new chromophores are generated for the next use.

    File:11-cis-Retinal Vitamin A-Aldehyd.svg

    The conformation change of retinal, caused by light.

• The rod photoreceptor synapses with the rod bipolar cell.
• This rod bipolar cell will directly (exclusively) synapse with an AII amacrine cell in sublamina B (within the inner plexiform layer)
• The AII amacrine cells becomes activated (i.e., it depolarises) when light stimulates a rod.

(Once activated, the AII amacrine cell then modulates the cone ON and OFF channels):

• In sublamina B, the dendrites of the AII amacrine cell also form gap junctions with:

1. Other AII amacrine cells
2. ON-cone bipolar cells

• In sublamina A, the dendrites of the AII amacrine cell usually form inhibitory glycinergic synapses onto the OFF-cone bipolar cells

The ON- and OFF- cone bipolar cells in turn contact the ON- and OFF-centre retinal ganglion cells, respectively. Note: A small proportion of rods contact the cone bipolar cells directly. Photopic lighting is brighter lighting. The mammalian eye primarily uses its cone shaped receptors for this light.