A18 is a neuron found in the retina.
A18 neurons are wide-field dopaminergic amacrine cells. Like other amacrine cells, A18 neurons are located in the IPL and lack axons, but possess an extensive web of dendrites. A18 neurons use dopamine as a neurotransmitter. 
Neuronal Type: Interneuron
A18 neurons are located in the inner plexiform layer in the retina. The dendrites of A18 neurons are close to the dendrites and cell bodies of AII, A8, A17, and maybe A13 as well  but do not connect with ganglion cells in mammals.  These neurons do not have axons, but their dendrites can transmit signals to other cells.  A18 dendrites form a complex web with few ring-like spaces.  The cell bodies are approximately 15 um. 
- Neurotransmitter: Dopamine
A18 neurons synapse with other amacrine cells.
A18 neurons receive input mostly from other amacrine cells and also from an as yet unidentified cone bipolar cell type. 
A18 neurons are thought to send signals to AII amacrine cells, which then signal ganglion cells. 
This type of amacrine neuron may play a role in adapting to changes in lighting conditions.