Definition:

Amacrine cells are a type of inhibitory interneuron found in the retina of vertebrate animals.

Characteristics:

  • Location: Amacrine cells reside within the inner nuclear layer of the retina, specifically in the proximal inner nuclear layer.
  • Morphology: These cells have a narrow, elongated dendritic tree that extends both vertically and horizontally within the retina.
  • Connections: They form synapses with other retinal neurons, such as bipolar cells, ganglion cells, and other amacrine cells, allowing for complex circuitry within the retina.
  • Neurotransmitters: Amacrine cells use various neurotransmitters, including gamma-aminobutyric acid (GABA), glycine, and glutamate, to modulate neural signaling.
  • Function: These cells play a vital role in lateral inhibition, contrast enhancement, and the integration of visual signals to refine visual information before it reaches ganglion cells and is transmitted to the brain.

Types:

Amacrine cells are classified into different types based on their neurotransmitter content, connectivity, and response properties. Some common types include:

1. GABAergic Amacrine Cells:

GABAergic amacrine cells release gamma-aminobutyric acid (GABA) as their main neurotransmitter and play a crucial role in the modulation of inhibitory signals in the retina.

2. Glycinergic Amacrine Cells:

Glycinergic amacrine cells release glycine as their main neurotransmitter and are involved in inhibitory neurotransmission in the retina. They are particularly important in shaping visual responses and controlling excitability in retinal circuits.

3. Dopaminergic Amacrine Cells:

Dopaminergic amacrine cells release dopamine and participate in the regulation of various retinal functions, including light adaptation, modulation of photoreceptor sensitivity, and adjustment of retinal responses to changing light conditions.

4. Cholinergic Amacrine Cells:

Cholinergic amacrine cells release acetylcholine, modulating neural activity in the retina and playing a role in processes such as contrast sensitivity, visual processing, and regulation of visual information flow.

These are just a few examples, as there are numerous subtypes of amacrine cells with diverse functions and characteristics.