Difference Between Amacrine and Horizontal Cells

The key difference between amacrine and horizontal cells is that amacrine cells receive information from the bipolar cells while horizontal cells receive information from photoreceptors.

Photoreceptors, bipolar cells, ganglion cells, horizontal cells and amacrine cells are the five types of neurons found in our retina. All these neurons contribute to the processing of visual information in the retina. Photoreceptors, bipolar cells and ganglion cells participate in the most direct route for transmitting visual information to the brain. Horizontal cells and amacrine cells mediate lateral interactions in the outer and inner plexiform layers, respectively. Horizontal cells receive information from photoreceptors while amacrine cells receive their inputs from bipolar cells.

CONTENTS

1. Overview and Key Difference
2. What are Amacrine Cells
3. What are Horizontal Cells
4. Similarities Between Amacrine and Horizontal Cells
5. Side by Side Comparison – Amacrine vs Horizontal Cells in Tabular Form
6. Summary

What are Amacrine Cells?

Amacrine cells are a type of interneuron in the retina involved in the retina’s indirect pathway. Their cell bodies are located in the inner nuclear layer. They operate at the inner plexiform layer. Amacrine cells receive inputs from bipolar cells, and then connect bipolar cells to ganglion cells. Therefore, amacrine cells are postsynaptic to bipolar cell terminals and presynaptic to the dendrites of ganglion cells. There are 30 to 40 different sub-types of amacrine cells. Similar to horizontal cells, amacrine cells work laterally. However, unlike horizontal cells, amacrine cells are more specialized. They release neurotransmitters.

What are Horizontal Cells?

Horizontal cells are a type of interneurons in the retina that work laterally similar to amacrine cells. Their cell bodies are also located in the inner nuclear layer and they operate at the outer plexiform layer. Horizontal cells receive inputs from multiple photoreceptors. Horizontal cells depolarize by the release of glutamate from photoreceptors.

Horizontal cells mainly modulate the information from the photoreceptors to bipolar cells in the outer plexiform layer. There are one or two classes of horizontal cells.

What are the Similarities Between Amacrine and Horizontal Cells?

• Amacrine and horizontal cells are two types of cells that contribute to the processing of visual information in the retina.
• Structurally, they are retinal neurons.
• They are interneurons.
• They work laterally.
• They have their cell bodies in the inner nuclear layer of the retina.
• Moreover, they are inhibitory neurons.

What is the Difference Between Amacrine and Horizontal Cells?

The key difference between amacrine and horizontal cells is that the amacrine cells are a type of retinal interneurons that modulate the information from bipolar cells to retinal ganglion cells in the inner plexiform layer. Horizontal cells, on the other hand, are a type of retinal interneurons that modulate the information flow from photoreceptors to bipolar cells in the outer plexiform layer. Moreover, the amacrine is responsible for providing an alternate pathway by connecting bipolar cells with ganglion cells, while horizontal cells, on the other hand, are responsible for the visual system’s sensitivity to luminance contrast over a wide range of light intensities.

Below infographic shows more details of the difference between amacrine and horizontal cells.

Summary – Amacrine vs Horizontal Cells

Amacrine cells and horizontal cells are two types of interneurons in the retina that are primarily responsible for lateral interactions within the retina. Amacrine cells receive inputs from bipolar cells while horizontal cells receive inputs from photoreceptors. Thus, this is the key difference between amacrine and horizontal cells. Amacrine cells operate at the inner plexiform layer in the retina while horizontal cells operate at the outer plexiform layer. Both are found in the inner nuclear layer of the retina and they involve in the lateral connections or the retina’s indirect pathway.

Reference:

1. Purves, Dale. “The Retina.” Neuroscience. 2nd Edition., U.S. National Library of Medicine, 1 Jan. 1970, Available here.
2. Kolb, Helga. “Roles of Amacrine Cells.” Webvision: The Organization of the Retina and Visual System [Internet]., U.S. National Library of Medicine, 30 Apr. 2007, Available here.

Image Courtesy:

1. “Amacrine” By Decembrini – cropped by me from Decembrini et Al. PLOS Biology [1] (CC BY 2.5) via Commons Wikimedia
2. “Gray882” By Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body (See "Book" section below)Bartleby.com: Gray's Anatomy, Plate 882, Public Domain) via Commons Wikimedia