An electroretinogram (ERG) records the change in electrical activity of a photoreceptor in response to light exposure. Whereas human photoreceptors are light-detecting cells in the retina that connect to a neuron, Drosophila photoreceptors themselves are the neurons. Therefore, ERGs are easily accessible in Drosophila. ERGs are used in mutant Drosophila to identify genes involved in phototransduction and neurodegeneration.

Pomona College

- Electroretinogram (ERG)
- Neuromuscular junction electrophysiology
- Giant-fiber-system recordings
- Wing injury assay


Nervous system assays in Drosophila

The retina is the light-sensitive lining at the back of the eye. It is composed of several layers of cells, including photoreceptors (rods and cones) and ganglion cells. When light enters the eye, it must pass through the layers of ganglion cells and other neurons before reaching the photoreceptors, which are located at the very back of the retina. The photoreceptors convert light into neural signals. A central area of the retina called the fovea is densely packed with cones and is responsible for sharp, detailed vision.

Retina

Ugur, B., Chen, K., & Bellen, H. J. (2016). Drosophila tools and assays for the study of human diseases. Disease Models & Mechanisms, 9(3), 235–244. https://doi.org/10.1242/dmm.023762

Drosophila tools and assays for the study of human diseases (2016)

Electroretinogram (ERG)

As NMJ electrophysiology is performed in third instar larvae, the method is not easily applied to longitudinal studies. The giant fiber system (GFS) in adult flies, however, is amenable to in vivo electrophysiology. Electrodes are applied to the eye, stimulating the giant fiber neurons in the brain. The GFS then activates the fly’s “flight” muscles in response to change in light exposure. GFS recordings have been used to study epilepsy and seizures.

Giant-fiber-system Recordings

Neuromuscular junction (NMJ) electrophysiology is performed on Drosophila third instar larvae to study human diseases characterized by abnormal electrophysiology, such as epilepsy and ALS. The larva is fileted down the length of its body to expose the ventral nerve cord and body wall muscles. Electrodes are then inserted into a motor neuron and a corresponding body wall muscle. This method of studying the NMJ is accurate, but difficult and labor-intensive, so electrophysiology is combined with genetic screens to fully characterize NMJ mutations.

Neuromuscular Junction Electrophysiology

The Drosophila wing injury assay is used to study axonal de-/regeneration in vivo. Cutting the wing severs the axon, causing axonal degeneration. However, after approximately a week, the injured axons regenerate by extending new sprouts toward the site of injury. Forward genetic screens can be combined with wing injury assays to identify genes responsible for axonal development.

Wing Injury Assay

The fovea is a small indentation in the retina where the lens focuses images to achieve the sharpest vision. It is characterized by a high density of specialized photoreceptor cells known as cones.

Fovea

Cells in the retina that detect light. 

* Rods
* Cones

Photoreceptors in the Retina

Ganglion cells are neurons located in the retina that receive visual signals from photoreceptors, such as rods and cones, via interneurons. The axons of these cells then converge and exit the back of the eye to form the optic nerve.

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