Electroretinogram (ERG) Measurements in Larval Zebrafish

INTRODUCTIONThe electroretinogram (ERG) is an electrophysiological tool used to measure electrical activity originating in the outer retina in response to a light stimulus. Defects occurring at various levels of the retina can easily be detected by ERG measurements. Furthermore, the shape of the ERG response points toward the likely retinal cell type responsible for the deficit. Thus, this method is particularly useful for a rapid assessment of retinal function in genetically or pharmacologically manipulated animals. A typical ERG curve can be subdivided into three components: a small initial a-wave originating in photoreceptor activity, a large positive b-wave reflecting mainly ON bipolar cell depolarization, and a d-wave occurring at light offset. Here we present a noninvasive protocol for taking ERG measurements in larval zebrafish (4-7 days post-fertilization [dpf]). We use an extracellular recording electrode which is placed onto the surface of the cornea of the larva, and a light flash of a defined intensity and duration which is applied to evoke a response. In a typical larval ERG trace, we are able to record ERG a-, b-, and d-waves.