Examination of the Unusual ERG Components of Young Zebrafish

Abstract

Abstract: : Purpose: The electroretinogram (ERG) waveform of young zebrafish in response to short–wavelength stimuli (320–480 nm) consists of a large voltage–negative potential at stimulus onset followed later by a voltage–positive b–wave, while the ERG to long–wavelength stimuli (500–640 nm) consists primarily of a voltage–positive b–wave to stimulus onset. This study examined the nature of this wavelength–dependent voltage–negative response in young zebrafish. Methods: ERGs were obtained from light–adapted young (6–21 days postfertilization) and adult (1 year or older) zebrafish (Danio rerio) to 200 ms flashes of various wavelengths and irradiances. Log irradiance versus response amplitude functions of the ERG response at various post–stimulus–onset times (e.g., 50, 75 & 150 ms following stimulus onset) were derived as well as spectral sensitivity functions. Aspartate, and a combination of APB (DL–2–amino–4–phosphonobutyric acid) and PDA (cis–2,3–piperidinedicarboxylic acid), were applied to the eye to suppress the responses of various types of retinal neurons, leaving primarily photoreceptor activity. Results: In adults, the irradiance vs. response function slopes were positive regardless of stimulus wavelength and post–stimulus–onset time. In young zebrafish, the slopes of the irradiance vs. response functions were negative to short–wavelength stimuli at short post–stimulus–onset times (i.e., 75 ms following stimulus onset), and positive at longer post–stimulus–onset times (e.g., 150 ms following stimulus onset). The slopes of the functions to long–wavelength stimuli were positive at all post–stimulus–onset times. Aspartate eliminated voltage–positive responses; the irradiance vs. response function slopes were negative regardless of stimulus wavelength and post–stimulus–onset times. In addition, these functions were similar to the functions of normal young fish to short–wavelength stimuli at short post–stimulus–onset times. APB combined with PDA produced results similar to aspartate. Spectral sensitivity derived from aspartate–exposed subjects at various post–stimulus–onset times were similar. Conclusions: The initial voltage–negative response of young zebrafish to short–wavelength stimuli appears to be due to photoreceptor activity. ERG waveform differences across stimulus wavelengths suggest that the circuitry of ultraviolet– and short–wavelength cone types is different from that of middle– and long–wavelength cone types in zebrafish.

Keywords: electroretinography: non–clinical • retina: distal (photoreceptors, horizontal cells, bipolar cells) • retinal development