Abstract
Abstract: :
Purpose: Temporal resolution in goldfish is modulated by dopamine through a D2-R mechanism as demonstrated in behavioural experiments (Mora-Ferrer & Gangluff, in press). However, little is known about the localization and function of D2-R in fish retina. The effect of specific D1- and D2-R antagonists on temporal transfer properties (TTP) of the goldfish retina was investigated using the ERG. Methods: Photopic ERG were measured in the vitreous and at various retinal depths before and after intravitreal injection of sulpiride, SCH 23390 or aspartate. Aspartate was used to determine potential effects of either of the dopamine receptor antagonists on photo receptor TTP. Drug concentrations of sulpiride and SCH 23390 as well as the experimental procedure were similar to the ones used in the behavioural experiments. Stimuli were a flickering light (2-50 Hz) for the overall TTP and single light-pulses (100 ms) for intra-retinal ERG measurements. Results: The amplitude-frequency plot of the ERG prior injection shows a low pass characteristic with an upper corner frequency w around 25 Hz. After injection of sulpiride w shifted by about 25-30% to lower frequencies whereas SCH 23390 had no effect. Nevertheless, both sulpiride and SCH 23390 changed the single pulse response properties at all retinal depths recorded. Isolated photo receptor response was not altered by sulpiride. Conclusions: Sulpiride changed retinal TTP (see figure). The isolated a-wave was not affected by sulpiride. Single-pulse measurements at different retinal depths revealed that both D1-and D2-R antagonists substantially altered response properties. SCH 23390 had its largest effects in the ganglion cell layer, but did not change the overall TTP. The effect of sulpiride was largest, for single-pulses, in the inner retina especially on the OFF-part of the ERG. The ERG data for the overall TTP and from single-pulse experiments indicate a D2-R modulated mechanisms involved in temporal coding mainly in the inner retina and exclude D1-R from taking a major part in the modulation of temporal coding.
Keywords: electrophysiology: non-clinical • dopamine • temporal vision