title: Effects of dopamine D1receptor blockade on the ERG b- and d-waves during blockade of ionotropic GABA receptors.
abstract: BACKGROUND
  Some data indicate that the dopaminergic and GABAergic systems interact in the vertebrate retina, but the type of interactions is not well understood.
  
  
  METHODS
  In this study we investigated the effect of dopamine D1receptor blockade by 75 μM SCH 23390 on the electroretinographic ON (b-wave) and OFF (d-wave) responses in intact frog eyecup preparations and in eyecups where the ionotropic GABA receptors were blocked by 50 μM picrotoxin. Student'st-test, One-way repeated measures ANOVA with Bonferroni post-hoc test and Two-way ANOVA were used for statistical evaluation of the data.
  
  
  RESULTS
  We found that SCH 23390 alone significantly enhanced the amplitude of the b- and d-waves without altering their latency. The effect developed rapidly and was fully expressed within 8-11 min after the blocker application. Picrotoxin alone also markedly enhanced the amplitude of the ERG ON and OFF responses and increased their latency significantly. The effect was fully expressed within 25-27 min after picrotoxin application and remained very stable in the next 20 min. The effects of SCH 23390 and picrotoxin are similar to that reported in our previous studies. When SCH 23390 was applied on the background of the fully developed picrotoxin effect, it diminished the amplitude of the b- and d-waves in comparison to the corresponding values obtained during application of picrotoxin alone.
  
  
  CONCLUSIONS
  Our results demonstrate that the enhancing effect of D1receptor blockade on the amplitude of the ERG b- and d-waves is not evident during the ionotropic GABA receptor blockade, indicating an interaction between these neurotransmitter systems in the frog retina. We propose that the inhibitory effect of endogenous dopamine mediated by D1receptors on the ERG ON and OFF responses in the frog retina may be due to the dopamine-evoked GABA release.
authors.affiliation: Department of Physiology, Medical University of Sofia, Sofia, Bulgaria.
authors.forename: Elka
authors.identifier: 0000-0002-3744-7696
authors.initials: E
authors.lastname: Popova
authors.affiliation: Department of Physiology, Medical University of Sofia, Sofia, Bulgaria.
authors.forename: Momchil
authors.initials: M
authors.lastname: Kostov
authors.affiliation: Department of Physiology, Medical University of Sofia, Sofia, Bulgaria.
authors.forename: Petia
authors.initials: P
authors.lastname: Kupenova
keywords: D1 receptors; Dopamine; Electroretinogram; GABA; b-wave; d-wave