Abstract
The effects of dopamine D2-class receptor blockade by sulpiride on the electroretinographic (ERG) b-wave (ON response) and d-wave (OFF response) were investigated in light-adapted turtle (Trachemys scripta elegans) and frog (Rana ridibunda) eyecups. For turtle ERG, sulpiride (240 μM) produced an amplitude increase of the b- and d-waves, while the 40 μM and 120 μM of sulpiride were ineffective. Alternatively, for frog ERG, a well-developed and dose-dependent b- and d-wave amplitude decrease was obtained with 40 μM and 240 μM sulpiride. In both species, 240 μM sulpiride significantly affected the maximal voltage range of the ERG responses without altering their relative sensitivity (determined by the semi-saturation point). The absolute sensitivity of the ON and OFF responses (evaluated by threshold estimation) was not significantly altered for turtle ERG, but it was decreased for frog ERG. The time characteristics of the ERG responses were unchanged in both species. Our results show important differences between dopamine D2-class receptor-mediated pathways in turtle and frog retina (revealed by ERG).
Highlights
IntroductionAll vertebrate species have retinal dopa‐ minergic neurons identified as amacrine and/or inter‐ plexiform cells (for reviews: Popova 2014a, Witkovsky 2004)
Dopamine is the major catecholamine in the verte‐ brate retina
The b‐ and d‐wave amplitudes obtained during the blocker application did not differ significantly from the corresponding val‐ ues obtained in control experiments (Fig. 1A, B)
Summary
All vertebrate species have retinal dopa‐ minergic neurons identified as amacrine and/or inter‐ plexiform cells (for reviews: Popova 2014a, Witkovsky 2004). Dopamine released by these neurons can act on two classes of dopamine receptors: D1‐class (including D1 and D5 type) and D2‐class (including D2, D3 and D4 type). The significance of dopamine action, mediated by D1‐ or D2‐class re‐ ceptors, for global retinal function can be revealed by investigating changes of the electroretinogram (ERG) during manipulation of the two receptor classes. We demonstrated that combined D1 and D2 receptor block‐
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