D2-dopamine receptor blockade impairs motion detection in goldfish

Under photopic illumination conditions, motion detection in goldfish is dom inated by the long-wavelength-sensitive cone type (L-cone), and under scoto pic conditions motion it is determined by rods (Schaerer & Neumeyer, 1996). The switch from rod-dominated to cone-dominated motion detection occurs du ring light adaptation. It has been suggested that dopamine acts as a neuron al light-adaptative signal. It is known that dopamine affects wavelength di scrimination through D1-dopamine receptors (Mora-Ferrer & Neumeyer, 1996), and the dorsal light reflex through D1- and D2-dopamine receptors (Lin & Ya zulla, 1994a). The purpose of this study was to determine whether dopamine influenced movement detection by goldfish, and if so, which dopamine recept or was involved. The D2-dopamine receptor antagonist sulpiride reduced the animal's sensitivity to the moving stimulus, whereas SCH 23390, a D1-dopami ne receptor antagonist, did not have any effect. The effect of sulpiride is discussed in relation to known sulpiride effects on retinal neurons and th e retinal pigment epithelium.