Spatial distribution of visual pigment and dopamine in the bullfrog retina

Visual pigments and a neurotransmitter, dopamine, were quantitatively investigated in the retina of adult bullfrog, Rana catesbeiana. The adult bullfrog (body length 15-16 cm, body weight 375 +/- 52 g, n = 10) had 21.4 +/- 4.2 nmol visual pigment and 209 +/- 28 pmol dopamine in retinal areas of 266 +/- 27 mm2. Greater pigment densities were recorded in a semicircular band around the optic disc, extending to the nasal and temporal peripheries of the ventral retina. The area with the highest concentration of visual pigment was found in the middle of the dorsal retina, 3-4 mm dorsal to the optic disc. A high concentration of vitamin A2-based pigment was found in the dorsal quarter of the retina (porphyropsin zone); the zone extended up to the most ventral part along peripheral regions of the retina. There was also a band with higher dopamine concentrations although it was not so prominent as that of the visual pigment; the highest concentration of dopamine was found in the area immediately dorsotemporal to the optic disc. Fluorescence micrography indicated that the distribution pattern of catecholamine-containing amacrine cells paralleled that of the dopamine content. The topographic map of dopamine was slightly different from that of visual pigment in the bullfrog retina.