VISION IN THE ULTRAVIOLET RANGE IN CARASSIUS AURATUS (OSTARIOPHYSI, CYPRINIFORMES, CYPRINIDAE): AN ELECTROPHYSIOLOGICAL STUDY

Although it is known that the goldfish can discriminate color in the ultraviolet range, to date there is no electrophysiological data to reveal the neural basis of this discrimination. In the present study, intracellular responses to monochromatic stimuli including the UV range were recorded from the outer retina of the goldfish. Recordings were performed on isolated retinas, using borosilicate microelectrodes filled with 3M KCl (100-500MΩ). Each cell was tested with monochromatic stimuli of equal quanta (300-700 nm). The size of the receptive field, as well as the response/intensity function were also assessed in different spectral regions, in order to calculate the spectral sensitivity of the studied cells. A triphasic bipolar cell type with depolarizing responses from 300 to 400 nm and 520 to 700 urn (UV+G+R+/B−) was found. These cells (n=2) also show spacial opponency in their receptive fields, with a typical center/surround organization. This pattern corresponds, from 400 nm on, to that of the already known biphasic colour-coded bipolar cells. The opponency between the ultraviolet and violet spectral regions, however, shows that this cell type is in fact triphasic. This might be the first step in the neural mechanism for discrimination of ultraviolet light.