[Electroretinographic study of chromatic vision].

PURPOSE

To describe the electroretinogram of the South-American opossum (Didelphis aurita) obtained by chromatic stimulus of specific wavelengths. The electroretinogram records voltage variations of retinal cells triggered by light stimulation. The electroretinogram represents the combination of electric activity of many different cells and varies according to retinal physiology and examination methods.

METHODS

We recorded the electroretinogram of six animals in dark adaptation using chromatic Kodak Wratten filters, and recorded the spectral sensitivity to specific wavelengths in the spectrum of blue, green, yellow, orange and red light bands.

RESULTS

The most consistent electrorretinographic results were obtained when the animals were stimulated by selective spectral bands instead of white light. These results are consistent with the absorbance curve of the opsins described in marsupial photoreceptors. Previous studies using microspectrophotometry of opsins and retinal immunohistochemistry suggested marsupial trichromacy. This morphologic knowledge has not before been physiologically demonstrated by electroretinographic methods.

CONCLUSION

The South-American opossum has proven to be an interesting experimental animal for comparative visual physiology studies among other mammals, especially studies on phylogenetic of chromatic vision. The opossum represents a retinal model that superimposes both the photopic and scotopic systems; and the Didelphis genus shows few changes when compared to the fossils of the Pleocene period. Therefore the marsupial's visual system retrieves characteristics from ancient mammal evolution to the retinal patterns found in modern mammals.