[Electroretinographic study of chromatic vision].
OBJECTIVE
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.


CONCLUSIONS
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.
Cunha
Daniela Cavalcanti Ferrara de Almeida
DC
Universidade Federal do Rio de Janeiro, Rua Euzébio Naylor 155, Rio de Janeiro, RJ CEP 22793-770, Brazil. daniela@ferrara.com.be
Hokoç
Jan Nora
JN
Dantas
Adalmir Morterá
AM
Moraes Junior
Haroldo Vieira de
HV
Moraes
Antônio Marcos Mello
AM
D000818:Animals; D005075:Biological Evolution; D003116:Color; D003118:Color Perception / Q000502:physiology*; D003623:Dark Adaptation; D004596:Electroretinography; D005260:Female; D008027:Light; D008297:Male; D008322:Mammals; D008394:Marsupialia / Q000502:physiology*; D023421:Models, Animal; D010775:Photic Stimulation; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology*; D012684:Sensory Thresholds / Q000502:physiology; D014785:Vision, Ocular / Q000502:physiology*