title: [Electroretinographic study of chromatic vision].
abstract: 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.
authors.affiliation: Universidade Federal do Rio de Janeiro, Rua Euzébio Naylor 155, Rio de Janeiro, RJ CEP 22793-770, Brazil. daniela@ferrara.com.be
authors.forename: Daniela Cavalcanti Ferrara de Almeida
authors.initials: DC
authors.lastname: Cunha
authors.forename: Jan Nora
authors.initials: JN
authors.lastname: Hokoç
authors.forename: Adalmir Morterá
authors.initials: AM
authors.lastname: Dantas
authors.forename: Haroldo Vieira de
authors.initials: HV
authors.lastname: Moraes Junior
authors.forename: Antônio Marcos Mello
authors.initials: AM
authors.lastname: Moraes
mesh_terms: 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*