title: Alouatta trichromatic color vision: cone spectra and physiological responses studied with microspectrophotometry and single unit retinal electrophysiology.
abstract: The howler monkeys (Alouatta sp.) are the only New World primates to exhibit routine trichromacy. Both males and females have three cone photopigments. However, in contrast to Old World monkeys, Alouatta has a locus control region upstream of each opsin gene on the X-chromosome and this might influence the retinal organization underlying its color vision. Post-mortem microspectrophotometry (MSP) was performed on the retinae of two male Alouatta to obtain rod and cone spectral sensitivities. The MSP data were consistent with only a single opsin being expressed in each cone and electrophysiological data were consistent with this primate expressing full trichromacy. To study the physiological organization of the retina underlying Alouatta trichromacy, we recorded from retinal ganglion cells of the same animals used for MSP measurements with a variety of achromatic and chromatic stimulus protocols. We found MC cells and PC cells in the Alouatta retina with similar properties to those previously found in the retina of other trichromatic primates. MC cells showed strong phasic responses to luminance changes and little response to chromatic pulses. PC cells showed strong tonic response to chromatic changes and small tonic response to luminance changes. Responses to other stimulus protocols (flicker photometry; changing the relative phase of red and green modulated lights; temporal modulation transfer functions) were also similar to those recorded in other trichromatic primates. MC cells also showed a pronounced frequency double response to chromatic modulation, and with luminance modulation response saturation accompanied by a phase advance between 10-20 Hz, characteristic of a contrast gain mechanism. This indicates a very similar retinal organization to Old-World monkeys. Cone-specific opsin expression in the presence of a locus control region for each opsin may call into question the hypothesis that this region exclusively controls opsin expression.
authors.affiliation: Instituto de Ciências Biológicas, Universidade Federal do Pará, Belém, Pará, Brazil; Núcleo de Medicina Tropical, Universidade Federal do Pará, Belém, Pará, Brazil.
authors.forename: Luiz Carlos L
authors.initials: LC
authors.lastname: Silveira
authors.affiliation: Instituto de Ciências Biológicas, Universidade Federal do Pará, Belém, Pará, Brazil.
authors.forename: Cézar A
authors.initials: CA
authors.lastname: Saito
authors.affiliation: Instituto de Ciências Biológicas, Universidade Federal do Pará, Belém, Pará, Brazil.
authors.forename: Manoel
authors.initials: M
authors.lastname: da Silva Filho
authors.affiliation: Department of Ophthalmology, University Hospital Erlangen, Erlangen, Germany.
authors.forename: Jan
authors.initials: J
authors.lastname: Kremers
authors.affiliation: Division of Visual Science, Institute of Ophthalmology, University College London, London, England, United Kingdom.
authors.forename: James K
authors.initials: JK
authors.lastname: Bowmaker
authors.affiliation: State College of Optometry, State University of New York, New York, New York, United States of America; Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.
authors.forename: Barry B
authors.initials: BB
authors.lastname: Lee
mesh_terms: D000508:Alouatta; D000818:Animals; D003116:Color; D003118:Color Perception / Q000235:genetics / Q000502:physiology*; D055253:Color Vision / Q000235:genetics / Q000502:physiology*; D004594:Electrophysiology / Q000379:methods; D005260:Female; D008027:Light; D008297:Male; D015591:Microspectrophotometry / Q000379:methods; D009474:Neurons / Q000502:physiology; D055355:Opsins / Q000235:genetics / Q000502:physiology; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology*; D012165:Retinal Ganglion Cells / Q000378:metabolism / Q000502:physiology; D012168:Retinal Pigments / Q000235:genetics / Q000502:physiology*; D014785:Vision, Ocular / Q000235:genetics / Q000502:physiology
chemical_list: D055355:Opsins; D012168:Retinal Pigments