VISUAL PIGMENTS AND OIL DROPLETS FROM 6 CLASSES OF PHOTORECEPTOR IN THE RETINAS OF BIRDS

Microspectrophotometric examination of the retinal photoreceptors of t he budgerigar (shell parakeet), Melopsittacus undulatus (Psittaciforme s) and the zebra finch, Taeniopygia guttata (Passeriformes), demonstra te the presence of four, spectrally distinct classes of single cone th at contain visual pigments absorbing maximally at about 565, 507, 430- 445 and 360-380 mn, The three longer-wave cone classes contain coloure d oil droplets acting as long pass filters with cut-offs at about 570, 500-520 and 445 mm, respectively, whereas the ultravioiet-sensitive c ones contain a transparent droplet, The two species possess double con es in which both members contain the long-wave-sensitive visual pigmen t, but only the principal member contains an oil droplet, with cut-off at about 420 MI, A survey of the cones of the pigeon, Columba livia ( Columbiformes), confirms the presence of the three longer-wave classes of single cone, but also reveals the presence of a fourth class conta ining a visual pigment with maximum absorbance at about 409 nm, combin ed with a transparent droplet, No evidence was found for a fifth, ultr aviolet-sensitive receptor. In the chicken, Gallus gallus (Galliformes ), the cone class with a transparent droplet contains ''chicken violet '' with maximum absorbance at about 418 mn, The rods of all four speci es contain visual pigments that are spectrally similar, with maximum a bsorbance between about 506 and 509 nm, Noticeably, in any given speci es, the maximum absorbance of the rods is spectrally very similar to t he maximum absorbance of the middle-wavelength-sensitive cone pigments . (C) 1997 Elsevier Science Ltd.