Visual pigments of the tree shrew ( Tupaia belangeri) and greater galago ( Galago crassicaudatus): A microspectrophotometric investigation

Abstract

Optical density, linear dichroism and bleaching difference spectra were measured in photoreceptors from the cone-dominated retina of the tree shrew ( Tupaia belangeri) and from the rod-dominated retina of the greater galago ( Galago crassicaudatus) using a single-beam, wavelength-scanning, dichroic microspectrophotometer. In Tupaia, we obtained spectral records from 272 cone receptors (from 10 eyes), of which 264 were long-wave sensitive ( λ max = 555 ± 6 nm) and 8 were short-wave sensitive ( λ max = 428 ± 15 nm). Also, one anatomically-recognizable rod receptor was encountered and showed a peak absorption at approx. 496 nm. No mid-wave sensitive cone pigment was found, as would be expected in deutan-type dichromats like the tree shrew. Pre-retinal absorption by the cornea and lens was maximal at 370 nm and negligible beyond 430 nm. In Galago, all outer segments measured were rod-like in appearance ( λ max near 501 nm). Measurements of pre-retinal absorption yielded a single-peaked function with a maximum at 363 nm.