Spectral mechanisms in the retina of the Arctic ground squirrel.

Abstract

The electroretinogram (ERG) was used to investigate the spectral mechanisms present in the retina of the Arctic ground squirrel (Spermophilus undulatus). Under conditions of dark adaptation, the spectral sensitivity of this eye is adequately accounted for by the operation of a typical mammalian rhodopsin (500-nm peak) indicating that, like other ground squirrel species, the Arctic ground squirrel eye probably contains a population of functional rods. When the eye was adapted to lights having a luminance of 0.1 cd/m2 or greater, spectral sensitivity shifted to a new peak location of about 520 nm. Experiments involving chromatic adaptation led to the conclusion that there are at least two spectral mechanisms in this retina which are operative at photopic light levels. These results, along with measurements of preretinal absorbance, indicate that the spectral mechanisms in the retina of the Arctic ground squirrel are very similar to those previously described for several other species of ground-dwelling sciurids.