Duplex Function in the Grey Squirrel's Electroretinogram

Abstract

THE grey squirrel (Sciurus carolinesis leucotis) was initially considered to have an all-cone retina, based on evidence obtained by light microscopy^1,2 and electroretinography². In support of this, a difference spectrum obtained by reflexion densitometry was found to peak at 535 mµ³. Afterwards a difference spectrum of a photopigment extracted from this retina peaked at 504 mµ, however, and resembled rhodopsin⁴. Thereafter a group of diurnal squirrels including the grey squirrel was found to have double-peaked ERG spectral sensitivity curves, suggesting that there was more than one receptor mechanism in these retinæ⁵. Similar ERG results have been reported for other diurnal squirrels^6,7. Recently, conditioning experiments on the grey squirrel demonstrated a peak wave-length sensitivity at 502 mµ (ref. 8), and rod-like in addition to cone receptors were found by electronmicroscopy⁹. This report shows that there are at least two receptor systems contributing to the grey squirrel's ERG which behave similarly to the rod and cone components of the ERGs of duplex retinæ.