Light Adaptation of the Late Receptor Potential in the Cat Retina

Abstract

Light adaptation of the vertebrate visual system is, at least in part, a function of the retina. Electrical recordings from various vertebrate retinas have shown that ganglion cells as well as cells of the inner nuclear layer show adaptive properties similar to those of the whole visual system measured psycho-physically (Dowling, 1963; Barlow and Levick, 1969). Two different mechanisms of retinal light adaptation have been described. At high background illuminations photochemical adaptation results from changes in the photopigment concentration in the photoreceptors (Dowling, 1963). In addition, neural adaptation has been demonstrated at background illuminations where no substantial changes in photopigment concentration can be detected (Dowling, 1963). Yet the site and the mechanism of neural adaptation is not fully understood and the role of the photoreceptors in neural adaptation is still controversial. In the rat retina a strong case has been made for the view that the site of neural adaptation is located proximal to the receptors, within the inner nuclear layer (Dowling, 1963). In the rat retina the increment threshold of the a-wave of the electroretinogram, thought to be generated in the rod terminals (Brown, 1968), is only slightly increased by background illuminations which raise the increment threshold of the b-wave by a large amount. The b-wave is generated by cells in the inner nuclear layer. A similar difference has been noted for the effect of light adaptation on the a- and b-waves of the electroretinogram of the cat retina (Arden and Brown, 1965).