Light adaptation in mouse cones

Abstract

The rod photoreceptors are used for twilight vision and are saturated in daylight. Cones function in daylight and have not been found to saturate at any intensity available. Both rods and cones have the ability to regulate their operation as a function of the background illumination so as to extend their operational functioning range. General light adaptation manifestations can be observed as photoreceptor desensitization and photoresponse acceleration. In this study the function of cone light adaptation was studied.

The electrophysiological changes in mouse cones caused by light adaptation were recorded as mass potential electroretinograms (ERG). The photoreceptor's response to light was pharmacologically isolated. In one case, the retinae were subjected to short stepped backgrounds (test flash applied 2 s after background onset) and in the othe case continuous backgrounds (test flash applied more than 2 min. after background onset). Characteristics of mouse cone light adaptation include retardation in time to maximum (tp) in both types of backgrounds. The sensitivity drop in the photoreceptors when subjected to increasingly stronger stepped background illumination was smaller than in the continuous background. The results obtained in these experimental conditions indicate that light adaptation functions differently in mouse cones compared to other species.

Additionally, a mouse lacking functional rod phototransduction, due to targeted deletion of α transducin gene (Trα – / – ), was investigated in order to determine whether the Trα – / – mouse could be used as a model for cone phototransduction experiments. The photoresponse kinetics of the Trα – / – photoreceptors, though, were significantly retarded. Furthermore, the Trα – / – photoreceptors were somewhat more light sensitive than WT mouse cones, and highly more sensitive to adapting background illumination.