Difference between the effects of steady illumination vs. darkness on circadian changes in the processing of visual information in rabbits

Publisher Website
Google Scholar
Abstract
Eight rabbits were synchronized by LD [light dark] 14:10 (200-250: 0 lx). After more than 4 wk of exposure to this zeitgeber 2 types of experiment were performed on each specimen. In type I experiments the electroretinograms (ERG) and visually evoked potentials in response to 3 .mu.s flashes were recorded during the day-time-potential phase of the circadian rhythm, at 1st during steady illumination at either 1200 or 2500 lx and thereupon in darkness, and also during the night-time-potential NTP phase, but then firstly in darkness and afterwards during illumination with the same intensity. In type II experiments the responses to the same flashes were, again, recorded in both phases but now the sequence of illumination, at identical level, and darkness was reversed. It appeared that programed changes in photic responses occurred both in darkness (in type I experiments) and during steady illumination (in experiments of the other type) but that the circadian change in amplitude of the ERG b waves was larger for the ERG recorded in darkness than for those obtained during illumination. It further appeared that the suppressive influence exerted by background illumination on the ERG is stronger during the NTP-phase of the rhythm than in the other phase. The possible roles of this circadian rhythm in retinal photosensitivity for the daily survival of rabbits, and in the origin of photoperiodic changes, are discussed.