Ultra-violet and blue induced migration of screening pigment in the retina of the mothDeilephila elpenor

Abstract

1. The present study concerns the migration of the screening pigment in the compound eye of the mothDeilephila elpenor and its relation to the activity of the visual cells. Movements of the screening pigment were determined by microphotometric measurement, and the electroretinogram (ERG) was used as an index of retinal activity. 2. A light stimulus caused a reflectance change that proceeded in three phases: an initial increase in reflectance, followed by a decrease and a final slow increase. The amplitude of the decrease, i.e. of the pigment dispersion, was found to be determined by the total number of light quanta incident on the eye. The reflectance decrease could be approximated by a first order photochemical reaction with a maximal summation time of at least 80 s. 3. The spectral efficiency of the reflectance change between 338 and 530 nm differed from the spectral efficiency of the dark adapted retina recorded electrophysiologically, but was similar to the efficiency recorded during selective light adaptation of the green sensitive visual cells. Highest sensitivity was recorded in response to UV stimuli. Correspondingly, there was no distinct correlation between the amplitude of the ERG and the amplitude of the simultaneously recorded decrease in reflectance after UV, blue-violet or green light. The green stimulus elicited the largest ERG response but the smallest pigment dispersion. These results indicate that the contribution of the green sensitive visual cells to the pigment dispersion is small. 4. The screening pigment was observed by transmission microscopy in preparations consisting of only the screening pigment cells, dioptric structures, and small visual cell rests kept in a depolarizing, high extracellular potassium concentration. UV and blue-violet light stimuli induced pigment dispersion similar to that observed in intact eyes. The result suggests that photosensitive pigment(s) are located in some element outside the visual cells, but does not preclude that the visual cells participate in the normal regulation of pigment dispersion.