Functional Characteristics of Juvenile Lamprey Photoreceptors

The visual system of freshwater vertebrates shifts photoreceptor sensitivity to longer wavelengths and extends visual sensitivity beyond the range of human vision. One mechanism of enhancing sensitivity to long-wavelength light is to replace the 11-cis retinal chromophore in photopigments with 11-cis 3,4-didehydroretinal. Migratory species of amphibians and salmon can dynamically tune their visual system by altering the balance of 11-cis retinal and 11-cis 3,4-didehydroretinal. Here it is shown that the same process is available in sea lampreys. The ratio of vitamin A2-to-A1 increases as the animals migrate from the open ocean into inland freshwater environments. Suction-electrode recording was used to measure the spectral sensitivity in both adult and juvenile Petromyzon marinus. Primarily, these data show that juvenile lamprey possess a duplex retina. Secondarily, these data demonstrate a strong correlation between the red-shifted light environment of freshwater habitats and the use of the red-shifted vitamin A2 in this primitive vertebrate