Circadian rhythm in the visual system of the lizard Anolis carolinensis.

The electroretinogram (ERG) was recorded from free-moving Anolis lizards once per hour for 5 days. As in our previous work, the b-wave, but not the a-wave, showed a reliable circadian rhythm (CR) in amplitude, with an acrophase near projected noon. Both the a- and b-waves showed a CR in peak time (implicit time, or IT), with the a-wave IT being longest near midnight, and the b-wave IT at midday. Acrophases were shifted when animals were housed on a phase-shifted light-dark cycle. The ERG CR was unaffected by removal of the parietal organ, but it was virtually abolished by removal of the pineal gland, thus suggesting that pineal output (probably melatonin) modulates retinal responses. In addition to the ERG, the tectal light-evoked potential exhibited a CR--a finding compatible with a circadian variation in retinal output. Lastly, the amplitude of the ERG component waveforms showed a seasonal variation, but the ERG CR was constant across the year.