Endogenous circadian rhythm in electroretinogram of free-moving lizards.

An endogenous circadian rhythm in the electroretinogram (ERG) of free-moving lizards, Anolis carolinensis, can be demonstrated in experiments lasting up to eight days. The rhythm does not appear to arise from processes that could modulate the amount of light reaching the photoreceptors. Moreover, since the rhythm is well-developed in the b-wave, but not a-wave, the direct modulation of neural processes proximal to the photoreceptors may be involved. Lastly, this rhythm may have ecological significance for this diurnally active species, since the largest responses occur at projected midday.