Circadian regulation of chick electroretinogram: effects of pinealectomy and exogenous melatonin

Melatonin is an important component of the avian circadian system. This stu dy investigates the effects of pinealectomy (Pin-X) and melatonin implantat ion (Mel) on electroretinogram (ERG) rhythms in chicks. Feeding rhythms wer e monitored to obtain a phase reference for ERG recordings. Pin-X and Mel h ad little or no effect on feeding rhythms. Sham-operated Pin-X and vehicle implantation had no effect on ERG rhythms in the light-dark (LD) cycle or c onstant darkness (DD). ERG a- and b-wave amplitudes were higher during the day than during the night. The a-and b-wave implicit times were shorter dur ing the day than during the night. a-Wave sensitivity was higher during the night than during the day, whereas b-wave sensitivity was not rhythmic. Pi n-X abolished the circadian rhythm of b-wave amplitude and implicit time in DD but had no effect on a-wave rhythmicity. Mel abolished the rhythm of b- wave amplitude and of a-and b-wave implicit time in DD. Neither treatment a ffected ERG in LD. These results suggest that the circadian system regulate s rhythmic visual function in the retina at least partially through Mel. Th e role played by the pineal gland and Mel may be specific to some physiolog ical modalities (e.g., vision) while not influencing others (e.g., feeding) .