Aging Affects the Ocular Circadian Pacemaker of Aplysia californica

The eye of Aplysia has been used to explore various aspects of circadian rhythms. The authors discovered that age has profound effects on the circadian rhythm of nerve impulses from the eye. With age, there was a significant decrease in the amplitude of the rhythm. The decrease appeared to be continuous over the life span of the animal and was observed both in vitro and in vivo. The free-running period and phase angle of the rhythm steadily increased with age, indicating that the pacemaker itself was affected by age. Rates of transcription and translation were significantly increased with age, suggesting that age-associated alterations of the pacemaker may occur through changes in macromolecular synthesis. Interestingly, eyes from some older (≥10 months) animals had “cloudy” lenses (cataracts). Highly damped or arrhythmic rhythms always were seen in eyes with cloudy lenses. Morphology of eyes with cloudy lenses indicated severe retinal degeneration. No such degeneration was observed in eyes with clear lenses that were used in the analysis of the rhythm with age.