Chronic clorgyline dampens rat retinal rhythms

In the rat retina, the rhythm of disk-shedding from visual cell outer segments is circadian in nature, whereas autophagic degradation of organelles in inner segments follows a circadian rhythm that persist in constant light but not in constant darkness. The monoamineoxidase inhibitor clorgyline can phase delay circadian rhythms in hamster and rat. However, clorgyline does not phase delay the plasma corticosterone rhythm nor does it delay the phase position of the retinal disk-shedding rhythm in a light-dark cycle or in constant darkness: only the amplitude of the circadian rhythm is reduced. A marked reduction in rhythm amplitude is also found in the number of autophagic vacuoles after chronic clorgyline treatment. Thus the circadian rhythm of disk-shedding appears to be primarily driven by an oscillator within the eye, and clorgyline modulates the light response of retinal parameters but not their timing.