Chronic clorgyline treatment of Syrian hamsters: an analysis of effects on the circadian pacemaker.

Clorgyline, a type A monoamine oxidase inhibitor with antidepressant properties when administered to depressed patients, is often associated with disturbances of the human sleep-wake cycle. In order to assess its effects on the mammalian circadian system, this drug was administered chronically to Syrian hamsters. It was found to affect the hamster circadian system in four specific ways. Clorgyline increased the intrinsic period of wheel-running activity, altered the phase response curve to brief light pulses, altered the reduced waveform of running activity in animals maintained in light-dark cycles or constant darkness, and increased the activity-rest ratio in animals maintained in constant darkness. Our data support the interpretation that clorgyline exhibits direct or indirect input to the circadian pacemaker and alters the processing of photic information to the pacemaker.