DISRUPTION OF THE ACTIVITY-REST CYCLE BY MAOI TREATMENT - DEPENDENCE ON LIGHT AND A SECONDARY VISUAL PATHWAY TO THE CIRCADIAN PACEMAKER

The disruptive effects on the activity-rest cycle of the monoamine oxi dase inhibitor (MAOI) clorgyline and of continuous light were examined in Syrian hamsters, When administered in dim and moderate light inten sities, clorgyline delayed the daily onset of wheel-running. When admi nistered in bright light, it dissociated the circadian rhythm of wheel -running. This dissociation was prevented by lesions of the intergenic ulate leaflet of the ventral lateral geniculate nucleus, Constant dark ness restored the circadian rhythm of wheel-running in hamsters with d isrupted circadian rhythms, The phase of the restored rhythm of wheel- running was shifted 6-12 h later than the phase of wheel-running prior to dissociation, Our results suggest that MAOI treatment weakens the coupling between oscillators that comprise the circadian pacemaker, an d augments the disruptive effects of continuous light acting via the i ntergeniculate leaflet region of the ventral lateral geniculate nucleu s, These effects on the circadian pacemaker may be responsible for dis ruptions of the sleep-wake cycle that occur as side effects when MAOIs are used clinically to treat depression and might play a role in the induction of mania and rapid cycling by antidepressants. Published 199 8 Elsevier Science Inc.