The Involvement of the Intergeniculate Leaflet in the Potentiation of Photic Phase Shifts by the 5-HT1A Mixed Agonist/Antagonist BMY 7378

Abstract

The suprachiasmatic nucleus (SCN) is the master circadian pacemaker. Photic stimuli conveyed by fibers innervating the SCN can synchronize the master clock with the environment. The serotonin (5-HT) 1A mixed agonist/antagonist BMY 7378 can enhance the magnitude of these changes, which could help realign the circadian rhythms of individuals whose rhythms have become desynchronized. Direct administration of BMY 7378 to the SCN is not sufficient to enhance phase shift to light. The intergeniculate leaflet (IGL) like the SCN receives both direct retinal input and serotonergic innervation; therefore BMY 7378 may be exerting its influence through the IGL. Radio frequency lesion of the IGL and neurotoxic lesion of the 5-HT fibers innervating the IGL both result in phase shift to light which are not significantly larger than controls, indicating that both are necessary for BMY 7378 to potentiate photic phase shifts.