Does the Ventromedial Hypothalamic Nucleus Contain a Self-sustained Circadian Oscillator Associated with Periodic Feedings?

Multiple unit activities (MUAs) of the ventromedial hypothalamic nucleus (VMH) were recorded from intact free-moving male rats. Rhythmic activities observed in the VMH were not distinguishable from those recorded in other places of the brain. When exposed to restricted daily feeding schedules, animals with suprachiasmatic nucleus (SCN) lesions developed a rhythm in motor activity and a rhythm of the VMH with a peak of activity immediately after and a trough right before the feeding. While neural activities of the SCN revealed circadian rhythms even after a lesion of the VMH, circadian rhythms in MUA of the VMH were completely abolished by a lesion of the SCN. Although the VMH is involved in the synchronization of rhythms to periodic feeding, the present results indicate that, unlike the SCN which contains an oscillator associated with light, the VMH does not contain another self-sustained oscillator associated with food.