Influence of mediobasal hypothalamic lesion and catecholamine receptor antagonists on ultradian rhythm of EEG in the posterior hypothalamus of the rat.

The delta and theta frequency bands of the EEG in the posterior hypothalamic area (PH) of the urethane-anaesthetized rat vary according to an ultradian rhythm with a frequency of approximately one cycle per 100 min. Injected into the lateral ventricle, prazosin (150 nmol) abolished the rhythmic changes, propranolol (150 nmol) increased, while yohimbine, SKF-83566 and sulpiride (150 nmol each) decreased the cycle duration. Electrocoagulation of the rostral arcuate nucleus and median eminence (Arc-ME) of medial basal hypothalamus abolished the rhythmic EEG changes in the PH. Our results indicate that the ultradian EEG rhythm in the PH is susceptible to regulatory influences mediated by noradrenergic and dopaminergic neurons. For the generation of the ultradian rhythm, the functional integrity of the Arc-ME is required.