Influence of histamine receptor agonists and antagonists on ultradian rhythm of EEG in the posterior hypothalamus of the rat

Abstract

The delta and theta frequency bands of the electroencephalogram (EEG) in the posterior hypothalamic area (PH) of rats vary according to an ultradian rhythm with a frequency of approximately 1 cycle/100 min. The influence of histamine-related drugs on the ultradian hypothalamic EEG rhythm was now studied in urethane anaesthetized rats. Injected into the lateral ventricle, metoprine (inhibitor of histamine catabolism) and αuoromethylhistidine (inhibitor of histamine synthesis) did not alter the duration of the rhythmic changes. The H 1 receptor agonist 2-(2-aminoethyl)-thiazole was ineffective, while mepyramine (H 1 receptor antagonist) prolonged the cycle duration of delta and theta frequency bands. Stimulation of H 2 and H 3 receptors by amthamine and immepip, respectively, also prolonged the cycle duration of these frequency bands, while the H 2 antagonist famotidine and the H 3 antagonist thioperamide exerted the opposite effect. Our results indicate that the ultradian EEG rhythm in the PH is susceptible to regulatory influences mediated by the histaminergic system of the brain.