The pathway responsible for EEG synchronization and effect of histamine on this system

Electrical stimulation (3 Hz, 0.5 volts) to the midbrain reticular formation of conscious rats induced significant increase of EEG power densities (synchronization) recorded at the frontal cortex (FCOR), nucleus ventralis thalami (VE), or nucleus medialis centralis thalami (CM). Significant synchronization was also observed in the FCOR when electrical stimulation was applied to the VE and CM. When ipsilateral and bilateral VEs were electrocoagulated, no EEG synchronization was observed in the FCOR and CM. Intracerebroventricular administration of histamine (Hi) caused a marked suppression of FCOR EEG synchronization in both CM-lesioned and normal rats through H1 receptors. EEG synchronization in FCOR was not induced in ipsilateral or bilateral VE-lesioned rats after RF stimulation. When Hi (1 microgram) was injected into the VE of normal rats, EEG synchronization of FCOR was markedly reduced after RF or VE stimulation. No such changes were induced when Hi was injected into the CM.