title: Acute and long-term effects of the 5-HT2 receptor antagonist ritanserin on EEG power spectra, motor activity, and sleep: changes at the light-dark phase shift.
abstract: Parallel effects of a single injection of the 5-HT(2) receptor antagonist ritanserin on EEG power spectra, sleep and motor activity were measured for a 20-h period in freely moving Sprague-Dawley rats. Ritanserin (0.3 mg/kg, i.p.), administered at light onset (passive phase), caused an immediate transient increase in the EEG power density in the low frequency range (0.25-6 Hz, mainly delta activity) and a depression in the high frequency range (27-30 Hz) accompanied by a decrease in vigilance and light slow wave sleep (SWS-1), intermediate stage of sleep and increase in deep slow wave sleep (SWS-2) compared to control treatment. All these effects were over 8 h after the injection. Twelve hours after the injection, at dark onset (active phase), there was a marked increase in vigilance and motor activity and decrease in SWS-1 and spindle frequency activity in the control animals, but all these changes were diminished by ritanserin treatment. These effects resulted in a significant relative increase in the intermediate band (peak: 12-15 Hz) of the EEG power spectra and thus, a relative increase in thalamo-cortical synchronization caused by ritanserin at dark onset. Because ritanserin is a selective 5-HT(2) receptor antagonist, we conclude that under physiological conditions serotonin increases EEG desynchronization and produces an increase in vigilance level and motor activity by tonic activation of 5-HT(2) receptors. This regulatory mechanism plays an important role in the waking process, and the appearances of its effects in the light and dark phase are markedly different.
authors.affiliation: Laboratory of Neurochemistry and Experimental Medicine, Department of Neurology, Faculty of Health Sciences, Semmelweis University, National Institute of Psychiatry and Neurology, Huvosvolgyi ut 116, H-1021 Budapest, Hungary.
authors.forename: Sandor
authors.initials: S
authors.lastname: Kantor
authors.forename: Rita
authors.initials: R
authors.lastname: Jakus
authors.forename: Robert
authors.initials: R
authors.lastname: Bodizs
authors.forename: Peter
authors.initials: P
authors.lastname: Halasz
authors.forename: Gyorgy
authors.initials: G
authors.lastname: Bagdy
mesh_terms: D000818:Animals; D002940:Circadian Rhythm / Q000187:drug effects* / Q000502:physiology; D003624:Darkness; D004569:Electroencephalography / Q000187:drug effects*; D008297:Male; D009043:Motor Activity / Q000187:drug effects* / Q000502:physiology; D017440:Photoperiod; D051381:Rats; D017207:Rats, Sprague-Dawley; D011985:Receptors, Serotonin / Q000502:physiology*; D016713:Ritanserin / Q000494:pharmacology*; D012702:Serotonin Antagonists / Q000494:pharmacology*; D012890:Sleep / Q000187:drug effects* / Q000502:physiology
chemical_list: D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D016713:Ritanserin