Power spectral electroencephalogram analysis of the effects of ritanserin in freely moving rats during quiet waking.

Changes in the spectral characteristics of the Fast Fourier Transformed (FFT) electroencephalogram (EEG) recorded from the frontal cortex of freely moving rats during quiet waking were studied after blockade of the 5-hydroxytryptamine-2 (5-HT2) receptors by the potent and long acting 5-HT2 antagonist ritanserin administered intraperitoneally (i.p.) at two doses (0.63 and 2.5 mg/kg). The rationale of this approach was to evaluate the subtle ritanserin-induced changes in the EEG in the frequency domain, and thus obtain more information about the neurophysiological effects mediated by brain 5-HT2 receptors and about the mechanisms underlying ritanserin's ability to increase sleep at the expense of wakefulness. Ritanserin induced significant changes in the power spectrum of EEG recorded from the frontal cortex. The activation index (the ratio of the dominant frequency in the power spectrum to the total power) significantly decreased after ritanserin, which was due to the increased EEG power in all frequency bands (except for beta 2) and to the decreased dominant frequency in the EEG spectrum, suggesting ritanserin-reduced EEG activation during quiet waking. The results favor the view of the excitatory modulating action of serotonin mediated via cortical 5-HT2 receptors and suggest that ritanserin could cause a faster transition from waking to sleep.