Independence of sleep EEG responses to GABAergic hypnotics: biological implications

GABAergic hypnotics are known to depress non-rapid eye movement delta and r apid eye movements and to stimulate non-rapid eye movement sigma (spindles) and beta EEG. This study addressed the question of whether the magnitudes of these effects are significantly correlated. Data were from a study in 16 normal subjects whose sleep was recorded for five nights under placebo and for three nights each under zolpidem (10 mg), triazolam (0.25 mg) and tema zepam (30 mg). EEG was analyzed with both period-amplitude and power spectr al (FFT) analysis. The magnitudes of the EEG and eye movement density respo nses were not significantly correlated for any of the three drugs. It is th erefore unlikely that sleep responses to GABAergic drugs can be explained b y the common cellular action (increased chloride conductance) of these drug s. We suggest that the sleep EEG responses are manifestations of complex (b ut consistent) interactions of excitation and inhibition in large brain sys tems although certain aspects of these responses (e.g. the different time c ourses of delta vs sigma and eye movement responses) may reflect molecular adaptations. A separate observation in this study was the strong traitlike characteristics of the sleep variables studied. These variables were highly correlated across nights of baseline sleep; in addition, individual differ ences in baseline sleep were significantly retained on the third night of t emazepam administration. (C) 2000 Elsevier Science Ltd. All rights reserved .