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  • Author or Editor: T. Hajnik x
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Authors: Attila Toth, B. Balatoni, T. Hajnik and L. Detari

Orexin A and orexin B are neuropeptides produced by a group of neurons located in the lateral hypothalamus which send widespread projections virtually to the whole neuraxis. Several studies indicated that orexins play a crucial role in the sleep-wake regulation and in the pathomechanism of the sleep disorder narcolepsy. As no data are available related to the EEG effects of orexin A in healthy, freely moving rats, the aim of the present experiments was to analyze EEG power changes in the generally used frequency bands after intracerebroventricular orexin A administration.Orexin A administration (0.84 and 2.8 nM/rat) differently affected fronto-occipital EEG waves in the different frequency bands recorded for 24 hours. Delta (1–4 Hz) and alpha (10–16 Hz) power decreased, while theta (4–10 Hz) and beta (16–48 Hz) power increased. Decrease of the delta power was followed by a rebound in case of the higher orexin A dose. This complex picture might be explained by the activation of several systems by the orexin A administration. Among these systems, cortical and thalamic circuits as well as the role of the neurons containing corticotrophin-releasing factor might be of significant importance.

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Sleep is homeostatically regulated suggesting a restorative function. Sleep deprivation is compensated by an increase in length and intensity of sleep. In this study, suppression of sleep was induced pharmacologically by drugs related to different arousal systems. All drugs caused non-rapid eye movement (NREM) sleep loss followed by different compensatory processes. Apomorphine caused a strong suppression of sleep followed by an intense recovery. In the case of fluoxetine and eserine, recovery of NREM sleep was completed by the end of the light phase due to the biphasic pattern demonstrated for these drugs first in the present experiments. Yohimbine caused a long-lasting suppression of NREM sleep, indicating that either the noradrenergic system has the utmost strength among the examined systems, or that restorative functions occurring normally during NREM sleep were not blocked. Arousal systems are involved in the regulation of various wakefulness-related functions, such as locomotion and food intake. Therefore, it can be hypothesized that activation of the different systems results in qualitatively different waking states which might affect subsequent sleep differently. These differences might give some insight into the homeostatic function of sleep in which the dopaminergic and noradrenergic systems may play a more important role than previously suggested.

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