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  • Title: [Variations of hypothalamic and cortical prostaglandins and monoamines reveal transitions in arousal states: microdialysis study in the rat].
    Author: Nicolaidis S, Gerozissis K, Orosco M.
    Journal: Rev Neurol (Paris); 2001 Nov; 157(11 Pt 2):S26-33. PubMed ID: 11924034.
    Abstract:
    Brain microdialysis coupled with EEG recording allowed us to track dynamic neurochemical changes every 3 or 6 minutes in relation to sleep/wake cycles. We chose to investigate prostaglandins (PG) and monoamines (catecholamines, serotonin and metabolites) because of their respective role in the states of vigilance, mainly suggested by pharmacological approaches, and because of the known interactions between PGs and monoamines. We focused on the paraventricular and ventromedial nuclei of the hypothalamus for their involvement in the relationships between feeding, metabolic rate and sleep, and the prefrontal cortex for its role in vigilance. These studies revealed a few changes in prostaglandin or monoamine levels as a function of a given state of vigilance. In particular, serotonin levels were higher during wakefulness than during sleep in both hypothalamus and cortex. Both hypothalamic and cortical PGE2 levels were higher during wakefulness than during slow wave sleep and still higher during paradoxical sleep in the cortex. Cortical PGD2 showed an exactly reverse profile of PGE2. These changes are in agreement with the described awaking action of PGE2 and with the hypnogenic action of PGD2. Our most informative findings were the sequential changes around transitions from one state to another that allow to predict the moment of onset of both sleep and wakefulness. Both in hypothalamus and in cortex, ondulatory patterns of PGE2 were encountered around the transitions between states. PGE2 was high in the middle of wakefulness, then regularly dropped announcing the occurrence of sleep, where the drop persisted before giving place to a rise in prediction to the next period of wakefulness. A similar profile was also observed for cortical serotonin, but its low levels reached a plateau during sleep. Cortical dopamine levels showed sudden and dramatic drops during short periods of wakefulness closely surrounding slow wave sleep. In some instances, as in the case of PGE2, similar profiles of variations could be found both in the hypothalamus and cortex. But in most cases, different and even opposite profiles were encountered in those two structures. Interestingly, in some instances, the pattern of changes in both prostaglandins and monoamines were similar, as for example between hypothalamic PGE2 and dopamine as well as between cortical PGE2 and serotonin. These similarities support the idea of the suggested interaction between prostaglandins and monoamines, in particular concerning their involvement in the regulation of sleep/wake cycles.
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