Ghrelin is an endogenous ligand of the growth hormone secretagogue receptor produced peripherally and centrally. A growing number of studies in mice and rats shows that administration of ghrelin improves several memory processes [3]
[4]
[5]
[7]. However, also an impairment of memory retention in neonatal chicks after ghrelin administration has been reported [6]. In their recent paper, Atcha and colleagues [2] report that ghrelin receptor agonists enhance memory retention in rats. In line with other authors (e. g., [18]), they propose the central ghrelin receptor as a new drug target for therapeutic approaches to treat diseases affecting cognition.
Administration of ghrelin also interacts with sleep regulation. While ghrelin promotes non-rapid eye movement sleep in human males [11]
[12]
[21] and in mice [13], it suppresses sleep in rats [16]
[17]. Sleep, on the other hand, has been shown to enhance nocturnal plasma ghrelin levels [10] and to play a crucial role in memory consolidation [15]. It is discussed to what extent several hormones might play a key role in this process [19]. Especially off-line gains in newly acquired sequential motor skills seem to be exclusively bound to sleep [15], a process in which the hippocampus has been shown to be involved [1]. Despite these reciprocal interactions between memory, ghrelin and sleep, no studies about the effects of ghrelin administration on sleep-associated memory consolidation exist so far. We therefore studied if nocturnal pulsatile ghrelin administration influences the consolidation of a motor learning task in humans.
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