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Am J Physiol Regul Integr Comp Physiol 292: R575-R585, 2007. First published August 17, 2006; doi:10.1152/ajpregu.00448.2006
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SLEEP AND TEMPERATURE REGULATION

Ghrelin microinjection into forebrain sites induces wakefulness and feeding in rats

¹Department of Veterinary and Comparative Anatomy, Pharmacology and Physiology, Neuroscience Program, Washington State University, Pullman, Washington; and ²Department of Biological Sciences, Fordham University, Bronx, New York

Submitted 29 June 2006 ; accepted in final form 9 August 2006

Ghrelin, a gut-brain peptide, is best known for its role in the stimulation of feeding and growth hormone release. In the brain, orexin, neuropeptide Y (NPY), and ghrelin are parts of a food intake regulatory circuit. Orexin and NPY are also implicated in maintaining wakefulness. Previous experiments in our laboratory revealed that intracerebroventricular injections of ghrelin induce wakefulness in rats. To further elucidate the possible role of ghrelin in the regulation of arousal, we studied the effects of microinjections of ghrelin into hypothalamic sites, which are implicated in the regulation of feeding and sleep, such as the lateral hypothalamus (LH), medial preoptic area (MPA), and paraventricular nucleus (PVN) on sleep in rats. Sleep responses, motor activity, and food intake after central administration of 0.04, 0.2, or 1 µg (12, 60, or 300 pmol) ghrelin were recorded. Microinjections of ghrelin into the LH had strong wakefulness-promoting effects lasting for 2 h. Wakefulness was also stimulated by ghrelin injection into the MPA and PVN; the effects were confined to the first hour after the injection. Ghrelin's non-rapid-eye-movement sleep-suppressive effect was accompanied by attenuation in the electroencephalographic (EEG) slow-wave activity and changes in the EEG power spectrum. Food consumption was significantly stimulated after microinjections of ghrelin into each hypothalamic site. Together, these results are consistent with the hypothesis that forebrain ghrelinergic mechanisms play a role in the regulation of vigilance, possibly through activating the components of the food intake- and arousal-promoting network formed by orexin and NPY.

lateral hypothalamus; medial preoptic area; paraventricular nucleus; electroencephalogram; slow-wave activity; sleep

This article has been cited by other articles:

				E. Szentirmai, L. Kapas, Y. Sun, R. G. Smith, and J. M. Krueger Spontaneous sleep and homeostatic sleep regulation in ghrelin knockout mice Am J Physiol Regulatory Integrative Comp Physiol, July 1, 2007; 293(1): R510 - R517. [Abstract] [Full Text] [PDF]

				P. C. Yannielli, P. C. Molyneux, M. E. Harrington, and D. A. Golombek Ghrelin Effects on the Circadian System of Mice J. Neurosci., March 14, 2007; 27(11): 2890 - 2895. [Abstract] [Full Text] [PDF]

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