Ghrelin, the endogenous agonist of the growth hormone secretagogue receptor, has been shown to induce robust feeding responses in numerous experimental models. Although ghrelin comes from both peripheral and central sources, its hyperphagic properties, to a large extent, arise from activity at the brain level. The current review focuses on describing central mechanisms through which this peptide affects consumption. We address the issue of whether ghrelin serves just as a signal of energy needs of the organism or -as suggested by the most recent findings -also affects food intake via other feeding-related mechanisms, including reward and memory. Complexity of ghrelin's role in the regulation of ingestive behavior is discussed by characterizing its influence on consumption, reward and memory as well as by defining its function within the brain circuitry and interplay with other neuropeptides.
Keywordsghrelin; food intake; reward; energy; brain
Ghrelin and its receptor: the beginningsBowers et al. discovered synthetic peptides that stimulated and amplified the release of growth hormone (GH) by acting at the hypothalamus and the pituitary (Bowers et al., 1980;Bowers et al., 1984). Their GH hypophysiotropic activity was distinct from the action of growth hormone releasing hormone (GHRH) and it was GHRH-independent. They were classified as growth hormone-releasing peptides (GHRPs) and growth hormone secetagogues (GHSs) (for review, see (Smith, 2005)).