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. 2013 Oct 29;7:196. doi: 10.3389/fnins.2013.00196

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Copyright © 2013 Ortega, Lovejoy and Bernier.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Schematic diagrams of midsagittal sections through (A) the rainbow trout and (B) rat brains to summarize the contributions and interactions of the serotonergic and corticotropin-releasing factor (CRF) systems in the regulation of food intake. Serotonergic (5-HT) neurons from the dorsal raphe nucleus (DRN) can directly stimulate the release of CRF from the nucleus preoptic (NPO) and paraventricular nucleus (PVN) in fish and mammals, respectively. In mammals, 5-HT neurons also activate arcuate nucleus (ARC) neurons to facilitate the release of the melanocortin 4 receptor (MC4R) agonist α-melanocyte-stimulating hormone (αMSH) and inhibit the release of the MC4R antagonist agouti-related peptide (AgRP). CRF neurons in the PVN act as a downstream mediator of MC4R signaling and contribute to the regulation of food intake. In fish, while the anorexigenic actions of αMSH also appear to be mediated by the CRF-signaling pathway, the interactions between 5-HT and the melanocortin system have yet to be investigated. Also unknown are the roles of urotensin I (UI) and urocortin (UCN) secreting neurons as mediators of either the direct or indirect anorexigenic actions of 5-HT. Although CRF and UI/UCN have anorexigenic actions and both the CRF type 1 (CRF-R1) and type 2 (CRF-R2) receptors have been implicated in the regulation of food intake, the higher affinity of UI/UCN than CRF for CRF-R2 likely explains why UI/UCN more potently inhibits food intake than CRF (see text for further details). Abbreviations: cereb, cerebellum; cort, cerebral cortex; hyp, hypothalamus; NLT, nucleus lateralis tuberis; ob, olfactory bulb; rhomb, rhombencephalon; tect, optic tectum; tel, telencephalon.