Major depression is a highly prevalent severe mood disorder that is treated with antidepressants. The molecular targets of antidepressants require definition. We investigated the role of the acid sphingomyelinase (Asm)-ceramide system as a target for antidepressants. Therapeutic concentrations of the antidepressants amitriptyline and fluoxetine reduced Asm activity and ceramide concentrations in the hippocampus, increased neuronal proliferation, maturation and survival and improved behavior in mouse models of stress-induced depression. Genetic Asm deficiency abrogated these effects. Mice overexpressing Asm, heterozygous for acid ceramidase, treated with blockers of ceramide metabolism or directly injected with C16 ceramide in the hippocampus had higher ceramide concentrations and lower rates of neuronal proliferation, maturation and survival compared with controls and showed depression-like behavior even in the absence of stress. The decrease of ceramide abundance achieved by antidepressant-mediated inhibition of Asm normalized these effects. Lowering ceramide abundance may thus be a central goal for the future development of antidepressants. DOI: https://doi.org/10. 1038/nm.3214 Posted at the Zurich Open Repository and Archive, University of Zurich ZORA URL: https://doi.org/10.5167/uzh-79905 Accepted Version Originally published at: Gulbins, E; Palmada, M; Reichel, M; Lüth, A; Böhmer, C; Amato, D; Müller, C P; Tischbirek, C H; Groemer, T W; Tabatabai, G; Becker, K A; Tripal, P; Staedtler, S; Ackermann, T F; van Brederode, J; Alzheimer, C; Weller, M; Lang, U E; Kleuser, B; Grassme, H; Kornhuber, J (2013). Acid sphingomyelinaseceramide system mediates effects of antidepressant drugs. Nature Medicine, 19 (7) Major depression may be triggered by psychological stress, inflammatory cytokines, and dysfunction of the hypothalamic-pituitary-adrenal axis, etc. 1-4 .The previously held monoamine hypothesis for the action of antidepressants has been questioned because the antidepressant effect of these drugs is not clearly associated with their monoaminergic effect; in fact, the antidepressant tianeptine is even a serotonin reuptake enhancer 5 . Furthermore, the direct effect on monoamines contrasts with the delay of antidepressant effects in patients. Recent concepts of the pathogenesis of major depression suggest a change of cellular plasticity predominantly in the hippocampus and a shift in the balance between neurogenic and antiapoptotic events that leads to neurodegeneration and hippocampal atrophy [6][7][8][9] . Antidepressants increase neurogenesis and reverse hippocampal atrophy associated with major depression 9 .Here, we tested the role of the acid sphingomyelinase (EC 3.1.4.12, sphingomyelin phosphodiesterase, human protein: ASM, murine protein: Asm, gene symbol: Smpd1) and ceramide system as a target for antidepressants. Asm is ubiquitously expressed and releases ceramide from sphingomyelin, predominantly in lysosomes but also in secretory lysosomes and on the plasma membrane 10-13 .The antidepres...

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Summary Fibroblast growth factor 21 (FGF21) is a hormone induced by various metabolic stresses, including ketogenic and high carbohydrate diets, that regulates energy homeostasis. In humans, SNPs in and around the FGF21 gene have been associated with macronutrient preference, including carbohydrate, fat and protein intake. Here we show that FGF21 administration markedly reduces sweet and alcohol preference in mice, and sweet preference in cynomolgus monkeys. In mice, these effects require the FGF21 co-receptor β-Klotho in the central nervous system and correlate with reductions in dopamine concentrations in the nucleus accumbens. Since analogs of FGF21 are currently undergoing clinical evaluation for the treatment of obesity and type 2 diabetes, our findings raise the possibility that FGF21 administration could affect nutrient preference and other reward behaviors in humans.

Major depression and anxiety disorders have high prevalence rates and are frequently comorbid. The neurobiological bases for these disorders are not fully understood, and available treatments are not always effective. Current models assume that dysfunctions in neuronal proteins and peptide activities are the primary causes of these disorders. Brain lipids determine the localization and function of proteins in the cell membrane and in doing so regulate synaptic throughput in neurons. Lipids may also leave the membrane as transmitters and relay signals from the membrane to intracellular compartments or to other cells. Here we review how membrane lipids, which play roles in the membrane's function as a barrier and a signaling medium for classical transmitter signaling, contribute to depression and anxiety disorders and how this role may provide targets for lipid-based treatment approaches. Preclinical findings have suggested a crucial role for the membrane-forming n-3 polyunsaturated fatty acids, glycerolipids, glycerophospholipids, and sphingolipids in the induction of depression- and anxiety-related behaviors. These polyunsaturated fatty acids also offer new treatment options such as targeted dietary supplementation or pharmacological interference with lipid-regulating enzymes. While clinical trials support this view, effective lipid-based therapies may need more individualized approaches. Altogether, accumulating evidence suggests a crucial role for membrane lipids in the pathogenesis of depression and anxiety disorders; these lipids could be exploited for improved prevention and treatment. This article is part of a Special Issue entitled Brain Lipids.

Most people who are regular consumers of psychoactive drugs are not drug addicts, nor will they ever become addicts. In neurobiological theories, non-addictive drug consumption is acknowledged only as a "necessary" prerequisite for addiction, but not as a stable and widespread behavior in its own right. This target article proposes a new neurobiological framework theory for non-addictive psychoactive drug consumption, introducing the concept of "drug instrumentalization." Psychoactive drugs are consumed for their effects on mental states. Humans are able to learn that mental states can be changed on purpose by drugs, in order to facilitate other, non-drug-related behaviors. We discuss specific "instrumentalization goals" and outline neurobiological mechanisms of how major classes of psychoactive drugs change mental states and serve non-drug-related behaviors. We argue that drug instrumentalization behavior may provide a functional adaptation to modern environments based on a historical selection for learning mechanisms that allow the dynamic modification of consummatory behavior. It is assumed that in order to effectively instrumentalize psychoactive drugs, the establishment of and retrieval from a drug memory is required. Here, we propose a new classification of different drug memory subtypes and discuss how they interact during drug instrumentalization learning and retrieval. Understanding the everyday utility and the learning mechanisms of non-addictive psychotropic drug use may help to prevent abuse and the transition to drug addiction in the future.

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