Stress Effects on the Mechanisms Regulating Appetite in Teleost Fish

The homeostatic regulation of food intake relies on a complex network involving peripheral and central signals that are integrated in the hypothalamus which in turn responds with the release of orexigenic or anorexigenic neuropeptides that eventually promote or inhibit appetite. Under stress conditions, the mechanisms that control food intake in fish are deregulated and the appetite signals in the brain do not operate as in control conditions resulting in changes in the expression of the appetite-related neuropeptides and usually a decreased food intake. The effect of stress on the mechanisms that regulate food intake in fish seems to be mediated in part by the corticotropin-releasing factor (CRF), an anorexigenic neuropeptide involved in the activation of the HPI axis during the physiological stress response. Furthermore, the melanocortin system is also involved in the connection between the HPI axis and the central control of appetite. The dopaminergic and serotonergic systems are activated during the stress response and they have also been related to the control of food intake. In addition, the central and peripheral mechanisms that mediate nutrient sensing capacity and hence implicated in the metabolic control of appetite are inhibited in fish under stress conditions. Finally, stress also affects peripheral endocrine signals such as leptin. In the present minireview, we summarize the knowledge achieved in recent years regarding the interaction of stress with the different mechanisms that regulate food intake in fish

Oral administration of melatonin counteracts several of the effects of chronic stress in rainbow trout

To assess a possible antistress role of melatonin in fish, we orally administered melatonin to rainbow trout for 10 d and then kept the fish under normal or high stocking density conditions during the last 4 d. Food intake; biochemical parameters in plasma (cortisol, glucose, and lactate concentrations); liver (glucose and glycogen concentrations, and glycogen synthase activity); enzyme activities of amylase, lipase, and protease in foregut and midgut; and content of the hypothalamic neurotransmitters dopamine and serotonin, as well as their oxidized metabolites, 3,4-dihydroxyphenylacetic acid and 5-hydroxy-3-indoleacetic acid, were evaluated under those conditions. High stocking density conditions alone induced changes indicative of stress conditions in plasma cortisol concentrations, liver glycogenolytic potential, the activities of some digestive enzymes, and the 3,4-dihydroxyphenylacetic acid-to-dopamine and 5-hydroxy-3-indoleacetic acid-to-serotonin ratios in the hypothalamus. Melatonin treatment in nonstressed fish induced an increase in liver glycogenolytic potential, increased the activity of some digestive enzymes, and enhanced serotoninergic and dopaminergic metabolism in hypothalamus. The presence of melatonin in stressed fish resulted in a significant interaction with cortisol concentrations in plasma, glycogen content, and glycogen synthase activity in liver and dopaminergic and serotoninergic metabolism in the hypothalamus. In general, the presence of melatonin mitigated several of the effects induced by stress, supporting an antistress role for melatonin in rainbow trout.Ministerio de Ciencia e Innovación | Ref. AGL2010-22247-C03-03Xunta de Galicia | Ref. CN2012/ 00

Neuroendocrine and Immune Responses Undertake Different Fates following Tryptophan or Methionine Dietary Treatment: Tales from a Teleost Model

Methionine and tryptophan appear to be fundamental in specific cellular pathways involved in the immune response mechanisms, including stimulation of T-regulatory cells by tryptophan metabolites or pro-inflammatory effects upon methionine supplementation. Thus, the aim of this study was to evaluate the immunomodulatory effect of these amino acids on the inflammatory and neuroendocrine responses in juveniles of European seabass, Dicentrarchus labrax. To achieve this, goal fish were fed for 14 days methionine and tryptophan-supplemented diets (MET and TRP, respectively, 2× dietary requirement level) or a control diet meeting the amino acids requirement levels (CTRL). Fish were sampled for immune status assessment and the remaining fish were challenged with intraperitoneally injected inactivated Photobacterium damselae subsp. piscicida and sampled either 4 or 24 h post-injection. Respiratory burst activity, brain monoamines, plasma cortisol, and immune-related gene expression showed distinct and sometimes opposite patterns regarding the effects of dietary amino acids. While neuroendocrine intermediates were not affected by any dietary treatment at the end of the feeding trial, both supplemented diets led to increased levels of plasma cortisol after the inflammatory insult, while brain monoamine content was higher in TRP-fed fish. Peripheral blood respiratory burst was higher in TRP-fed fish injected with the bacteria inoculum but only compared to those fed MET. However, no changes were detected in total antioxidant capacity. Complement factor 3 was upregulated in MET-fed fish but methionine seemed to poorly affect other genes expression patterns. In contrast, fish fed MET showed increased immune cells numbers both before and after immune challenge, suggesting a strong enhancing effect of methionine on immune cells proliferation. Differently, tryptophan effects on inflammatory transcripts suggested an inhibitory mode of action. This, together with a high production of brain monoamine and cortisol levels, suggests that tryptophan might mediate regulatory mechanisms of neuroendocrine and immune systems cooperation. Overall, more studies are needed to ascertain the role of methionine and tryptophan in modulating (stimulate or regulate) fish immune and neuroendocrine responses

MKK6 controls T3-mediated browning of white adipose tissue

El aumento de la capacidad termogénica del tejido adiposo para mejorar el gasto de energía del organismo se considera una estrategia terapéutica prometedora para combatir la obesidad. Aquí nosotros informe que la expresión del activador MAPK p38 MKK6 está elevada en el tejido adiposo blanco de individuos obesos. Usando animales knockout y shRNA, mostramos que la eliminación de Mkk6 aumenta el gasto de energía y la capacidad termogénica del tejido adiposo blanco, protegiendo a los ratones contra la obesidad inducida por la dieta y el desarrollo de la diabetes. La eliminación de Mkk6 aumenta la expresión de UCP1 estimulada por T3 en los adipocitos, lo que aumenta su capacidad termogénica. De manera mecánica, demostramos que, en el tejido adiposo blanco, p38 se activa mediante una ruta alternativa que involucra AMPK, TAK y TAB. Nuestros resultados identifican MKK6 en los adipocitos como un posible objetivo terapéutico para reducir la obesidad.Increasing the thermogenic capacity of adipose tissue to enhance organismal energy expenditure is considered a promising therapeutic strategy to combat obesity. Here, we report that expression of the p38 MAPK activator MKK6 is elevated in white adipose tissue of obese individuals. Using knockout animals and shRNA, we show that Mkk6 deletion increases energy expenditure and thermogenic capacity of white adipose tissue, protecting mice against diet-induced obesity and the development of diabetes. Deletion of Mkk6 increases T3-stimulated UCP1 expression in adipocytes, thereby increasing their thermogenic capacity. Mechanistically, we demonstrate that, in white adipose tissue, p38 is activated by an alternative pathway involving AMPK, TAK, and TAB. Our results identify MKK6 in adipocytes as a potential therapeutic target to reduce obesity.• Guadalupe Sabio Buzo y Rebeca Acin Pérez pertenecen a Programa Ramón y Cajal • Elisa Manieri pertenece a Caixa • Ministerio de Economía y Competitividad. Proyecto FPI BES-2014-069332, para Valle Montalvo Romeral • Ministerio de Economía y Competitividad. Proyecto FPI BES-2011-043428, para Edgar Bernardo • Ministerio de Economía y Competitividad y FEDER SAF2016-79126-R y Comunidad de Madrid S2010 / BMD-2326, para Guadalupe Sabio Buzo • ISCIII y FEDER, PI10 / 01692 e I3SNS-INT12 / 049, para Miguel Marcos Martín • Junta de Castilla y León GRS 681 / A / 11, para Lourdes Hernández Cosido • Ministerio de Economía y Competitividad. BFU2015-70664-R, Xunta de Galicia 2015-CP080 y PIE13 / 00024, y ERC281408, para Rubén Nogueiras Pozo • Unión Europea. Becas europeas UE0 / MCA1108 y UE0 / MCA1201; y la Comunidad de Madrid CAM / API1009, para Rubén Nogueiras Pozo • Junta de Extremadura y FEDER BR15164, para Francisco Centeno Velázquez • Ministerio de Economía y Competitividad. . BFU2013-46109-R, para Clara V. Álvarez Villamarín • European Union’s Seventh Framework Programme (FP7/2007-2013) under grant agreement no. ERC 260464peerReviewe

Feeding stimulation ability and central effects of intraperitoneal treatment of L-leucine, L-valine, and L-proline on amino acid sensing systems in rainbow trout: implication in food intake control

To continue gathering knowledge on the central regulation of food intake in response to amino acids in teleost fish, using as a model rainbow trout (Oncorhynchus mykiss), we evaluated in a first experiment the feeding attractiveness of L-leucine, L-valine, and L-proline offered as an agar gel matrix. In a second experiment, we assessed the effect of intraperitoneal (IP) treatment with the same amino acids on food intake. In a third experiment, we carried out a similar IP administration of amino acids to evaluate the response of amino acid sensing mechanisms in the hypothalamus and telencephalon. Results are discussed in conjunction with an earlier study where leucine and valine were administered intracerebroventricularly (ICV). The attractiveness of amino acids does not appear to relate to their effects on food intake, at least when administrated by-passing ingestion and luminal absorption, since two attractive amino acids resulted in an anorexigenic (Leu) or no effects (Pro) on food intake while a non-attractive amino acid (Val) induced anorexigenic (IP treatment) or orexigenic (ICV treatment) responses. The effects of Leu on food intake might relate to the expression of hypothalamic neuropeptides and result from the direct activation of amino acid sensing systems. In contrast, while valine had few effects on hypothalamic amino acid sensing systems after ICV treatment, a significant amount of parameters become affected by IP treatment suggesting that the effect of Val after IP treatment is indirect. Proline had no relevant effects on amino acid sensing systems, neuropeptide expression, and food intake, which suggest that this amino acid might not have a relevant role in the homeostatic regulation of food intake through hypothalamic mechanisms. In telencephalon, the same amino acid sensing systems operating in hypothalamus appear to be present and respond to Leu and Val, but it is still unclear how they might relate to the control of food intake.Ministerio de Educación, Cultura y Deporte | Ref. FPU16/00045Agencia Estatal de Investigación | Ref. AGL2016-74857-C3-1-RAgencia Estatal de Investigación | Ref. IJCI-2016-3049

REV-ERBα agonist SR9009 promotes a negative energy balance in goldfish

REV-ERBα (nr1d1, nuclear receptor subfamily 1 group D member 1) is a transcriptional repressor that in mammals regulates nutrient metabolism, and has effects on energy homeostasis, although its role in teleosts is poorly understood. To determine REV-ERBα’s involvement in fish energy balance and metabolism, we studied the effects of acute and 7-day administration of its agonist SR9009 on food intake, weight and length gain, locomotor activity, feeding regulators, plasma and hepatic metabolites, and liver enzymatic activity. SR9009 inhibited feeding, lowering body weight and length gain. In addition, the abundance of ghrelin mRNA decreased in the intestine, and abundance of leptin-aI mRNA increased in the liver. Hypocretin, neuropeptide y (npy), and proopiomelanocortin (pomc) mRNA abundance was not modified after acute or subchronic SR9009 administration, while hypothalamic cocaine- and amphetamine-regulated transcript (cartpt-I) was induced in the subchronic treatment, being a possible mediator of the anorectic effects. Moreover, SR9009 decreased plasma glucose, coinciding with increased glycolysis and a decreased gluconeogenesis in the liver. Decreased triglyceride levels and activity of lipogenic enzymes suggest a lipogenesis reduction by SR9009. Energy expenditure by locomotor activity was not significantly affected by SR9009. Overall, this study shows for the first time in fish the effects of REV-ERBα activation via SR9009, promoting a negative energy balance by reducing energetic inputs and regulating lipid and glucose metabolism.Ministerio de Ciencia e Innovación | Ref. PID2019-103969RBC32Ministerio de Ciencia e Innovación | Ref. PID2019-103969RBC31Universidad Complutense de Madrid | Ref. CT42/18-CT43-1

Central treatment of ketone body in rainbow trout alters liver metabolism without apparently altering the regulation of food intake

We hypothesize that the presence in fish brain of a ketone body (KB) like β-hydroxybutyrate (BHB) alters energy homeostasis through effects on food intake and peripheral energy metabolism. Using rainbow trout (Oncorhynchus mykiss) as a model, we intracerebroventricularly (ICV) administered 1 μl 100 g–1 body mass of saline solution alone (control) or containing 0.5 μmol of BHB. In a fist set of experiments, BHB did not affect food intake 6 and 24 h after treatment. In a second set of experiments, we evaluated 6 h after ICV BHB treatment changes in parameters putatively related to food intake control in brain areas (hypothalamus and hindbrain) involved in nutrient sensing and changes in energy metabolism in liver. The absence of changes in food intake might relate to the absence of major changes in the cascade of events from the detection of KB through ketone-sensing mechanisms, changes in transcription factors, and changes in the mRNA abundance of neuropeptides regulating food intake. This response is different than that of mammals. In contrast, central administration of BHB induced changes in liver energy metabolism suggesting a decreased use of glucose and probably an enhanced use of amino acid and lipid. These responses in liver are different to those of mammals under similar treatments but comparable to those occurring in fish under food deprivation conditions.Agencia Estatal de Investigación (AEI) | Ref. AGL2016-74857-C3-1-RXunta de Galicia | Ref. ED413B 2019/37Ministerio de Educación, Cultura y Deporte | Ref. FPU16/00045Xunta de Galicia | Ref. ED481B2018/01

Feeding Stimulation Ability and Central Effects of Intraperitoneal Treatment of L-Leucine, L-Valine, and L-Proline on Amino Acid Sensing Systems in Rainbow Trout: Implication in Food Intake Control

To continue gathering knowledge on the central regulation of food intake in response to amino acids in teleost fish, using as a model rainbow trout (Oncorhynchus mykiss), we evaluated in a first experiment the feeding attractiveness of L-leucine, L-valine, and L-proline offered as an agar gel matrix. In a second experiment, we assessed the effect of intraperitoneal (IP) treatment with the same amino acids on food intake. In a third experiment, we carried out a similar IP administration of amino acids to evaluate the response of amino acid sensing mechanisms in the hypothalamus and telencephalon. Results are discussed in conjunction with an earlier study where leucine and valine were administered intracerebroventricularly (ICV). The attractiveness of amino acids does not appear to relate to their effects on food intake, at least when administrated by-passing ingestion and luminal absorption, since two attractive amino acids resulted in an anorexigenic (Leu) or no effects (Pro) on food intake while a non-attractive amino acid (Val) induced anorexigenic (IP treatment) or orexigenic (ICV treatment) responses. The effects of Leu on food intake might relate to the expression of hypothalamic neuropeptides and result from the direct activation of amino acid sensing systems. In contrast, while valine had few effects on hypothalamic amino acid sensing systems after ICV treatment, a significant amount of parameters become affected by IP treatment suggesting that the effect of Val after IP treatment is indirect. Proline had no relevant effects on amino acid sensing systems, neuropeptide expression, and food intake, which suggest that this amino acid might not have a relevant role in the homeostatic regulation of food intake through hypothalamic mechanisms. In telencephalon, the same amino acid sensing systems operating in hypothalamus appear to be present and respond to Leu and Val, but it is still unclear how they might relate to the control of food intake

Influence of vegetable diets on physiological and immune responses to thermal stress in Senegalese sole (Solea senegalensis)

The substitution of fish resources as ingredients for aquafeeds by those based on vegetable sources is needed to ensure aquaculture sustainability in the future. It is known that Senegalese sole (Solea senegalensis) accepts high dietary content of plant ingredients without altering growth or flesh quality parameters. However, scarce information is available regarding the long-term impact of vegetable diets (combining the inclusion of both vegetable protein and oils) on the stress response and immunity of this fish species. This study aims to evaluate the concomitant effect of the extended use of vegetable protein-based diets with fish oil (FO) replacement (0, 50 or 100%) by vegetable oils (VO), on the response to acute (10 min) or prolonged (4 days) stress, induced by thermal shock. Plasma levels of cortisol, glucose and lactate as well as hepatic levels of glucose, glycogen and lactate were evaluated as primary and secondary responses to stress, 6 and 18 months after feeding the experimental diets (6 and 18 MAF). The brain monoaminergic activity in telencephalon and hypothalamus, and non-specific immune parameters were also evaluated. As expected, thermal shock induced an increase in values of plasma parameters related to stress, which was more evident in acute than in prolonged stress. Stress also affected lactate levels in the liver and the values of the alternative complement pathway-ACH50 in the plasma. Dietary substitution of FO induced an effect per se on some parameters such as decreased hepatic glucose and glycogen levels and peroxidase activity in plasma as well enhanced serotonergic activity in brain of non-stressed fish. The results obtained in some parameters indicate that there is an interaction between the use of vegetable diets with the physiological response to thermal stress, as is the case of the hepatic lactate, serotonergic neurotransmission in brain, and the activity of ACH50 in plasma. These results suggest that the inclusion of VO in plant protein based diets point to a slightly inhibited stress response, more evident for an acute than a prolonged stress.Agencia Estatal de Investigación | Ref. AGL 2016-74857-C3-1-RXunta de GaliciaFundação para a Ciência e a Tecnologi