Alastair S Garfield

Publications (14)104.56 Total impact

• Article: Neurochemical characterization of body weight-regulating leptin receptor neurons in the nucleus of the solitary tract.

  Alastair S Garfield, Christa Patterson, Susanne Skora, Fiona M Gribble, Frank Reimann, Mark L Evans, Martin G Myers, Lora K Heisler
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  ABSTRACT: The action of peripherally released leptin at long-form leptin receptors (LepRb) within the brain represents a fundamental axis in the regulation of energy homeostasis and body weight. Efforts to delineate the neuronal mediators of leptin action have recently focused on extrahypothalamic populations and have revealed that leptin action within the nucleus of the solitary tract (NTS) is critical for normal appetite and body weight regulation. To elucidate the neuronal circuits that mediate leptin action within the NTS, we employed multiple transgenic reporter lines to characterize the neurochemical identity of LepRb-expressing NTS neurons. LepRb expression was not detected in energy balance-associated NTS neurons that express cocaine- and amphetamine-regulated transcript, brain-derived neurotrophic factor, neuropeptide Y, nesfatin, catecholamines, γ-aminobutyric acid, prolactin-releasing peptide, or nitric oxide synthase. The population of LepRb-expressing NTS neurons was comprised of subpopulations marked by a proopiomelanocortin-enhanced green fluorescent protein (EGFP) transgene and distinct populations that express proglucagon and/or cholecystokinin. The significance of leptin action on these three populations of NTS neurons was assessed in leptin-deficient Ob/Ob mice, revealing increased NTS proglucagon and cholecystokinin, but not proopiomelanocortin, expression. These data provide new insight into the appetitive brainstem circuits engaged by leptin.
  Endocrinology 08/2012; 153(10):4600-7. · 4.46 Impact Factor
• Source

  Available from: PubMed Central

  Article: Recurrent hypoglycemia is associated with loss of activation in rat brain cingulate cortex.

  Paul Hurst, Alastair S Garfield, Claire Marrow, Lora K Heisler, Mark L Evans
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  ABSTRACT: A subset of people with diabetes fail to mount defensive counterregulatory responses (CRR) to hypoglycemia. Although the mechanisms by which this occurs remain unclear, recurrent exposure to hypoglycemia may be an important etiological factor. We hypothesized that loss of CRR to recurrent exposure to hypoglycemia represents a type of stress desensitization, in which limbic brain circuitry involved in modulating stress responses might be implicated. Here, we compared activation of limbic brain regions associated with stress desensitization during acute hypoglycemia (AH) and recurrent hypoglycemia (RH). Healthy Sprague Dawley rats were exposed to either acute or recurrent 3-d hypoglycemia. We also examined whether changes in neuronal activation were caused directly by the CRR itself by infusing epinephrine, glucagon, and corticosterone without hypoglycemia. AH increased neuronal activity as quantified by c-fos immunoreactivity (FOS-IR) in the cingulate cortex and associated ectorhinal and perirhinal cortices but not in an adjacent control area (primary somatosensory cortex). FOS-IR was not observed after hormone infusion, suggesting that AH-associated activation was caused by hypoglycemia rather than by CRR. Importantly, AH FOS-IR activation was significantly blunted in rats exposed to RH. In conclusion, analogous with other models of stress habituation, activation in the cingulate cortex and associated brain areas is lost with exposure to RH. Our data support the hypothesis that limbic brain areas may be associated with the loss of CRR to RH in diabetes.
  Endocrinology 03/2012; 153(4):1908-14. · 4.46 Impact Factor
• Article: Leptin does not directly affect CNS serotonin neurons to influence appetite.

  Daniel D Lam, Gina M Leinninger, Gwendolyn W Louis, Alastair S Garfield, Oliver J Marston, Rebecca L Leshan, Erica L Scheller, Lyndsay Christensen, Jose Donato, Jing Xia, Mark L Evans, Carol Elias, Jeffrey W Dalley, Denis I Burdakov, Martin G Myers, Lora K Heisler
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  ABSTRACT: Serotonin (5-HT) and leptin play important roles in the modulation of energy balance. Here we investigated mechanisms by which leptin might interact with CNS 5-HT pathways to influence appetite. Although some leptin receptor (LepRb) neurons lie close to 5-HT neurons in the dorsal raphe (DR), 5-HT neurons do not express LepRb. Indeed, while leptin hyperpolarizes some non-5-HT DR neurons, leptin does not alter the activity of DR 5-HT neurons. Furthermore, 5-HT depletion does not impair the anorectic effects of leptin. The serotonin transporter-cre allele (Sert(cre)) is expressed in 5-HT (and developmentally in some non-5-HT) neurons. While Sert(cre) promotes LepRb excision in a few LepRb neurons in the hypothalamus, it is not active in DR LepRb neurons, and neuron-specific Sert(cre)-mediated LepRb inactivation in mice does not alter body weight or adiposity. Thus, leptin does not directly influence 5-HT neurons and does not meaningfully modulate important appetite-related determinants via 5-HT neuron function.
  Cell metabolism 05/2011; 13(5):584-91. · 17.35 Impact Factor
• Source

  Available from: Cy Yueh

  Article: Glucokinase inhibitor glucosamine stimulates feeding and activates hypothalamic neuropeptide Y and orexin neurons.

  Ligang Zhou, Chen-Yu Yueh, Daniel D Lam, Jill Shaw, Mayowa Osundiji, Alastair S Garfield, Mark Evans, Lora K Heisler
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  ABSTRACT: Maintaining glucose levels within the appropriate physiological range is necessary for survival. The identification of specific neuronal populations, within discreet brain regions, sensitive to changes in glucose concentration has led to the hypothesis of a central glucose-sensing system capable of directly modulating feeding behaviour. Glucokinase (GK) has been identified as a glucose-sensor responsible for detecting such changes both within the brain and the periphery. We previously reported that antagonism of centrally expressed GK by administration of glucosamine (GSN) was sufficient to induce protective glucoprivic feeding in rats. Here we examine a neurochemical mechanism underlying this effect and report that GSN stimulated food intake is highly correlated with the induction of the neuronal activation marker cFOS within two nuclei with a demonstrated role in central glucose sensing and appetite, the arcuate nucleus of the hypothalamus (ARC) and lateral hypothalamic area (LHA). Furthermore, GSN stimulated cFOS within the ARC was observed in orexigenic neurons expressing the endogenous melanocortin receptor antagonist agouti-related peptide (AgRP) and neuropeptide Y (NPY), but not those expressing the anorectic endogenous melanocortin receptor agonist alpha-melanocyte stimulating hormone (α-MSH). In the LHA, GSN stimulated cFOS was found within arousal and feeding associated orexin/hypocretin (ORX), but not orexigenic melanin-concentrating hormone (MCH) expressing neurons. Our data suggest that GK within these specific feeding and arousal related populations of AgRP/NPY and ORX neurons may play a modulatory role in the sensing of and appetitive response to hypoglycaemia.
  Behavioural brain research 03/2011; 222(1):274-8. · 3.22 Impact Factor
• Article: Role of central serotonin and melanocortin systems in the control of energy balance.

  Oliver J Marston, Alastair S Garfield, Lora K Heisler
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  ABSTRACT: Body weight homeostasis is critically dependent upon the convergence and integration of multiple central and peripheral signalling systems that collectively function to detect and elicit physiological and behavioural responses to nutritional state. To date, only a minority of these signals have been pharmacologically targeted for the treatment of human obesity. One signal that has been effectively manipulated to reduce body weight is the neurotransmitter serotonin (5-hydroxytryptamine; 5-HT); however, the relevant downstream signalling pathways are incompletely understood. Recently, the melanocortin system, a nexus for multiple modulators of energy balance, has emerged as one key mediator of serotonin's effects on appetite. Here we review the serotonin and melanocortin systems with reference to their roles in energy balance and discuss the evidence that the two systems are functionally linked.
  European journal of pharmacology 01/2011; 660(1):70-9. · 2.59 Impact Factor
• Source

  Available from: u-szeged.hu

  Article: Distinct physiological and behavioural functions for parental alleles of imprinted Grb10.

  Alastair S Garfield, Michael Cowley, Florentia M Smith, Kim Moorwood, Joanne E Stewart-Cox, Kerry Gilroy, Sian Baker, Jing Xia, Jeffrey W Dalley, Laurence D Hurst, Lawrence S Wilkinson, Anthony R Isles, Andrew Ward
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  ABSTRACT: Imprinted genes, defined by their preferential expression of a single parental allele, represent a subset of the mammalian genome and often have key roles in embryonic development, but also postnatal functions including energy homeostasis and behaviour. When the two parental alleles are unequally represented within a social group (when there is sex bias in dispersal and/or variance in reproductive success), imprinted genes may evolve to modulate social behaviour, although so far no such instance is known. Predominantly expressed from the maternal allele during embryogenesis, Grb10 encodes an intracellular adaptor protein that can interact with several receptor tyrosine kinases and downstream signalling molecules. Here we demonstrate that within the brain Grb10 is expressed from the paternal allele from fetal life into adulthood and that ablation of this expression engenders increased social dominance specifically among other aspects of social behaviour, a finding supported by the observed increase in allogrooming by paternal Grb10-deficient animals. Grb10 is, therefore, the first example of an imprinted gene that regulates social behaviour. It is also currently alone in exhibiting imprinted expression from each of the parental alleles in a tissue-specific manner, as loss of the peripherally expressed maternal allele leads to significant fetal and placental overgrowth. Thus Grb10 is, so far, a unique imprinted gene, able to influence distinct physiological processes, fetal growth and adult behaviour, owing to actions of the two parental alleles in different tissues.
  Nature 01/2011; 469(7331):534-8. · 36.28 Impact Factor
• Article: Brain serotonin system in the coordination of food intake and body weight.

  Daniel D Lam, Alastair S Garfield, Oliver J Marston, Jill Shaw, Lora K Heisler
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  ABSTRACT: An inverse relationship between brain serotonin and food intake and body weight has been known for more than 30 years. Specifically, augmentation of brain serotonin inhibits food intake, while depletion of brain serotonin promotes hyperphagia and weight gain. Through the decades, serotonin receptors have been identified and their function in the serotonergic regulation of food intake clarified. Recent refined genetic studies now indicate that a primary mechanism through which serotonin influences appetite and body weight is via serotonin 2C receptor (5-HT(2C)R) and serotonin 1B receptor (5-HT(1B)R) influencing the activity of endogenous melanocortin receptor agonists and antagonists at the melanocortin 4 receptor (MC4R). However, other mechanisms are also possible and the challenge of future research is to delineate them in the complete elucidation of the complex neurocircuitry underlying the serotonergic control of appetite and body weight.
  Pharmacology Biochemistry and Behavior 11/2010; 97(1):84-91. · 2.53 Impact Factor
• Article: Derivation of primary mouse embryonic fibroblast (PMEF) cultures.

  Alastair S Garfield
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  ABSTRACT: Primary mouse embryonic fibroblasts (PMEFs) have a number of properties that make them an attractive cell culture model. Relative to other primary explant cultures they are easy to establish and maintain, proliferate rapidly and, as a result, large numbers of cells can be produced from a single embryo within several days following explantation. This allows, for instance, for ready comparison of wild-type and knockout cells derived from the same litter of animals. PMEFs can be expanded through several passages before they reach crisis and can be used to establish cell lines following spontaneous transformation or following derivation from strains carrying mutations, such as in the gene encoding the tumour suppressor Trp53. They have been widely used as feeders to support other cultured cell types, notably embryonic stem cells, as well as for the study of a diverse range of cellular phenomena using microscopic, biochemical and molecular biological techniques. Here, we describe a simple and reliable method for the derivation and maintenance of PMEFs.
  Methods in molecular biology (Clifton, N.J.) 01/2010; 633:19-27.
• Article: Transgenic mice expressing green fluorescent protein under the control of the corticotropin-releasing hormone promoter.

  Tamar Alon, Ligang Zhou, Cristian A Pérez, Alastair S Garfield, Jeffrey M Friedman, Lora K Heisler
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  ABSTRACT: CRH is widely expressed in the brain and is of broad functional relevance to a number of physiological processes, including stress response, parturition, immune response, and ingestive behavior. To delineate further the organization of the central CRH network, we generated mice expressing green fluorescent protein (GFP) under the control of the CRH promoter, using bacterial artificial chromosome technology. Here we validate CRH-GFP transgene expression within specific brain regions and confirm the distribution of central GFP-producing cells to faithfully recapitulate that of CRH-expressing cells. Furthermore, we confirm the functional integrity of a population of GFP-producing cells by demonstrating their opposite responsiveness to nutritional status. We anticipate that this transgenic model will lend itself as a highly tractable tool for the investigation of CRH expression and function in discrete brain regions.
  Endocrinology 10/2009; 150(12):5626-32. · 4.46 Impact Factor
• Article: Nutritional state influences Nociceptin/Orphanin FQ peptide receptor expression in the dorsal raphe nucleus.

  Magdalena J Przydzial, Alastair S Garfield, Daniel D Lam, Stephen P Moore, Mark L Evans, Lora K Heisler
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  ABSTRACT: Agonists of the nociceptin/orphanin FQ (N/OFQ) peptide (NOP) receptor stimulate food intake. Concordantly, neuroanatomical localization of NOP receptor mRNA has revealed it to be highly expressed in brain regions associated with the regulation of energy balance. However, the specific mechanisms and neurochemical pathways through which physiological N/OFQ influences appetite are not well understood. To investigate this, we examined nutritional state-associated changes in NOP receptor mRNA levels throughout the rostrocaudal extent of the rat brain using in situ hybridization histochemistry (ISHH) and quantitative densitometry analysis. We observed a significant downregulation of NOP receptor mRNA in the dorsal raphe nucleus (DRN) of fasted rats compared to free-feeding rats. In contrast, no difference in NOP receptor mRNA expression was observed in the supraoptic, parventricular, ventromedial, arcuate or dorsomedial nuclei of the hypothalamus, the red nucleus, the locus coeruleus or the hypoglossal nucleus in the fasted or fed state. These data suggest that the endogenous N/OFQ system is responsive to changes in energy balance and that NOP receptors specifically within the DRN may be physiologically relevant to N/OFQ's effects on appetite.
  Behavioural brain research 09/2009; 206(2):313-7. · 3.22 Impact Factor
• Article: Role of central melanocortin pathways in energy homeostasis.

  Alastair S Garfield, Daniel D Lam, Oliver J Marston, Magdalena J Przydzial, Lora K Heisler
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  ABSTRACT: The rise in the global prevalence of human obesity has emphasized the need for a greater understanding of the physiological mechanisms that underlie energy homeostasis. Numerous circulating nutritional cues and central neuromodulatory signals are integrated within the brain to regulate both short- and long-term nutritional state. The central melanocortin system represents a crucial point of convergence for these signals and, thus, has a fundamental role in regulating body weight. The melanocortin ligands, synthesized in discrete neuronal populations within the hypothalamus and brainstem, modulate downstream homeostatic signalling via their action at central melanocortin-3 and -4 receptors. Intimately involved in both ingestive behaviour and energy expenditure, the melanocortin system has garnered much interest as a potential therapeutic target for human obesity.
  Trends in Endocrinology and Metabolism 07/2009; 20(5):203-15. · 8.11 Impact Factor
• Article: Loss of the imprinted snoRNA mbii-52 leads to increased 5htr2c pre-RNA editing and altered 5HT2CR-mediated behaviour.

  Christine M Doe, Dinko Relkovic, Alastair S Garfield, Jeffrey W Dalley, David E H Theobald, Trevor Humby, Lawrence S Wilkinson, Anthony R Isles
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  ABSTRACT: The Prader-Willi syndrome (PWS) genetic interval contains several brain-expressed small nucleolar (sno)RNA species that are subject to genomic imprinting. In vitro studies have shown that one of these snoRNA molecules, h/mbii-52, negatively regulates editing and alternative splicing of the serotonin 2C receptor (5htr2c) pre-RNA. However, the functional consequences of loss of h/mbii-52 and subsequent increased post-transcriptional modification of 5htr2c are unknown. 5HT2CRs are important in controlling aspects of cognition and the cessation of feeding, and disruption of their function may underlie some of the psychiatric and feeding abnormalities seen in PWS. In a mouse model for PWS lacking expression of mbii-52 (PWS-IC+/-), we show an increase in editing, but not alternative splicing, of the 5htr2c pre-RNA. This change in post-transcriptional modification is associated with alterations in a number of 5HT2CR-related behaviours, including impulsive responding, locomotor activity and reactivity to palatable foodstuffs. In a non-5HT2CR-related behaviour, marble burying, loss of mbii-52 was without effect. The specificity of the behavioural effects to changes in 5HT2CR function was further confirmed using drug challenges. These data illustrate, for the first time, the physiological consequences of altered RNA editing of 5htr2c linked to mbii-52 loss that may underlie specific aspects of the complex PWS phenotype and point to an important functional role for this imprinted snoRNA.
  Human Molecular Genetics 04/2009; 18(12):2140-8. · 7.64 Impact Factor
• Article: Pharmacological targeting of the serotonergic system for the treatment of obesity.

  Alastair S Garfield, Lora K Heisler
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  ABSTRACT: The attenuation of food intake as induced by an increase in serotonergic (5-hydroxytryptamine, 5-HT) efficacy has been a target of antiobesity pharmacotherapies. However, the induction of tolerance and/or side-effects limited the clinical utility of the earliest serotonin-related medications. With the global prevalence of obesity rising, there has been renewed interest in the manipulation of the serotonergic system as a point of pharmacological intervention. The serotonin(2C) receptor (5-HT(2C)R), serotonin(1B) (rodent)/serotonin(1Dbeta) (human) receptor (5-HT(1B/1Dbeta)R) and serotonin(6) receptor (5-HT(6)R) represent the most promising serotonin receptor therapeutic targets. Canonical serotonin receptor compounds have given way to a myriad of novel receptor-selective ligands, many of which have observable anorectic effects. Here we review serotonergic compounds reducing ingestive behaviour and discuss their clinical potential for the treatment of obesity.
  The Journal of Physiology 12/2008; 587(Pt 1):49-60. · 4.72 Impact Factor
• Article: Mice with a disruption of the imprinted Grb10 gene exhibit altered body composition, glucose homeostasis, and insulin signaling during postnatal life.

  Florentia M Smith, Lowenna J Holt, Alastair S Garfield, Marika Charalambous, Francoise Koumanov, Mark Perry, Reto Bazzani, Steven A Sheardown, Bronwyn D Hegarty, Ruth J Lyons, Gregory J Cooney, Roger J Daly, Andrew Ward
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  ABSTRACT: The Grb10 adapter protein is capable of interacting with a variety of receptor tyrosine kinases, including, notably, the insulin receptor. Biochemical and cell culture experiments have indicated that Grb10 might act as an inhibitor of insulin signaling. We have used mice with a disruption of the Grb10 gene (Grb10Delta2-4 mice) to assess whether Grb10 might influence insulin signaling and glucose homeostasis in vivo. Adult Grb10Delta2-4 mice were found to have improved whole-body glucose tolerance and insulin sensitivity, as well as increased muscle mass and reduced adiposity. Tissue-specific changes in insulin receptor tyrosine phosphorylation were consistent with a model in which Grb10, like the closely related Grb14 adapter protein, prevents specific protein tyrosine phosphatases from accessing phosphorylated tyrosines within the kinase activation loop. Furthermore, insulin-induced IRS-1 tyrosine phosphorylation was enhanced in Grb10Delta2-4 mutant animals, supporting a role for Grb10 in attenuation of signal transmission from the insulin receptor to IRS-1. We have previously shown that Grb10 strongly influences growth of the fetus and placenta. Thus, Grb10 forms a link between fetal growth and glucose-regulated metabolism in postnatal life and is a candidate for involvement in the process of fetal programming of adult metabolic health.
  Molecular and Cellular Biology 09/2007; 27(16):5871-86. · 5.53 Impact Factor