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S11.B Iron–dopamine connection: cellular studies and possible mechanism
Parallel Symposia / Sleep Medicine 8 Suppl. 1 (2007) S11–S47 (5) the potential advantages and disadvantages of computerized sleep recordings. The evidence review suggested that computer scoring and quantitative analysis of sleep is still in the stage of development. For many technical specification decisions, little or no direct evidence was found, although basic engineering principles or standard practices provided some rationale which was utilized to develop the recommendations formulated during on the subsequent UCLA/Rand standardized consensus process.
S10.D Title to be established T. Shimizu. Akita University, Japan Abstract not available at time of printing.
S11. Finding the dopamine abnormality in RLS: the iron–dopamine connection evaluated in translational research
S11.1 Symposium summary R.P. Allen. Neurology and Sleep Medicine, Johns Hopkins University, Baltimore, MD 21224, USA This is both a trans-continental (Europe and America) and multiple discipline (Neurology, Psychology, Nutrition and Neuroscience) symposium. This symposium focuses on one of the most active areas of research into pathology of RLS and addresses the major puzzle of why dopaminergic medications work. The iron-deficiency model provides a basis for translational research to solve the mystery of the dopamine pathology in RLS. This will be of interest both to the clinician in terms of the basis for and potential changes in dopamine treatments and for the clinical scientists in terms of types of studies to be done in the future • Chair: Wolfgang Oertel, University of Marburg, Germany • 1st speaker: John Beard, University of Pennsylvania, University Park, PA, USA • 2nd speaker: Christopher Earley, Johns Hopkins University, Baltimore, MD, USA • 3rd speaker: James Connor, University of Pennsylvania, School of Medicine, Hershey, PA, USA • 4th speaker/discussant: Richard Allen, Johns Hopkins University, Baltimore, MD, USA Although dopaminergic medications have been demonstrated to be clearly effective for treatment of RLS the scant and conflicting evidence for dopaminergic pathology fails to indicate much about the nature of any dopamine abnormality. This leaves us uncertain what studies or treatments we should be looking at in the future. Understanding the biology related to the primary treatment could lead to better treatment and perhaps methods to minimize the augmentation problem with dopamine treatment. Since iron insufficiency appears to cause RLS it provides one approach to finding the dopamine abnormality. The translational research covered in this symposium uses the interaction of clinical, autopsy, animal, and cellular studies to unravel the effects of iron on dopamine in RLS. The results are somewhat surprising indicating increased dopamine production in moderate to severe RLS with an increased amplitude of the circadian pattern. These results provide a basis for the effectiveness of dopaminergic treatment and also provide a broader appreciation of the dopamine abnormalities in RLS suggesting, in particular, problems with synaptic functioning. The program starts with exploring dopamine abnormalities produced in the iron-deficient animal models of RLS. This is followed by a review of the cellular effects of iron deficiency based on iron chelation studies. The RLS autopsy material will then be presented noting similarities and differences from the animal and cell models. Finally an update on recent CSF and imaging studies in RLS patients will be presented in relation to the results from the prior presentations. The differences in the clinical results between the German and the American studies will also be reviewed in light of the general iron–dopamine relationships that have been discovered.
S17
S11.A Iron deficiency alters monoamine catabolism as well as feedback regulation of DA transporter functioning L.E. Bianco, D.M. Konrad, J.L. Beard. Penn State University, University Park, PA, USA Brain iron deficiency is believed to be related to the alterations in dopamine metabolism reported in PET studies of patients with RLS. Previous animal research has shown that iron deficiency (ID) causes decreased dopamine (DA) D2 receptor density, decreased DA transporter (DAT) density and alters DA signaling in the brain. There has been little suggestion in the literature regarding the integrity of the autoreceptor-DA transporter feedback loop nor evidence that monoamine catabolism are altered by striatal iron deficiency. We used a post-weaning rat model to show that ID results in a 61% decrease in MAO-B activity in striatum but there was no effect on MAO-A or COMT activity. No net flux experiments demonstrated that ID increases extracellular dopamine by 26% and decreases extraction fraction (Ed) by 20% implying the DAT function is decreased by ID. In vivo microdialysis using direct infusion of 1 mM FeSO4 showed that elevations of extracellular DA were normalized with iron treatment. Administration of a D2 agonist (5mM quinpirole) during NNF decreased extracellular DA for both control (CN) and ID groups despite a lower D2 density in ID rats. Quinpirole infusion increased Ed by 45% in CN animals, however there was no change in ID Ed. This lack of response indicates disruption in the signal pathway regulating DAT functionality and may explain responses of RLS patients to DR agonists and antagonists. Long term studies with D2 agonists are underway to explore sensitization and augmentation biology within this model of brain iron deficiency in RLS. S11.B Iron–dopamine connection: cellular studies and possible mechanism C.J. Earley. Department of Neurology, Johns Hopkins University, Baltimore, MD, USA Iron deficiency (ID) is considered to be one of the primary environmental factors for developing RLS. But even in those who do not have peripheral ID, low brain iron appears to be a underlying factor. CSF, MRI, cranial ultrasound and autopsy studies have all indicated low iron as a potential primary pathology in many patients with RLS. As levodopa is the most effective treatment for RLS, it has been hypothesized that dopamine (DA) is low in RLS. The original hypothesis was that ID leads to decreased tyrosine hydroxylase (TH), as iron is a co-factor for this enzyme, and thus lead to decreased DA and RLS symptoms. However studies have shown that ID increases TH and DA production, which is the opposite of that predicted. Studies in animals have shown that ID will reduce D2R and DAT, suggesting that the primary effect of ID is on receptor or transport with feedback upregulation of TH. However, there is no known direct connection between iron and D2R or DAT at any level. Recent studies in striatal tissue have shown that glutamate (GluR) and adenosine (AR) receptors form heteromers with dopamine receptors (DR) and lead to decrease DR number or function, thus raising the possibility that ID may act on these receptors to subsequently modify D2R. In vitro cellular studies using desferroxamine to induce cellular ID; and mice made ID by diet or with natural genetic difference in striatal iron were used to explore the effects of ID to these receptors. The findings of these studies and the complex interaction between the various receptors in the striatum will be discussed in this presentation. Contributed support: NIH research support. S11.C The dopaminergic profile in the putamen and substantia nigra in restless leg syndrome J.R. Connor1 , X.-S. Wang1 , R.P. Allen2 , J.L. Beard3 , J.A. Wiesinger3 , B.T. Felt4 , C.J. Earley2 . 1 Department of Neurosurgery, Penn State College of Medicine, Hershey, PA, USA, 2 Department of Neurology, Johns Hopkins University, Baltimore, MD, USA, 3 Department of Nutrition, Penn State University, University Park, PA, USA, 4 Center for Human Growth and Development, The University of Michigan, Ann Arbor, MI, USA Background: Restless leg syndrome (RLS) is a sensorimotor disorder that disrupts sleep. Clinical studies have implicated the dopaminergic system in RLS, while others have suggested that RLS is associated with insufficient levels of brain iron. These concepts may not be mutually exclusive because
S10.D Title to be established T. Shimizu. Akita University, Japan Abstract not available at time of printing.
S11. Finding the dopamine abnormality in RLS: the iron–dopamine connection evaluated in translational research
S11.1 Symposium summary R.P. Allen. Neurology and Sleep Medicine, Johns Hopkins University, Baltimore, MD 21224, USA This is both a trans-continental (Europe and America) and multiple discipline (Neurology, Psychology, Nutrition and Neuroscience) symposium. This symposium focuses on one of the most active areas of research into pathology of RLS and addresses the major puzzle of why dopaminergic medications work. The iron-deficiency model provides a basis for translational research to solve the mystery of the dopamine pathology in RLS. This will be of interest both to the clinician in terms of the basis for and potential changes in dopamine treatments and for the clinical scientists in terms of types of studies to be done in the future • Chair: Wolfgang Oertel, University of Marburg, Germany • 1st speaker: John Beard, University of Pennsylvania, University Park, PA, USA • 2nd speaker: Christopher Earley, Johns Hopkins University, Baltimore, MD, USA • 3rd speaker: James Connor, University of Pennsylvania, School of Medicine, Hershey, PA, USA • 4th speaker/discussant: Richard Allen, Johns Hopkins University, Baltimore, MD, USA Although dopaminergic medications have been demonstrated to be clearly effective for treatment of RLS the scant and conflicting evidence for dopaminergic pathology fails to indicate much about the nature of any dopamine abnormality. This leaves us uncertain what studies or treatments we should be looking at in the future. Understanding the biology related to the primary treatment could lead to better treatment and perhaps methods to minimize the augmentation problem with dopamine treatment. Since iron insufficiency appears to cause RLS it provides one approach to finding the dopamine abnormality. The translational research covered in this symposium uses the interaction of clinical, autopsy, animal, and cellular studies to unravel the effects of iron on dopamine in RLS. The results are somewhat surprising indicating increased dopamine production in moderate to severe RLS with an increased amplitude of the circadian pattern. These results provide a basis for the effectiveness of dopaminergic treatment and also provide a broader appreciation of the dopamine abnormalities in RLS suggesting, in particular, problems with synaptic functioning. The program starts with exploring dopamine abnormalities produced in the iron-deficient animal models of RLS. This is followed by a review of the cellular effects of iron deficiency based on iron chelation studies. The RLS autopsy material will then be presented noting similarities and differences from the animal and cell models. Finally an update on recent CSF and imaging studies in RLS patients will be presented in relation to the results from the prior presentations. The differences in the clinical results between the German and the American studies will also be reviewed in light of the general iron–dopamine relationships that have been discovered.
S17
S11.A Iron deficiency alters monoamine catabolism as well as feedback regulation of DA transporter functioning L.E. Bianco, D.M. Konrad, J.L. Beard. Penn State University, University Park, PA, USA Brain iron deficiency is believed to be related to the alterations in dopamine metabolism reported in PET studies of patients with RLS. Previous animal research has shown that iron deficiency (ID) causes decreased dopamine (DA) D2 receptor density, decreased DA transporter (DAT) density and alters DA signaling in the brain. There has been little suggestion in the literature regarding the integrity of the autoreceptor-DA transporter feedback loop nor evidence that monoamine catabolism are altered by striatal iron deficiency. We used a post-weaning rat model to show that ID results in a 61% decrease in MAO-B activity in striatum but there was no effect on MAO-A or COMT activity. No net flux experiments demonstrated that ID increases extracellular dopamine by 26% and decreases extraction fraction (Ed) by 20% implying the DAT function is decreased by ID. In vivo microdialysis using direct infusion of 1 mM FeSO4 showed that elevations of extracellular DA were normalized with iron treatment. Administration of a D2 agonist (5mM quinpirole) during NNF decreased extracellular DA for both control (CN) and ID groups despite a lower D2 density in ID rats. Quinpirole infusion increased Ed by 45% in CN animals, however there was no change in ID Ed. This lack of response indicates disruption in the signal pathway regulating DAT functionality and may explain responses of RLS patients to DR agonists and antagonists. Long term studies with D2 agonists are underway to explore sensitization and augmentation biology within this model of brain iron deficiency in RLS. S11.B Iron–dopamine connection: cellular studies and possible mechanism C.J. Earley. Department of Neurology, Johns Hopkins University, Baltimore, MD, USA Iron deficiency (ID) is considered to be one of the primary environmental factors for developing RLS. But even in those who do not have peripheral ID, low brain iron appears to be a underlying factor. CSF, MRI, cranial ultrasound and autopsy studies have all indicated low iron as a potential primary pathology in many patients with RLS. As levodopa is the most effective treatment for RLS, it has been hypothesized that dopamine (DA) is low in RLS. The original hypothesis was that ID leads to decreased tyrosine hydroxylase (TH), as iron is a co-factor for this enzyme, and thus lead to decreased DA and RLS symptoms. However studies have shown that ID increases TH and DA production, which is the opposite of that predicted. Studies in animals have shown that ID will reduce D2R and DAT, suggesting that the primary effect of ID is on receptor or transport with feedback upregulation of TH. However, there is no known direct connection between iron and D2R or DAT at any level. Recent studies in striatal tissue have shown that glutamate (GluR) and adenosine (AR) receptors form heteromers with dopamine receptors (DR) and lead to decrease DR number or function, thus raising the possibility that ID may act on these receptors to subsequently modify D2R. In vitro cellular studies using desferroxamine to induce cellular ID; and mice made ID by diet or with natural genetic difference in striatal iron were used to explore the effects of ID to these receptors. The findings of these studies and the complex interaction between the various receptors in the striatum will be discussed in this presentation. Contributed support: NIH research support. S11.C The dopaminergic profile in the putamen and substantia nigra in restless leg syndrome J.R. Connor1 , X.-S. Wang1 , R.P. Allen2 , J.L. Beard3 , J.A. Wiesinger3 , B.T. Felt4 , C.J. Earley2 . 1 Department of Neurosurgery, Penn State College of Medicine, Hershey, PA, USA, 2 Department of Neurology, Johns Hopkins University, Baltimore, MD, USA, 3 Department of Nutrition, Penn State University, University Park, PA, USA, 4 Center for Human Growth and Development, The University of Michigan, Ann Arbor, MI, USA Background: Restless leg syndrome (RLS) is a sensorimotor disorder that disrupts sleep. Clinical studies have implicated the dopaminergic system in RLS, while others have suggested that RLS is associated with insufficient levels of brain iron. These concepts may not be mutually exclusive because