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A 100% increase of dopaminergic cells in the olfactory bulb may explain hyposmia in Parkinson's disease

Authors

  • Evelien Huisman BSc,

    Corresponding author
    1. Department of Anatomy, Vrÿe Universiteit Medical Center, Amsterdam, The Netherlands
    • Department of Anatomy, VU University Medical Center, Graduate School Neurosciences Amsterdam, Van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands
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  • Harry B.M. Uylings PhD,

    1. Department of Anatomy, Vrÿe Universiteit Medical Center, Amsterdam, The Netherlands
    2. Netherlands Institute for Brain Research, Koninklÿke Nederlandse Akademie van Wettenschappen, Amsterdam, The Netherlands
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  • Piet V. Hoogland MD, PhD

    1. Department of Anatomy, Vrÿe Universiteit Medical Center, Amsterdam, The Netherlands
    2. Department of Anatomy and Histology, Faculty of Health Sciences, University of Stellenbosch, South Africa
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Abstract

Hyposmia is one of the most prevalent symptoms of Parkinson's disease. It may occur even before the motor symptoms start. To determine whether the olfactory dysfunctions, like the motor symptoms, are associated with a loss of dopamine, the number of dopaminergic cells in the olfactory bulb of Parkinson's disease patients was studied using tyrosine hydroxylase immunohistochemistry. The quantitative analysis reveals that the total number of tyrosine hydroxylase–immunoreactive neurons in the olfactory bulb is twice as high in Parkinson patients compared to age and gender-matched controls. Because dopamine is known to inhibit olfactory transmission in the olfactory glomeruli, we suggest that the increase of dopaminergic neurons in the olfactory bulb is responsible for the hyposmia in Parkinson patients. The increase of dopamine in the olfactory bulb explains why olfaction does not improve with levodopa therapy. © 2004 Movement Disorder Society

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