Increased dopamine D2 receptor binding and enhanced apomorphine-induced locomotor activity in μ-opioid receptor knockout mice

Lu Tai Tien, Younjoo Park, Lir Wan Fan, Tangeng Ma, Horace H. Loh, Ing Kang Ho

Research output: Contribution to journalArticlepeer-review

30 Scopus citations

Abstract

Previous studies from our laboratory have indicated possible interactions between opioidergic and dopaminergic neurons in the central nervous system. In this study, apomorphine-induced locomotor activity and the D1 and D2 subtype dopamine receptor binding were examined in mice lacking the μ-opioid receptor genes. The ambulatory time, vertical time and total motor distance of locomotor activity were measured after administration of apomorphine (2mg/kg, i.p.) for a period of 90min. The autoradiographic studies of D1 and D2 dopamine receptors were conducted using [3H] SCH23390 and [3H] raclopride as ligand, respectively. In wild type mice that received apomorphine, 2mg/kg, i.p., the locomotor activity such as ambulatory time, vertical time and total motor distance were not significantly altered as compared with that of the saline control group. However, the locomotor activity measured was significantly increased in the same dose of apomorphine treated μ-opioid receptor knockout mice between 5 and 40min after administration. The results obtained also show that the binding of D2 dopamine receptor in μ-opioid receptor knockout mice was significantly higher than that of the wild type in the caudate putamen. However, the binding of the D1 dopamine receptor in μ-opioid receptor knockout mice was not significantly different from that of the wild type. It appears that the apomorphine treated μ-opioid receptor knockout mice showed enhancement in locomotor activity. The enhanced locomotor activity may be related to the compensatory up-regulation of D2 dopamine receptors in mice lacking μ-opioid receptor genes.

Original languageEnglish (US)
Pages (from-to)109-115
Number of pages7
JournalBrain Research Bulletin
Volume61
Issue number1
DOIs
StatePublished - Jun 30 2003

Bibliographical note

Funding Information:
The authors wish to thank Dr. I.A. Paul and Dr. B. Lee for their equipment and advice and Ann Pace for her editorial assistance on this manuscript. This study was supported by the Human Science Grant Foundation of Japan.

Copyright:
Copyright 2017 Elsevier B.V., All rights reserved.

Keywords

  • Apomorphine
  • Autoradiography
  • D1 and D2 receptors
  • Locomotor activity
  • μ-Opioid receptor knockout mice

Fingerprint

Dive into the research topics of 'Increased dopamine D2 receptor binding and enhanced apomorphine-induced locomotor activity in μ-opioid receptor knockout mice'. Together they form a unique fingerprint.

Cite this