Small-Animal PET Study of Adenosine A(1) Receptors in Rat Brain: Blocking Receptors and Raising Extracellular Adenosine

Soumen Paul, Shivashankar Khanapur, Anna A. Rybczynska, Chantal Kwizera, Jurgen W. A. Sijbesma, Kiichi Ishiwata, Antoon T. M. Willemsen, Philip H. Elsinga, Rudi A. J. O. Dierckx, Aren van Waarde*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

19 Citations (Scopus)

Abstract

Activation of adenosine A(1) receptors (A(1)R) in the brain causes sedation, reduces anxiety, inhibits seizures, and promotes neuroprotection. Cerebral A(1)R can be visualized using 8-dicyclopropylmethyl-1-C-11-methyl-3-propyl-xanthine (C-11-MPDX) and PET. This study aims to test whether C-11-MPDX can be used for quantitative studies of cerebral A1R in rodents. Methods: C-11-MPDX was injected (intravenously) into isoflurane-anesthetized male Wistar rats (300 g). A dynamic scan of the central nervous system was obtained, using a small-animal PET camera. A cannula in a femoral artery was used for blood sampling. Three groups of animals were studied: group 1, controls (saline-treated); group 2, animals pretreated with the A(1)R antagonist 8-cyclopentyl-1, 3-dipropylxanthine (DPCPX, 1 mg, intraperitoneally); and group 3, animals pretreated (intraperitoneally) with a 20% solution of ethanol in saline (2 mL) plus the adenosine kinase inhibitor 4-amino-5-(3-bromophenyl)-7-(6-morpholino-pyridin-3-yl)pyrido [2,3-d] pyrimidine dihydrochloride (ABT-702) (1 mg). DPCPX is known to occupy cerebral A1R, whereas ethanol and ABT-702 increase extracellular adenosine. Results: In groups 1 and 3, the brain was clearly visualized. High uptake of C-11-MPDX was noted in striatum, hippocampus, and cerebellum. In group 2, tracer uptake was strongly suppressed and regional differences were abolished. The treatment of group 3 resulted in an unexpected 40%-45% increase of the cerebral uptake of radioactivity as indicated by increases of PET standardized uptake value, distribution volume from Logan plot, nondisplaceable binding potential from 2-tissue-compartment model fit, and standardized uptake value from a biodistribution study performed after the PET scan. The partition coefficient of the tracer (K-1/k(2) from the model fit) was not altered under the study conditions. Conclusion: C-11-MPDX shows a regional distribution in rat brain consistent with binding to A(1)R. Tracer binding is blocked by the selective A(1)R antagonist DPCPX. Pretreatment of animals with ethanol and adenosine kinase inhibitor increases C-11-MPDX uptake. This increase may reflect an increased availability of A(1)R after acute exposure to ethanol.

Original languageEnglish
Pages (from-to)1293-1300
Number of pages8
JournalJournal of Nuclear Medicine
Volume52
Issue number8
DOIs
Publication statusPublished - 1-Aug-2011

Keywords

  • receptors
  • adenosine A1
  • adenosine kinase inhibitor
  • brain
  • positron emission tomography (PET)
  • ethanol
  • POSITRON-EMISSION-TOMOGRAPHY
  • INDUCED MOTOR INCOORDINATION
  • CENTRAL-NERVOUS-SYSTEM
  • KINASE INHIBITORS
  • NUCLEOSIDE TRANSPORTERS
  • BASAL FOREBRAIN
  • ETHANOL
  • ADENOSINE-A1-RECEPTORS
  • MICRODIALYSIS
  • METABOLISM

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