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Brain Advance Access published online on November 29, 2007
Brain, doi:10.1093/brain/awm255
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© 2007 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Review Article

Imaging of opioid receptors in the central nervous system

Gjermund Henriksen1,2 and Frode Willoch3,4

1Nuklearmedizinische Klinik und Poliklinik, Klinikum rechts der Isar, Technische Universität München, Ismaningerstrasse 22, D-81675 München, Germany, 2Department of Chemistry, University of Oslo, PO Box 1033, N-0315, 3Department of Radiology, Aker University Hospital, Trondheimsveien 235, N-0514 and 4Center for Molecular Biology and Neuroscience, PO Box 1105 Blindern, N-0317 Oslo, Norway

Correspondence to: Frode Willoch, Department of Radiology, Aker University Hospital, Trondheimsveien 235, N-0514 Oslo, Norway. E-mail: frode.willoch{at}labmed.uio.no

In vivo functional imaging by means of positron emission tomography (PET) is the sole method for providing a quantitative measurement of µ-, {kappa} and {delta}-opioid receptor-mediated signalling in the central nervous system. During the last two decades, measurements of changes to the regional brain opioidergic neuronal activation—mediated by endogenously produced opioid peptides, or exogenously administered opioid drugs—have been conducted in numerous chronic pain conditions, in epilepsy, as well as by stimulant- and opioidergic drugs. Although several PET-tracers have been used clinically for depiction and quantification of the opioid receptors changes, the underlying mechanisms for regulation of changes to the availability of opioid receptors are still unclear. After a presentation of the general signalling mechanisms of the opioid receptor system relevant for PET, a critical survey of the pharmacological properties of some currently available PET-tracers is presented. Clinical studies performed with different PET ligands are also reviewed and the compound-dependent findings are summarized. An outlook is given concluding with the tailoring of tracer properties, in order to facilitate for a selective addressment of dynamic changes to the availability of a single subclass, in combination with an optimization of the quantification framework are essentials for further progress in the field of in vivo opioid receptor imaging.

Key Words: PET; opioid receptors; pain; epilepsy; addiction

Abbreviations: ACC, anterior cingulate cortex; BP, binding potential; BPND, BP using reference tissue method; Bavail, concentration of available receptor; CAF, carfentanil; DPN, diprenorphine; FC, frontal cortex; FDPN, 6-O-desmethyl-2-fluoroethyl-diprenorphine; FCyF, fluoro-cyclofoxy; fMRI, functional magnetic resonance imaging; GPCR, guanine nucleotide-binding protein coupled receptor; KD, radioligand equilibrium dissociation constant; MeNTl, methyl-naltrindole; NA, nucleus accumbens; NMDA, N-methyl-D-asparate; DV, volume of distribution; DVR, volume of distribution ratio; VOI, volume of interest; SM1, primary sensorimotor cortex; SA, spectral analysis; SPM, statistical parametric mapping; VT, volume of distribution.

Received May 15, 2007. Revised September 3, 2007. Accepted September 25, 2007.


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