Penny C Staton,
Jon P Hatcher, Deborah J Walker,
Alastair D Morrison,
Ellen M Shapland,
Jane P Hughes,
Elizabeth Chong,
Palwinder K Mander,
Paula J Green,
Andy Billinton,
Michael Fulleylove,
Hilary C Lancaster,
Jason C Smith,
Leigh T Bailey,
Alan Wise,
Andrew J Brown,
Jill C Richardson,
Iain P Chessell
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ABSTRACT: It has been postulated that the G protein-coupled receptor, GPR55, is a third cannabinoid receptor. Given that the ligands at the CB(1) and CB(2) receptors are effective analgesic and anti-inflammatory agents, the role of GPR55 in hyperalgesia associated with inflammatory and neuropathic pain has been investigated. As there are no well-validated GPR55 tool compounds, a GPR55 knockout (GPR55(-/-)) mouse line was generated and fully backcrossed onto the C57BL/6 strain. General phenotypic analysis of GPR55(-/-) mice revealed no obvious primary differences, compared with wild-type (GPR55(+/+)) littermates. GPR55(-/-) mice were then tested in the models of adjuvant-induced inflammation and partial nerve ligation. Following intraplantar administration of Freund's complete adjuvant (FCA), inflammatory mechanical hyperalgesia was completely absent in GPR55(-/-) mice up to 14 days post-injection. Cytokine profiling experiments showed that at 14 days post-FCA injection there were increased levels of IL-4, IL-10, IFN gamma and GM-CSF in paws from the FCA-injected GPR55(-/-) mice when compared with the FCA-injected GPR55(+/+) mice. This suggests that GPR55 signalling can influence the regulation of certain cytokines and this may contribute to the lack of inflammatory mechanical hyperalgesia in the GPR55(-/-) mice. In the model of neuropathic hypersensitivity, GPR55(-/-) mice also failed to develop mechanical hyperalgesia up to 28 days post-ligation. These data clearly suggest that the manipulation of GPR55 may have therapeutic potential in the treatment of both inflammatory and neuropathic pain.
Pain 06/2008; 139(1):225-36. · 5.78 Impact Factor
