G protein-coupled receptors (GPCRs, or GPRs) contain 7 transmembrane domains and transduce extracellular signals through heterotrimeric G proteins. GPCR GPR55 is a member of this family (subfamily Orphan-A). It has been reported to be expressed in the brain, where mRNA transcripts were detected in the caudate nucleus and putamen, but not detected in the hippocampus, thalamus, pons cerebellum, frontal cortex of the brain. ESTs have been isolated from liver/spleen libraries.