The endocannabinoid system consists of cannabinoid receptors (which mediate the actions of cannabis), their endogenous ligands (endocannabinoids), and the enzymes and proteins associated with their regulation. In brain, the endocannabinoid system functions to modulate the release of other neurotransmitters via the subtype 1 (CB1) receptor. Abnormalities of CB1 receptor expression or endocannabinoid transmission have been associated with several neuropsychiatric diseases. Subtype 2 (CB2) receptors are found primarily on immune and neuroimmune cells and are overexpressed in states of inflammation and neuroinflammation. Both receptors are of particular interest for biomarker development and therapeutic targets. Growing evidence supports the regulation of endocannabinoids as involved in neuropsychiatric and neuroinflammatory diseases. However, the function of endocannabinoid system components in vivo remains difficult to assess. Therefore, the use of functional imaging techniques, such as positron emission tomography (PET), may be particularly useful in the assessment and quantification of the endocannabinoid system. This chapter will cover the current understanding of functional imaging that directly targets the endocannabinoid system.
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