Early studies investigating molecular abnormalities in the brain of subjects with psychiatric illness measured levels of neurotransmitter and their metabolites in the brain or the activity of neuronal specific enzymes (Bird et al., 1979). The development of radioactive ligands that specifically bound to an increasingly diverse number of target sites then made it possible to measure other molecules in the brain, such as neurotransmitter receptors (Mackay et al., 1982) and transporters (Stanley et al., 1990). Initially such experiments were carried out using particulate membrane prepared from dissected brain regions. However, whilst this approach had the advantage of allowing extensive characterisation of molecules in brain tissue, it could not localise any change to a discrete area within specific brain regions.