IN THIS issue of Archives of General Psychiatry, Suhara et al1 suggest that dopamine (DA) D2 receptors in the anterior cingulate cortex (ACCX) are significantly reduced in drug-naïve patients with schizophrenia as compared with healthy controls, and that in the same subjects, D2 binding in that region correlates negatively with positive symptom scores on the Brief Psychiatric Rating Scale. This was based on positron emission tomography (PET) measurements of the "binding potential" (BP) of D2 receptors using the positron-emitting D2 (and D3 ) receptor radioligand [11C] FLB457. Binding potential is a common outcome measure that is widely used as a surrogate of Bmax (receptor density) but is influenced by several factors, including intrasynaptic DA concentration. In fact, the BP measurement carried out by PET was assumed to be a conglomerate of receptor parameters(not directly measured), including the absolute D2 DA Bmax in the brain, a free fraction of the unbound and dissociation constants of the radioligand, and the free concentration and dissociation constants of the competing endogenous DA. There was no significant correlation between BP and the negative symptoms or between BP and the age of onset or the duration of illness.
Wong DF. In Vivo Imaging of D2 Dopamine Receptors in SchizophreniaThe Ups and Downs of Neuroimaging Research. Arch Gen Psychiatry. 2002;59(1):31-34. doi:10.1001/archpsyc.59.1.31