Dopamine receptor binding imaging

Other functional imaging studies of the DA system have reported decreased Di receptor density (Dagher et al. 2001), increased F-DOPA uptake (a marker for increased DA turnover) (Salokangas et al. 2000), and both decreased (Krause et al. 2002) and no alterations (Staley et al. 2001) in dopamine transporter binding in smokers. 

It is well known that typical neuroleptics, all of which have a high affinity for dopamine receptors (particularly D2 receptors), do not effectively treat all schizophrenic patients and have only limited beneficial effects on the negative symptoms of the illness. Furthermore, neither typical nor atypical neuroleptics have an immediate effect on the positive symptoms even though it can be shown by both experimental studies in animals and by imaging methods in schizophrenic patients that neuroleptics rapidly bind to dopamine receptors. Thus factors other than an overactive dopaminergic system are probably operative in this disorder. The question is which of the numerous neurotransmitters and modulatory neuropeptides are responsible for both the negative symptoms and the delay in onset of the therapeutic effects of neuroleptics on the positive symptoms ... 

A 38-year-old man with schizophrenia secretively smoked marijuana during a neuroimaging study. A comparison of two sets of images, before and after marijuana inhalation, showed a 20% reduction in the striatal dopamine D2 receptor binding ratio, suggestive of increased synaptic dopaminergic activity. 

Fig. 11.1 C-11 raclopride images of a patient with schizophrenia before and after treatment with Ziprasidone, which binds to dopamine, serotonin and alpha-adrenergic receptors in the basal ganglia.

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