Limbic selectivity of clozapine

Fractal analysis--a new approach in brain receptor imaging

Improvements in detector technology and the development of radioligands for brain receptor imaging have introduced exiting new insights into the pathophysiology of various neuropsychiatric disorders and have improved the possibilities of optimizing the treatment for patients suffering from them. Positron emission tomography (PET) and single-photon emission tomography (SPET) with tailored radiopharmaceuticals provide information on the topographic physiological chemistry of the living human brain. The different patterns of brain receptor densities and distribution can be imaged and modelled with PET and SPET. The normal receptor distribution in the brain is broadly heterogeneous with different cortical layers, which show receptor densities varying from very low to high. Further exploration of the data shows that human neurophysiology and neural architectures possess fractal properties that may be altered during activation and in different neuropsychiatric disorders. This review highlights recent findings in SPET receptor imaging and the use of fractal analysis in the interpretation of images representing various neuropsychiatric disorders.

The cerebral cortex: a case for a common site of action of antipsychotics

Recent evidence from studies of receptor occupancy and regulation in post-mortem brains of patients with neuropsychiatric disorders and in non-human primates is providing new leads in the ongoing quest to understand the pathophysiology and causes of schizophrenia and to develop more effective methods of treatment. These studies suggest that the cerebral cortex may harbour the elusive common sites of action of antipsychotic medications and indicate that chronic treatment with these drugs differentially regulates both families of dopamine receptors in this structure. Upregulation of the cortical dopamine D2 receptors is accompanied by a downregulation of the D1 sites. Balancing the opposing actions of dopamine D1 and D2 receptor regulation may hold the key to optimal drug therapy and to understanding the pathophysiology of schizophrenia. In this article, Michael Lidow, Graham Williams and Patricia Goldman-Rakic review the evidence supporting the cerebral cortex as a pivotal site for these mechanisms underlying the action of antipsychotics.