Neurochemical brain imaging investigations of schizophrenia

Neurochemical brain imaging methods developed over the past 20 years offer significant promise for elucidating the biochemical underpinnings of schizo phrenia. The two general methodologies used for these studies have been: 1) radiotracer imaging: PET (positron emission tomography) and SPECT (single photon emission computed tomography); and 2) NMR (nuclear magnetic resonanc e) imaging: fMRI (functional magnetic resonance imaging) and MRS (magnetic resonance spectroscopy). Despite conflicting findings, striatal D-2 recepto r density may be elevated in some, but not all patients. Elevated synthesis , and increased release of dopamine after amphetamine challenge have also b een reported. Imaging of cortical 5-HT2A receptors suggests that this syste m is unaffected, in conflict with findings of postmortem studies. Although prior postmortem studies suggested an increase in cortical GABA(A) receptor s, three SPECT studies have found no significant changes. MRS studies have shown decreased levels of NAA (N-acetyl-aspartate) moieties in hippocampus and frontal cortex of schizophrenic patients, which is consistent with the reported loss of neurons and neuropil in postmortem brains. In conclusion, developments in radiotracer and NMR imaging have provided promising leads t o the biochemical abnormalities associated with schizophrenia. Future signi ficant understanding is likely to occur with the development of new probes and enhanced instrument technology, when applied with an appreciation of th e heterogeneity of the disorder and the need for careful clinical assessmen t of patients. Biol Psychiatry 1999;46:600-615 (C) 1999 Society of Biologic al Psychiatry.