Patients with right-hemisphere strokes (N = 9) more than 1 year after injury had greater cortical binding of (3-N-[11C]methyl)spiperone than a similar group of patients with left-hemisphere strokes (N = 8) or normal control subjects (N = 17). The higher S2 serotonin receptor binding occurred in uninjured regions of the right parietal and temporal cortex. The ratio of binding in the ipsilateral to contralateral cortex showed a significant negative correlation with severity of depression scores in the left temporal cortex. These findings suggest that the biochemical response of the brain may be different depending on which hemisphere is injured and that some depressions may be a consequence of the failure to upregulate serotonin receptors after stroke.
There is growing evidence that there are subtypes of schizophrenia (Bowen et al., 2019; Chand et al., 2020). Specifically, messenger ribonucleic acid (mRNA) gene expression findings on postmortem dorsolateral prefrontal cortex (DLPFC) suggest that schizophrenia patients can be divided into two groups, those with a relatively normal DLPFC transcriptome (Type 1) and those with hundreds of differentially expressed genes (Type 2). The clinical relevance of that finding is limited by the fact that autopsy tissue is required to distinguish Type 1 from Type 2 patients, however the PET target sphingosine-1-phosphate receptor-1 (S1PR1) is among the genes whose mRNA expression is upregulated in Type 2 compared to Type 1 patients (Bowen et al., 2019). As a preliminary study to validate this PET target, S1PR1 protein expression was assessed by receptor autoradiography and immunohistochemistry in the DLPFC from schizophrenic patients classified as Type 1 or Type 2 based on their DLPFC transcriptomes and from controls. S1PR1 protein expression is upregulated in Type 2 compared to Type 1 (p < 0.05) supporting the possibility that positron emission tomography (PET) can be used as a clinical test to distinguish these subgroups of schizophrenic patients during life.
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