Several studies have examined the link between the
cannabinoid CB1 receptor and several neuropsychiatric illnesses, including
schizophrenia. As such, there is a need for in vivo imaging tracers so that the relationship between CB1 and
schizophrenia (SZ) can be further studied. In this paper, we present our first human studies in both healthy control patients and patients with
schizophrenia using the novel PET tracer, [(11)C]OMAR (
JHU75528), we have shown its utility as a tracer for imaging human CB1 receptors and to investigate normal aging and the differences in the
cannabinoid system of healthy controls versus patients with
schizophrenia. A total of ten healthy controls and nine patients with
schizophrenia were included and studied with high specific activity [(11)C]OMAR. The CB1 binding (expressed as the distribution volume; V(T)) was highest in the globus pallidus and the cortex in both controls and patients with
schizophrenia. Controls showed a correlation with the known distribution of CB1 and decline of [(11)C]OMAR binding with age, most significantly in the globus pallidus. Overall, we observed elevated mean binding in patients with
schizophrenia across all regions studied, and this increase was statistically significant in the pons (p<0.05), by the Students t-test. When we ran a regression of the control subjects V(T) values with age and then compared the patient data to 95% prediction limits of the linear regression, three patients fell completely outside for the globus pallidus, and in all other regions there were at least 1-3 patients outside of the prediction intervals. There was no statistically significant correlations between PET measures and the individual Brief Psychiatry Rating Score (BPRS) subscores (r=0.49), but there was a significant correlation between V(T) and the ratio of the BPRS
psychosis to withdrawal score in the frontal lobe (r=0.60), and middle and posterior cingulate regions (r=0.71 and r=0.79 respectively). In conclusion, we found that [(11)C] OMAR can image human CB1 receptors in normal aging and
schizophrenia. In addition, our initial data in subjects with
schizophrenia seem to suggest an association of elevated binding specific brain regions and symptoms of the disease.