Previous Positron Emission Tomography Imaging Research Articles

117.3 Imaging Microglial Activation in Clinical High Risk for Psychosis and Untreated First-Episode Psychosis: A PET StudyW [18F]FEPPA

Abstract Background: A role of the immune system in the pathogenesis of schizophrenia is supported by convergence of evidence from genetic, epidemiology, and preclinical studies. Previous positron emission tomography (PET) studies using radioligands that target the translocator protein 18kDa (TSPO) in patients with schizophrenia in vivo were limited by radioligand used, resolution of scanners used, and the confounding effect of antipsychotic medications. There is a dearth of evidence on the state of early stages of the illness such as the first-episode psychosis (FEP) and clinical high risk for psychosis (CHR). Methods: Using a second-generation TSPO radioligand, [18F]FEPPA, and a high-resolution research tomograph (HRRT), we examined microglial activation in dorsolateral prefrontal cortex (DLPFC) and hippocampus of CHR and FEP. Dynamic PET data were analyzed using a 2-tissue compartment model with an arterial plasma input function to obtain [18F]FEPPA total volume of distribution (VT), as previously validated. Based on their rs6971 polymorphism, subjects were classified as high-, medium- or low-affinity [18F]FEPPA binders, and all the analyses were controlled for genotype. Results: 24 (mean age = 21.21, SD = 3.35) CHR and 19 patients with untreated FEP (mean age = 27.53, SD = 6.78), and 20 healthy volunteers (mean age =27.75, SD = 8.77) underwent PET and magnetic resonance imaging. No significant differences in [18F]FEPPA VT in DLPFC and hippocampus were found between different diagnostic groups. Explorative association analyses found a trend toward significant association between RBANS total score and [18F]FEPPA VT in hippocampus of FEP (r = .50, P = .04). In CHR, apathy score was associated with [18F]FEPPA VT in DLPFC (r = .604, P = .003) and hippocampus (r = .574, P = .005). Moreover, [18F]FEPPA VT in DLPFC was associated with state anxiety score (r = .56, P = .007). Conclusion: This is the largest study examined microglial activation in the early stages of psychosis using a standard methodology without the confound of antipsychotic medications. Our findings suggest that microglial activation is not present in early stages of psychosis (i.e., CHR and FEP).

Exploring the impact of BDNF Val66Met genotype on serotonin transporter and serotonin-1A receptor binding.

BackgroundThe brain-derived neurotrophic factor (BDNF) Val66Met polymorphism (rs6265) may impact on the in-vivo binding of important serotonergic structures such as the serotonin transporter (5-HTT) and the serotonin-1A (5-HT1A) receptor. Previous positron emission tomography (PET) studies on the association between Val66Met and 5-HTT and 5-HT1A binding potential (BPND) have demonstrated equivocal results.MethodsWe conducted an imaging genetics study investigating the effect of Val66Met genotype on 5-HTT or 5-HT1A BPND in 92 subjects. Forty-one subjects (25 healthy subjects and 16 depressive patients) underwent genotyping for Val66Met and PET imaging with the 5-HTT specific radioligand [11C]DASB. Additionally, in 51 healthy subjects Val66Met genotypes and 5-HT1A binding with the radioligand [carbonyl-11C]WAY-100635 were ascertained. Voxel-wise and region of interest-based analyses of variance were used to examine the influence of Val66Met on 5-HTT and 5-HT1A BPND.ResultsNo significant differences of 5-HTT nor 5-HT1A BPND between BDNF Val66Met genotype groups (val/val vs. met-carrier) were detected. There was no interaction between depression and Val66Met genotype status.ConclusionIn line with previous data, our work confirms an absent effect of BDNF Val66Met on two major serotonergic structures. These results could suggest that altered protein expression associated with genetic variants, might be compensated in vivo by several levels of unknown feedback mechanisms. In conclusion, Val66Met genotype status is not associated with changes of in-vivo binding of 5-HTT and 5-HT1A receptors in human subjects.

Lower Level of Endogenous Dopamine in Patients With Cocaine Dependence: Findings From PET Imaging of D 2 /D 3 Receptors Following Acute Dopamine Depletion

Previous positron emission tomography (PET) imaging studies have demonstrated that cocaine dependence is associated with a decrease in dopamine type 2 and 3 (D(2)/D(3)) receptor binding in cocaine-dependent individuals relative to healthy comparison subjects. However, given the nature of PET imaging, it is possible that the measured decrease in radiotracer binding results from an increase in baseline dopamine levels. The purpose of this study was to measure D(2)/D(3) receptors following acute dopamine depletion in cocaine-dependent volunteers relative to healthy comparison subjects. Cocaine-dependent volunteers (N=15) and healthy matched comparison subjects (N=15) were scanned using PET, with the dopamine receptor radiotracer [(11)C]raclopride, at baseline and again following acute depletion of endogenous dopamine via alpha-methyl-para-tyrosine (AMPT) administration. Changes in radiotracer binding were measured in the subdivisions of the striatum (caudate, putamen, and ventral striatum) in addition to the striatum as a whole. Findings revealed that cocaine-dependent volunteers exhibited lower levels of endogenous dopamine relative to comparison subjects, which was measured as an increase in [(11)C]raclopride binding following AMPT administration. The increase in [(11)C]raclopride binding in the striatum was 11.1% (SD=4.4%) in healthy comparison subjects and 5.7% (SD=5.9%) in cocaine-dependent volunteers. Similar differences were seen in the subdivisions of the striatum. The decrease in striatal D(2)/D(3 )receptors associated with cocaine dependence cannot be attributed to higher levels of endogenous dopamine.

Salvinorin A and derivatives: Protection from metabolism does not prolong short-term, whole-brain residence

Salvinorin A (SA) is a potent kappa opioid agonist with a brief duration of action. Consistent with this, our previous positron emission tomography (PET) studies of carbon-11 labeled SA showed that brain levels decrease rapidly after intravenous administration. SA is rapidly metabolized, giving the much less potent salvinorin B (SB), which is presumed to be responsible in part for SA's brief duration of action. To test this, we labeled the metabolically stable methyl ester of SA and SB with carbon-11 and compared their pharmacokinetics by PET imaging after intravenous administration to baboons. Labeling of salvinorin B ethoxymethyl ether (EOM-SB), a derivative with greater potency and resistance to metabolism, provided an additional test of the role of metabolism in brain efflux. Plasma analysis confirmed that SB and EOM-SB exhibited greater metabolic stability than SA. However, the three compounds exhibited very similar pharmacokinetics in brain, entering and exiting rapidly. This suggests that metabolism is not solely responsible for the brief brain residence time of SA. We determined that whole-brain concentrations of EOM-SB declined more slowly than SA after intraperitoneal administration in rodents. This is likely due to a combination in EOM-SB's increased metabolic stability and its decreased plasma protein affinity. Our results suggest that protecting salvinorin A derivatives from metabolism will prolong duration of action, but only when administered by routes giving slow absorption.

Striatal Dopamine Synthesis in First-degree Relatives of Patients with Schizophrenia

First degree relatives (FDR) of patients with schizophrenia have higher risk of developing schizophrenia than the general population. Previous positron emission tomography (PET) studies have shown that striatal presynaptic dopamine synthesis capacity is increased in schizophrenia. We investigated whether this same phenomenon is shared by individuals with increased genetic risk for schizophrenia. We used 6-[18F]-fluorodopa (FDOPA) PET imaging to measure striatal dopamine synthesis capacity. We studied 17 nonpsychotic subjects with an FDR with schizophrenia. This group was compared to 17 healthy subjects with no FDRs with schizophrenia. A conventional region of interest (ROI)-analysis indicated that FDOPA uptake (K(i)) in the caudate-putamen was statistically significantly higher in the FDR group than in the control group. A voxel-level analysis confirmed these results. These results suggest that the changes of striatal presynaptic dopamine synthesis seen previously in neuroleptic-naive schizophrenic patients is also present in FDRs of patients with schizophrenia. These findings have implications for the early detection of psychosis as well as for pharmacological interventions in individuals at risk for psychosis.

Increased 5-HT 2A Receptor Binding in Euthymic, Medication-Free Patients Recovered From Depression: A Positron Emission Study With [ 11 C]MDL 100,907

A previous positron emission tomography (PET) study reported increased serotonin 5-HT(2A) receptor binding in unmedicated depressed patients with high scores on the Dysfunctional Attitudes Scale. The purpose of the present study was to use the highly selective 5-HT(2A) receptor ligand [(11)C]MDL 100,907 in a PET imaging paradigm to assess 1) 5-HT(2A) receptor binding potential in euthymic subjects with a history of recurrent depression and 2) the relationship between receptor binding and scores on the Dysfunctional Attitudes Scale. Cortical 5-HT(2A) receptor binding was measured in 20 unmedicated, fully recovered unipolar depressed patients and 20 age- and gender-matched comparison subjects. Regional estimates of binding potential were obtained using a reversible plasma input function compartmental model and the cerebellum as a reference region to estimate the free and non-specifically bound [(11)C]MDL 100,907 in brain tissue. Relative to the comparison subjects, the recovered depressed patients demonstrated significantly higher 5-HT(2A) receptor binding potential in the frontal cortex (mean increase: 19%), parietal cortex (mean increase: 25%), and occipital cortex (mean increase: 19%). 5-HT(2A) receptor binding potential correlated negatively with age in both patients and comparison subjects and positively with the Dysfunctional Attitudes Scale in the recovered patients. These findings should be considered preliminary but suggest that recovered subjects with a history of recurrent major depression have elevated binding potential of cortical 5-HT(2A) receptors. The correlation of increased 5-HT(2A) receptor binding potential with increased scores on Dysfunctional Attitudes Scale supports earlier work suggesting that increased 5-HT(2A) receptor availability characterizes a group of depressed patients with high levels of dysfunctional attitudes.

Increased 5-HT<char aid="99820963" id="sub">2A</char> Receptor Binding in Euthymic, Medication-Free Patients Recovered From Depression: A Positron Emission Study With [<char aid="99820964" id="sup">11</char>C]MDL 100,907

Objective: A previous positron emission tomography (PET) study reported increased serotonin 5-HT 2A receptor binding in unmedicated depressed patients with high scores on the Dysfunctional Attitudes Scale. The purpose of the present study was to use the highly selective 5-HT 2A receptor ligand [ 11 C]MDL 100,907 in a PET imaging paradigm to assess 1) 5-HT 2A receptor binding potential in euthymic subjects with a history of recurrent depression and 2) the relationship between receptor binding and scores on the Dysfunctional Attitudes Scale. Method: Cortical 5-HT 2A receptor binding was measured in 20 unmedicated, fully recovered unipolar depressed patients and 20 age- and gender-matched comparison subjects. Regional estimates of binding potential were obtained using a reversible plasma input function compartmental model and the cerebellum as a reference region to estimate the free and non-specifically bound [ 11 C]MDL 100,907 in brain tissue. Results: Relative to the comparison subjects, the recovered depressed patients demonstrated significantly higher 5-HT 2A receptor binding potential in the frontal cortex (mean increase: 19%), parietal cortex (mean increase: 25%), and occipital cortex (mean increase: 19%). 5-HT 2A receptor binding potential correlated negatively with age in both patients and comparison subjects and positively with the Dysfunctional Attitudes Scale in the recovered patients. Conclusions: These findings should be considered preliminary but suggest that recovered subjects with a history of recurrent major depression have elevated binding potential of cortical 5-HT 2A receptors. The correlation of increased 5-HT 2A receptor binding potential with increased scores on Dysfunctional Attitudes Scale supports earlier work suggesting that increased 5-HT 2A receptor availability characterizes a group of depressed patients with high levels of dysfunctional attitudes.

Impaired sequence learning in carriers of the DYT1 dystonia mutation.

Previous positron emission tomography (PET) studies have shown that nonmanifesting carriers of the DYT1 dystonia mutation express an abnormal pattern of resting glucose metabolism. To determine whether motor behavior is impaired in these subjects, we compared movement and sequence learning in 12 clinically unaffected DYT1 carriers with 12 age-matched controls. Regional differences in brain function during task performance were assessed with simultaneous H(2) (15)O/PET. We found that motor performance was similar in the DYT1 and control groups, with no significant differences in movement time and spatial accuracy measured during each of the tasks. In contrast, sequence learning was reduced in gene carriers relative to controls (p < 0.01). PET imaging during motor execution showed increased activation in gene carriers (p < 0.001, uncorrected) in the left premotor cortex and right supplementary motor area, with concomitant reduction in the posterior medial cerebellum. During sequence learning, activation responses in DYT1 carriers were increased in the left ventral prefrontal cortex, and lateral cerebellum. These findings suggest that abnormalities in motor behavior and brain function exist in clinically nonmanifesting DYT1 carriers. Although localized increases in neural activity may enable normal movement execution in these subjects, this mechanism may not compensate for their defect in sequence learning.